The main objective of MONARCH-A FP7 European program is to generate a dedicated information packa... more The main objective of MONARCH-A FP7 European program is to generate a dedicated information package tailored to a subset of multidisciplinary essential climate variables and their mutual forcing and feedback mechanisms associated with changes in terrestrial carbon and water fluxes, sea level and ocean circulation and the marine carbon cycle in the high latitude and Arctic regions. High latitude regions are predicted to suffer much greater warming than lower latitudes as a result of climate change. This will cause drastic changes in the carbon and water balance of the region, with associated large effects on snow cover, soil freeze-thaw periods, soil moisture, permafrost, growing season, land cover, greenhouse gas fluxes and albedo. Of crucial concern are the feedbacks between these land surface processes and climate warming; this is recognized as one of the greatest sources of uncertainty in climate prediction (IPCC 2007). Decadal change in snow properties and dynamics of high latit...
Climate change in Siberia and more generally in high latitudes, is impacting strongly the environ... more Climate change in Siberia and more generally in high latitudes, is impacting strongly the environment and the societies. If the present climate warming evolves as projected, these impacts are likely to increase, greatly affecting ecosystems, cultures, lifestyles and economies. The CLASSIQUE French research project is focused on these questions, with a special attention to land cover evolution, forest vulnerability and permafrost reduction in Siberia. It mobilizes climatologists, hydrologists, agronomists, demographers, geographers and specialists of scientific mediation in a trans-disciplinary effort to better quantify (1) future changes of climate and vegetation properties in Siberia; (2) the consecutive evolution of the agricultural potential of the region; (3) the demographic and societal effects of these changes; and (4) the interactions and feedbacks induced. The chosen approach aims to develop integrated models able to predict the evolution of land cover and hydrology and the ...
An accurate and continuous monitoring of lakes and inland seas is available since 1993 thanks to ... more An accurate and continuous monitoring of lakes and inland seas is available since 1993 thanks to the satellite altimetry missions (Topex-Poseidon, GFO, ERS-2, Jason-1, Jason-2 and Envisat). Global data processing of these satellites provides temporal and spatial time series of lakes surface height with a decimetre precision on the whole Earth. The response of water level to regional hydrology is particularly marked for lakes and inland seas in semi-arid regions. A lake data centre is under development at by LEGOS (Laboratoire d'Etude en Géophysique et Océanographie Spatiale) in Toulouse, in coordination with the HYDROLARE project (Headed by SHI: State Hydrological Institute of the Russian Academy of Science). It already provides level variations for about 150 lakes and reservoirs, freely available on the web site (HYDROWEB: http://www.LEGOS.obs-mip.fr/soa/hydrologie/HYDROWEB), and surface-volume variations of about 50 big lakes are also calculated through a combination of various satellite images (Modis, Asar, Landsat, Cbers) and radar altimetry. The final objective is to achieve in 2011 a fully operating data centre based on remote sensing technique and controlled by the in situ infrastructure for the Global Terrestrial Network for Lakes (GTN-L) under the supervision of WMO (World Meteorological Organization) and GCOS (Global Climate Observing System). (J.-F. Crétaux).
The paper aims to quantitatively estimate the role of snowmelt in the spring flood flow and the r... more The paper aims to quantitatively estimate the role of snowmelt in the spring flood flow and the redistribution of river runoff for the Northern (arctic) part of the Western Siberian plain (the rivers Poluy, Nadym, Pur and Taz). In this region, presence of wetlands and thermokarst lakes significantly influence seasonal redistribution of the river discharge. First the study region is described, and the snow regime from in situ observations at the Tarko-Sale meteorological station is analysed. As SSM/I estimates of snow depth for this region are lower than in situ observations, a correction of the SSM/I snow depth estimates is done using snow parameters measured on the snow transect near the meteorological station Tarko-Sale for 1991-1996. This re-estimated snow depth is then used to assess the volume of water stored every winter on the watersheds for 1989-2006. This snow product is compared with the spring flood streamflow estimated from in situ observations, and the regional relation between the snow water storage and flood flow is constructed. The proportion of melt water that does not reach the main rivers and is thus evaporated or stored by the wetlands is estimated to be on average 30% (varying from 10 to 64%). We observe an increasing trend of this value from 20-30% in the early 1990ies to 50-60% in the mid 2000ies. This increase could be attributed to several factors such as increase of air temperature (leading to increase of evaporation, changes in vegetation cover and active layer depth), but also to human activity.
The paper discusses time and space variations of ice extent in the Caspian and Aral seas during t... more The paper discusses time and space variations of ice extent in the Caspian and Aral seas during the last decade (1992-2002). It uses synergy of data from active (radar altimeter) and passive (radiometer) microwave nadir-looking instruments onboard the TOPEX/Poseidon satellite. The proposed approach is substantiated and validated using both in situ and satellite imagery data for the Caspian Sea. The results indicate significant spatial and temporal variability of ice conditions, with a significant decrease of both the duration of ice season and ice extent during the last four winters (1998-2002). The TOPEX/Poseidon-derived time series of sea ice extent are very valuable in view of the fragmentary and mostly unpublished data on ice conditions on the Caspian and Aral seas since the mid-1980s.
Continental waters represent a tiny part of the total water amount on Earth, but play a major rol... more Continental waters represent a tiny part of the total water amount on Earth, but play a major role in climate variability and have paramount importance for terrestrial ecosystems and human needs. They are an integral part of the global climate system with important links and feedbacks generated through its influence on surface energy and moisture fluxes between continental water, atmosphere and oceans. It is important to well understand what are temporal and spatial scales of variability of continental waters, what are teleconnections, feedbacks and mechanisms responsible for the changes, what are natural and anthropogenic causes of recent and historical changes in the hydrometeorological parameters. In this respect, continental hydrology is one of the research fields where acquired knowledge and understanding of natural processes will benefit from combination of conventional observations with data from SMOS and other Earth Observation satellites. We present studies of two key regions where SMOS data have the potential to significantly expand the potential of scientific and applied studies: a) Western Siberia and b) Euphrates-Tigris river system. Main part of the Western Siberia is covered by Ob' river system; which will be the main object of study for this region. This river basin is characterised by large flooded areas, frequently described as the biggest world swamp. Wetlands are also an important source of methane and source/sink for the CO2. Although wetlands played a key role in the natural variations of carbon cycle during the last climatic cycles, their temporal and spatial variations are still poorly modelled. As a consequence, it is very difficult to predict the effect of their variations with climate change and the resulting effect on the carbon cycle for the next decades. Water resources of the extensive Euphrates-Tigris (ET) river basin have vital importance for people living on its watershed, and for its ecosystems. This river basin also provides freshwater input into the Arabian Gulf, affecting fishery, marine biology and biogeochemistry. ET basin is shared by several countries and is extensively used for irrigation and other types for water consumption. Cascades of large reservoirs are constructed in each of the four countries. Information on hydrological regime of the ET basin (water level in the reservoirs, amount of diverted water, river level and discharge) has paramount importance for studies of natural and anthropogenic influence on ET river system, and freshwater input into the Arabian Gulf. We present the results of studies for these two regions basing on our existing experience of using in situ data together with remote sensing techniques such as radar altimetry (TOPEX/Poseidon, Jason-1, GFO, ENVISAT), radiometry (SMMR, SSM/I), optical data (MODIS, Landsat) and space gravimetry data (GRACE). We analyse several parameters: a) water level in reservoirs and wetlands, b) river level and river discharge, c) water abundance and flooded area extent, and d) snow and ice cover (for Western Siberia). Research has been done in the framework of the Russian-French cooperation GDRI CAR-WET-SIB, French ANR IMPACT-Boreal project, and SMOS AO No. 4648.
Accurate and continuous monitoring of lakes and inlands seas are available since 1991 thanks to t... more Accurate and continuous monitoring of lakes and inlands seas are available since 1991 thanks to the recent missions of satellite altimetry (Topex-Poseidon, ERS-1, ERS-2, Jason-1 and Envisat). Global processing of the data of these satellites could provide temporal and spatial times series of lakes surface height from 1991 to 2003 on the whole Earth with a decimeter precision. The response of water level to regional hydrology is particularly marked for lakes and inland seas of semi-arid regions. Altimetry data can provide invaluable source of information in hydrology sciences, but in-situ data (rivers runoff, temperature, or precipitation) are still strongly needed to study the evolution of water mass balance of each lakes. Lake level variations can however be used as interesting constrained parameter in ungauging lake basin for water mass balance budget. Recent studies based on Topex-Pose‹don data have shown evidence of significant inter-annual variations of the Caspian or the Aral sea levels. Analysis of Baikal, Issykkul, Balkhash and Hovsgol lakes level from 1993 to 2003 is also presented.
The paper discusses application of active and passive microwave data for assessment of time and s... more The paper discusses application of active and passive microwave data for assessment of time and space variations of firstyear ice cover. The Caspian and Aral Seas are chosen as main study areas. The Caspian Sea evolution is primarily climate driven, while for the Aral Sea there is a mix of anthropic and climate factors. We analyze ice cover conditions using a novel method that combines active and passive satellite measurements for ice discrimination. This method uses the synergy of simultaneous data from active (radar altimeter) and passive (radiometer) microwave instruments onboard the TOPEX/Poseidon (T/P) satellite, launched in 1992. The benefits, drawbacks, and potential of ice cover studies using the proposed method are discussed. We analyze in detail how this method is influenced by the difference in footprints of the T/P sensors and by the radiometric properties of ice and snow at different stages of ice cover evolution. In order to link the T/P-derived results to historical observations that end in the mid-1980s, long time series of passive microwave data from SMMR and SSM/I sensors have also been analyzed. Satellite time series of ice cover extent and duration of ice period have been obtained for the Caspian and Aral Seas since 1978. A good agreement is obtained between historical and satellite data, with significant spatial and temporal variability of ice conditions. There is a marked decrease of both duration of ice season and ice extent during the winters 1998/1999-2001/2002. These satellite-derived time series of sea ice parameters are very valuable in view of the heterogeneous and mostly unpublished data on ice conditions over the Caspian and Aral Sea since the mid-1980s.
The evolution of the snow cover maximum extent and of the timing of the spring snow melt has been... more The evolution of the snow cover maximum extent and of the timing of the spring snow melt has been analysed in the boreal regions with the 20 year satellite passive microwave data set. This work is part of the AICSEX project from the 5th Framework Programme of the European Community. The data set starts in 1979 with the SMMR (Scanning Multichannel Microwave Radiometer) instrument onboard the satellite NIMBUS-7 and continues since 1987 with the SSMI (Special Sensor Microwave Imager) instrument on board the DMSP (Defence Meteorological Satellite Program) series. The spatio-temporal evolution of the satellite-derived yearly snow maximum extent and the timing of the spring snow melt have been obtained and analysed over the boreal regions. Significant differences between the evolution of the yearly maximum snow extent in Eurasia and in North America are found. The maximum snow extent in the boreal regions has been decreasing from about 45 millions km2 to approximately 40 millions km2 since 1980, a global decrease of 11 percent, which reaches 13 percent in Eurasia and 8 percent in North America. A positive correlation between the maximum yearly snow cover extent and the ENSO index is found. High interannual spatio-temporal variability characterises the timing of snow melt in the spring. Twenty year trends in the timing of spring snow melt have been computed and compared to spring air temperature trends, for the same period and the same area, using the NCEP (National Center for Environmental Prediction) air temperature reanalysis. In most parts of Eurasia and the central and western parts of North America there is a tendency for snow to melt earlier. In north-eastern Canada, a large area of positive trends, where snow melt timing starts later than in the early 1980s, corresponds to a region of positive trends of spring air temperature observed over the same time period.
International Lakes which aim to strengthen national measures for the protection and ecologically... more International Lakes which aim to strengthen national measures for the protection and ecologically sound management of trans-boundary surface waters and groundwater and establish concrete procedural obligations of cooperation between littoral states. They also include provisions for monitoring, research and development, consultations, warning and alarm systems, mutual assistance, institutional arrangements, and exchange and protection of information, as well as public access to information.
The Western Siberian Plain is the most bogged region of the world - in some parts up to 70-80% of... more The Western Siberian Plain is the most bogged region of the world - in some parts up to 70-80% of its territory is covered by bogs. For the last 10 thousand years wetland areas of Western Siberia have been extending their territories, acting as a terrestrial sink of atmospheric carbon on our planet. Two contrasting processes are actually occurring in the Southern and Northern parts of the region. In the south, there is a progressive swamping which leads to forest death. In the north, there is a thermokarst activity or thawing permafrost in palsas of sub-arctic zone of Western Siberia. In this work we analyse the hydrological and ecological indicators which characterize natural conditions of the North-Western Siberian Wetlands (watershed of Pur, Taz and Nadym rivers). These three rivers have total watershed of 243 000 km2 and discharge of 76 km3/year. They originate on the northern slopes of Sibirskiye uvaly ridge and flow to the Ob' bay and then to the Kara sea in the Arctic. Flat relief and the presence of permafrost lead to development of various forms of water objects and wetlands, such as river systems, flooded zones, lakes and bogs. We present the results of systematization and classification of landscape patterns, as well as study of variability of hydrological processes in the study region at different temporal (from multi-year to seasonal) and spatial (from local to regional) scales through a multidisciplinary approach based on in situ and remote sensing data. Various sources of satellite Earth observations, such as radar altimetry (TOPEX/Poseidon, ENVISAT), radiometry (SMMR, SSM/I), optical data (Landsat) and space gravimetry data (GRACE) are used in combination with the in situ observations and the recent field studies done in the August 2008. This research has been done in the framework of the Russian-French cooperation GDRI "CAR-WET-SIB" and French ANR "IMPACT-Boreal" project.
Stable ice cover forms every year in the Caspian and Aral seas. Ice stays for several months and ... more Stable ice cover forms every year in the Caspian and Aral seas. Ice stays for several months and negatively affects navigation conditions, endangers constructions located on the coast and the oil rigs that have recently been installed in the shelf regions of the Northern Caspian by Russia and Kazakhstan. Ice extent varies significantly from year to year in response to changes in hydrometeorological conditions over the region and its variations may serve as an early indicator of the large-scale climate change. We studied ice cover in these two seas using data from the Topex-Poseidon satellite, operating since 1992. This platform has two nadir-looking instruments - a dual-frequency radar altimeter and a passive microwave radiometer. Five Topex-Poseidon passes covering the northern part of the Caspian sea and two passes covering the central part of the Big Aral sea, were selected, providing data for ten consecutive years with a 10 days repetitive period. The combination of both active (backscatter coefficient at 13 GHz) and passive (brightness temperature at 18 and 37 GHz) microwave measurements provides information to estimate ice concentration, roughness and height of snow cover on ice. This information on ice cover was complemented by passive microwave data from the SMMR (Scanning Multichannel Microwave Radiometer) instrument onboard the satellite NIMBUS-7 (since 1979) and the SSMI (Special Sensor Microwave Imager) instrument on board the DMSP (Defense Meteorological Satellite Program) series (since 1987). Analysis of time series of ice extent and types shows pronounced regional, seasonal and interannual variability. In the Northern Caspian sea ice cover has a maximum extent in the shallow and isolated eastern part, while in the western part presence of ice cover is reduced. Interannual variability of ice cover extent for ten selected years show a warming signal: ratio of presence of ice cover in observations in both Caspian and Aral seas is reduced (more than two times), especially during the four unusually mild winters (1998/99 to 2001/02). In the Caspian sea such dramatic reduction of ice extent affects breeding habits and living conditions of the Caspian seal - the only mammal in this sea.
We show how the studies of ice and snow cover of continental water bodies can benefit from the sy... more We show how the studies of ice and snow cover of continental water bodies can benefit from the synergy of more than 15 years-long simultaneous active (radar altimeter) and passive (radiometer) observations from radar altimetric satellites (TOPEX/Poseidon, Jason-1, ENVISAT and Geosat Follow-On) and how this approach can be complemented by SSM/I passive microwave data to improve spatial and temporal coverage. Five largest Eurasian continental water bodies - Caspian and Aral seas, Baikal, Ladoga and Onega lakes are selected as examples. A step-by-step ice discrimination approach based on a combined use of the data from the four altimetric missions and SSM/I is presented, as well as validation of this approach using in situ and independent satellite data in the visible range. We also discuss drawbacks and benefits of each type of sensor and particularities of radiometric properties for each of the chosen water bodies. We then analyse the long-term evolution of ice conditions for these lakes and inland seas using historical data and recent observations from satellite radar altimetry and radiometry.
Drained thaw lake basins in Western Siberia have a local name "khasyreis" [1]. Khasyreis as well ... more Drained thaw lake basins in Western Siberia have a local name "khasyreis" [1]. Khasyreis as well as lakes, ponds and frozen mounds are invariable element of sub-arctic frozen peat bogs - palsas and tundra landscapes. In some areas of West-Siberian sub-arctic khasyreis occupy up to 40-50% of total lake area. Sometimes their concentration is so high that we call such places ‘khasyrei's fields". Khasyreis are part of the natural cycle of palsa complex development [1], but their origin is not continuous and uniform in time and, according to our opinion, there were periods of more intensive lake drainage and khasyrei development accordingly. These times were corresponding with epochs of climatic warming and today we have faced with one of them. So, last years this process was sufficiently activated in the south part of West-Siberian sub-arctic [2]. It was discovered that in the zone of continuous permafrost thermokarst lakes have expanded their areas by about 10-12%, but in the zone of discontinuous permafrost the process of their drainage prevails. These features are connected with the thickness of peat layers which gradually decreases to the North, and thus have reduced the opportunity for lake drainage in northern areas. The most typical way of khasyrei origin is their drainage to the bigger lakes which are always situated on the lower levels and works as a collecting funnels providing drainage of smaller lakes. The lower level of the big lake appeared when the lake takes a critical mass of water enough for subsidence of the lake bottom due to the melting of underlaying rocks [2]. Another one way of lake drainage is the lake intercept by any river. Lake drainage to the subsurface (underlaying rocks) as some authors think [3, 4] is not possible in Western Siberia, because the thickness of permafrost is at list 500 m here being safe confining bed. We mark out few stages of khasyrei development: freshly drained, young, mature and old. This row reflects stages of repeated permafrost heaving from small declustered frozen mounds to recovery of palsa plateaus due to growing and merging of isolated mounds. It was shown that satellite altimetry, which was applied for the first time in permafrost zone in the framework of Russian-French project CAR-WET-SIB, is a prospective method to study lakes and khasyreis state and dynamic. References [1] Kirpotin S.N., Naumov A .V., Vorobiov S.N., Mironycheva-Tokareva N.P., Kosych N.P., Lapshina E.D., Marquand J., Kulizhski S.P., Bleuten W. 2007. Western-Siberian Peatlands: Indicators of Climate Change and Their Role in Global Carbon Balance. Chapter 33 in Climate Change and Terrestrial Carbon Sequestration in Central Asia / edited by R.Lal, M.Suleimenov, B.A.Stewart, D.O.Hansen, and P.Doraiswamy, Taylor and Francis, Amsterdam, Holland, pp. 453-472. [2] Kirpotin S., Polishchuk Yu., Zakharova E., Shirokova L., Pokrovsky O., Kolmakova M., Dupre B. 2008. One of Possible Mechanisms of Thermokarst Lakes Drainage in West-Siberian North // International Journal of Environmental Studies. Vol.65, No 5, October 2008, 631-635. [3] Smith, L.C., Sheng, Y., McDonald, G.M., Hinzman, L.D. 2005. Disappearing Arctic Lakes, Science, 308, 1429 [4] Hinkel, K.M., Eisner, W.R., Bockheim, J.G., Nelson, F.E., Peterson, K.M., and Dai, X. 2003. Spatial Extent, Age, and Carbon Stoks in Drained Thaw Lake Basins on the Barrow Peninsula. Alaska. Arctic, Antarctic, and Alpine Research, 35, 3, 291-300.
Western Siberia is a large region with mostly flat relief. Most of its territory comprises the wa... more Western Siberia is a large region with mostly flat relief. Most of its territory comprises the watershed of the Ob' river, and much smaller part in the north - watersheds of Nadym, Pur and Taz rivers. Flat relief significantly affects the hydrographical network, creating a multitude of interconnected natural objects - large and small rivers streams, large floodplains, lakes, bogs etc. The region is also abundant with lakes, mainly small ones with surface area less than 1 km2 and depths of 2-5 m. Flooded areas and bogs also act as a buffer zone, providing a dampening "sponge" effect on the water redistribution within the river system. Large area covered by rivers and wetlands results in high rate of evaporation compared to any other large boreal watershed. Contrasting processes are occurring in the Southern and Northern parts of the Western Siberian Plain. In the south, bogs are expanding in the taiga zone and there is progressive swamping which leads to forest death. These bogs act as a carbon sink due to carbon sequestration in their peat layers. Among the bogs of this part of Western Siberia there is the Great Vasiugan Bog - world's largest peatland with a total area of 6.78 million hectares. Bogs of Vasyugan have appeared about 10 000 years ago and since then are constantly growing. 75% of the actual surface of the Great Vasyugan Bog have appeared during the last 500 years. The situation in the northern part (affected by permafrost) is different. The bogs there are reducing their surface and the forest-tundra regions are being subjected to thermokarst activity and colonisation of bogs by trees. Two contrast processes are observed here - a) increase of lake surface due to melting of lakes' coasts, and b) decrease of surface area or disappearance of lakes due to water drain downstream the hydrological network. We combine in situ observations with satellite remote sensing to monitor hydrological regime of the Western Siberian wetlands. Radar altimetry (TOPEX/Poseidon, Jason-1, GFO, ENVISAT), radiometry (SMMR, SSM/I), optical data (Landsat) and space gravimetry data (GRACE) are used in combination with the in situ observations and the recent field studies done in the August 2008. We present the variability of water level (from radar altimetry) and surface properties (from altimeter waveforms parameters) for the region of Nadym, Pur and Taz rivers, as well as for Vasyugan bog. Seasonal and interannual variability of water abundance is studied using radar altimetry, radiometry, and gravimetry. We also use active and passive microwave observations (radar altimeters and radiometers) to analyse internannual variability ice formation and break-up dates along the Ob' river, which is frozen for more than 7 month in the north and for 5-7 month in the south. This research has been done in the framework of the Russian-French cooperation GDRI "CAR-WET-SIB" and French ANR "IMPACT-Boreal" project.
Accurate and continuous monitoring of lakes and inland seas is possible since 1991 thanks to the ... more Accurate and continuous monitoring of lakes and inland seas is possible since 1991 thanks to the recent missions of satellite altimetry (Topex-Poseidon, ERS-1, ERS-2, Jason-1 and Envisat). Global processing of the data of these satellites could provide temporal and spatial times series of lakes water level from 1991 to 2003 on the whole Earth with a decimeter precision. The response of water level to regional hydrology is particularly marked for lakes and inland seas of semi-arid regions. Altimetry data can provide an invaluable source of information in hydrology sciences, but insitu data (rivers runoff, temperature, precipitation etc.) are still strongly needed to study the evolution of water mass balance of each lake. Moreover, sea level variations that result from variation of hydrological parameters such as river discharge, precipitation and evaporation, are very sensitive indicators of regional climate variations. Recent results obtained on Aral Sea and Issykkul Lake are presented here. Inter — annual changes of water level have been obtained over these lakes that must be interpreted in term of hydrological water balance. Since 1960 the Aral sea has been drying and since 1989 it is divided into two lakes that follow different evolution, the Big Aral in the south which continuously dried up the last 10 years, while the so- called Small Aral in the north presented large inter-annual fluctuations related to constructions and destructions of a dam in the Berg’s strait retaining the water from the Syr Darya. For Issykkul, a slow decrease of the level has been observed over the last hundreds years (4 cm / year), followed by an abrupt and bigger increase of the level of around 10 cm/yr since 1998. The impact on local populations and infra-structures of these fluctuations are dramatic in the case of Aral, much less in the case of Issykkul, but comparative study of both water bodies may help in the future to understand the respective consequences of human-induced activities from the natural changes. It is also the task of a new project recently submitted and accepted by the NATO with scientists from Uzbekistan and Kyrgyz Republic.
We show how the studies of ice and snow cover of continental water bodies can benefit from the sy... more We show how the studies of ice and snow cover of continental water bodies can benefit from the synergy of more than 15 years-long simultaneous active (radar altimeter) and passive (radiometer) observations from radar altimetric satellites (TOPEX/Poseidon, Jason-1, ENVISAT and Geosat Follow-On) and how this approach can be complemented by SSM/I passive microwave data to improve spatial and temporal coverage. Five largest Eurasian continental water bodies—Caspian and Aral seas, Baikal, Ladoga and Onega lakes are selected as examples. First we provide an overview of ice regime and history of ice studies for these seas and lakes. Then a summary of the existing state of the art of ice discrimination methodology from altimetric observations and SSM/I is given. The drawbacks and benefits of each type of sensor and particularities of radiometric properties for each of the chosen water bodies are discussed. Influence of sensor footprint size, ice roughness and snow cover on satellite measurements is also addressed. A step-by-step ice discrimination approach based on a combined use of the data from the four altimetric missions and SSM/I is presented, as well as validation of this approach using in situ and independent satellite data in the visible range. The potential for measurement of snow depth on ice from passive microwave observations using both altimeters and SSM/I is addressed and a qualitative comparison of in situ snow depth observations and satellite-derived estimates is made.
We address spatial and temporal variability of ice conditions in the Aral Sea from historical obs... more We address spatial and temporal variability of ice conditions in the Aral Sea from historical observations and recent satellite microwave observations. A short description of the historical evolution of the Aral Sea since the mid-twentieth century is given, as well as recent activities related to the dam in the Berg strait. An overview of historical observations of the ice regime at the coastal stations and using aerial surveys is provided. The lack of reliable in situ measurements and time series for ice cover parameters since the mid-1980s may be successfully overcome by using active and passive microwave satellite observations, which provide reliable, regular, frequent, and weather-independent data. An ice discrimination methodology, based on the synergy of active and passive data from radar altimeters TOPEX/Poseidon, Jason-1, ENVISAT and Geosat Follow-On (GFO) satellites, as well as the SMMR and SSM/I radiometers is presented. This methodology has been applied to the entire satellite dataset to define specific dates of ice events (first appearance of ice, formation of stable ice cover, appearance of open water and the complete disappearance of ice) for both the Small Aral and Eastern Large Aral. The resulting time series of ice cover parameters are analysed in the context of available in situ observations. First we complement historical observations by satellite imagery in the visible range to illustrate spatial patterns in ice formation, development and decay prior to the late 1980s and in recent time. Then we address interannual variability of timing of ice events and severity of ice conditions since the earliest coastal observations (1940s) until now (2006/2007). Finally, we discuss temporal variability of ice regime parameters in the context of air temperature, bottom morphology and salinity changes.
The Aral Sea has drastically shrunk over the past 50 years, largely due to water withdrawal from ... more The Aral Sea has drastically shrunk over the past 50 years, largely due to water withdrawal from the Amudarya and Syrdarya rivers for land irrigation. If one were to look back over the Holocene,1 the paleolimnology of the Aral Sea is however already marked by the occurrence of several phases of regression and transgression. They resulted partly from climate change, for tectonic reasons, and over the last 2,000 years anthropogenic actions also played a role. After a short review of the paleohistory of the Aral Sea, we will focus on a description of the causes and magnitude of episodes of historical (last 100 years) Aral Sea level variability. The Aral Sea has been marked since the middle of the last century by a process of desiccation due to increase of water intake from the Amudarya and Syrdarya rivers for agricultural purposes. This led to the separation of the Aral Sea into two (in 1986–1987) and then four (in 2009) water bodies. Measurements of Aral Sea water level and surface and water balance were carried out by both in situ gauges and remote-sensing satellite data. This allows for a better understanding of the seasonal, interannual, and decadal trend in Aral Sea water storage variations.
Lake ice grows steadily between the end of freeze-up period and the onset of break-up period as a... more Lake ice grows steadily between the end of freeze-up period and the onset of break-up period as a result of the thermodynamics of freezing water as well as dynamic ice motion on the surface. In thermodynamic thickening, the conductive heat flow controls the ice growth rate and the ice thickness, and the ice thickens downward as a result of heat loss at the top of the ice cover. There has been some demonstration of the potential of brightness temperature from passive microwave airborne radiometers to estimate ice thickness. The value of passive microwave and radar altimeter data from current satellite missions merits to be examined in this respect. The major objective of this study was estimate ice thickness from brightness temperature (TB) at 10.65 and 18.70 GHz from AMSR-E channels and the 19.35 GHz frequency channel from SSM/I on large lakes of the Northern Hemisphere (e.g. Great Bear Lake, Great Slave Lake, Lake Baikal). The evolution of horizontally and vertically polarized TB derived from AMSR-E level 2A raw brightness temperature and EASE Grid Level-3 SSM/I products was compared with ice thicknesses obtained with a previously validated thermodynamic lake ice model and in situ observations over the course of seven winter seasons (2002 and 2009), as well as with recent estimates from the Jason-2 Ku-band radar altimeter data (since 2008). Results show that both passive microwave and radar altimeter data acquired in the 10-19 GHz frequency range offer a promising means for estimating ice thickness from large northern lakes.
The main objective of MONARCH-A FP7 European program is to generate a dedicated information packa... more The main objective of MONARCH-A FP7 European program is to generate a dedicated information package tailored to a subset of multidisciplinary essential climate variables and their mutual forcing and feedback mechanisms associated with changes in terrestrial carbon and water fluxes, sea level and ocean circulation and the marine carbon cycle in the high latitude and Arctic regions. High latitude regions are predicted to suffer much greater warming than lower latitudes as a result of climate change. This will cause drastic changes in the carbon and water balance of the region, with associated large effects on snow cover, soil freeze-thaw periods, soil moisture, permafrost, growing season, land cover, greenhouse gas fluxes and albedo. Of crucial concern are the feedbacks between these land surface processes and climate warming; this is recognized as one of the greatest sources of uncertainty in climate prediction (IPCC 2007). Decadal change in snow properties and dynamics of high latit...
Climate change in Siberia and more generally in high latitudes, is impacting strongly the environ... more Climate change in Siberia and more generally in high latitudes, is impacting strongly the environment and the societies. If the present climate warming evolves as projected, these impacts are likely to increase, greatly affecting ecosystems, cultures, lifestyles and economies. The CLASSIQUE French research project is focused on these questions, with a special attention to land cover evolution, forest vulnerability and permafrost reduction in Siberia. It mobilizes climatologists, hydrologists, agronomists, demographers, geographers and specialists of scientific mediation in a trans-disciplinary effort to better quantify (1) future changes of climate and vegetation properties in Siberia; (2) the consecutive evolution of the agricultural potential of the region; (3) the demographic and societal effects of these changes; and (4) the interactions and feedbacks induced. The chosen approach aims to develop integrated models able to predict the evolution of land cover and hydrology and the ...
An accurate and continuous monitoring of lakes and inland seas is available since 1993 thanks to ... more An accurate and continuous monitoring of lakes and inland seas is available since 1993 thanks to the satellite altimetry missions (Topex-Poseidon, GFO, ERS-2, Jason-1, Jason-2 and Envisat). Global data processing of these satellites provides temporal and spatial time series of lakes surface height with a decimetre precision on the whole Earth. The response of water level to regional hydrology is particularly marked for lakes and inland seas in semi-arid regions. A lake data centre is under development at by LEGOS (Laboratoire d'Etude en Géophysique et Océanographie Spatiale) in Toulouse, in coordination with the HYDROLARE project (Headed by SHI: State Hydrological Institute of the Russian Academy of Science). It already provides level variations for about 150 lakes and reservoirs, freely available on the web site (HYDROWEB: http://www.LEGOS.obs-mip.fr/soa/hydrologie/HYDROWEB), and surface-volume variations of about 50 big lakes are also calculated through a combination of various satellite images (Modis, Asar, Landsat, Cbers) and radar altimetry. The final objective is to achieve in 2011 a fully operating data centre based on remote sensing technique and controlled by the in situ infrastructure for the Global Terrestrial Network for Lakes (GTN-L) under the supervision of WMO (World Meteorological Organization) and GCOS (Global Climate Observing System). (J.-F. Crétaux).
The paper aims to quantitatively estimate the role of snowmelt in the spring flood flow and the r... more The paper aims to quantitatively estimate the role of snowmelt in the spring flood flow and the redistribution of river runoff for the Northern (arctic) part of the Western Siberian plain (the rivers Poluy, Nadym, Pur and Taz). In this region, presence of wetlands and thermokarst lakes significantly influence seasonal redistribution of the river discharge. First the study region is described, and the snow regime from in situ observations at the Tarko-Sale meteorological station is analysed. As SSM/I estimates of snow depth for this region are lower than in situ observations, a correction of the SSM/I snow depth estimates is done using snow parameters measured on the snow transect near the meteorological station Tarko-Sale for 1991-1996. This re-estimated snow depth is then used to assess the volume of water stored every winter on the watersheds for 1989-2006. This snow product is compared with the spring flood streamflow estimated from in situ observations, and the regional relation between the snow water storage and flood flow is constructed. The proportion of melt water that does not reach the main rivers and is thus evaporated or stored by the wetlands is estimated to be on average 30% (varying from 10 to 64%). We observe an increasing trend of this value from 20-30% in the early 1990ies to 50-60% in the mid 2000ies. This increase could be attributed to several factors such as increase of air temperature (leading to increase of evaporation, changes in vegetation cover and active layer depth), but also to human activity.
The paper discusses time and space variations of ice extent in the Caspian and Aral seas during t... more The paper discusses time and space variations of ice extent in the Caspian and Aral seas during the last decade (1992-2002). It uses synergy of data from active (radar altimeter) and passive (radiometer) microwave nadir-looking instruments onboard the TOPEX/Poseidon satellite. The proposed approach is substantiated and validated using both in situ and satellite imagery data for the Caspian Sea. The results indicate significant spatial and temporal variability of ice conditions, with a significant decrease of both the duration of ice season and ice extent during the last four winters (1998-2002). The TOPEX/Poseidon-derived time series of sea ice extent are very valuable in view of the fragmentary and mostly unpublished data on ice conditions on the Caspian and Aral seas since the mid-1980s.
Continental waters represent a tiny part of the total water amount on Earth, but play a major rol... more Continental waters represent a tiny part of the total water amount on Earth, but play a major role in climate variability and have paramount importance for terrestrial ecosystems and human needs. They are an integral part of the global climate system with important links and feedbacks generated through its influence on surface energy and moisture fluxes between continental water, atmosphere and oceans. It is important to well understand what are temporal and spatial scales of variability of continental waters, what are teleconnections, feedbacks and mechanisms responsible for the changes, what are natural and anthropogenic causes of recent and historical changes in the hydrometeorological parameters. In this respect, continental hydrology is one of the research fields where acquired knowledge and understanding of natural processes will benefit from combination of conventional observations with data from SMOS and other Earth Observation satellites. We present studies of two key regions where SMOS data have the potential to significantly expand the potential of scientific and applied studies: a) Western Siberia and b) Euphrates-Tigris river system. Main part of the Western Siberia is covered by Ob' river system; which will be the main object of study for this region. This river basin is characterised by large flooded areas, frequently described as the biggest world swamp. Wetlands are also an important source of methane and source/sink for the CO2. Although wetlands played a key role in the natural variations of carbon cycle during the last climatic cycles, their temporal and spatial variations are still poorly modelled. As a consequence, it is very difficult to predict the effect of their variations with climate change and the resulting effect on the carbon cycle for the next decades. Water resources of the extensive Euphrates-Tigris (ET) river basin have vital importance for people living on its watershed, and for its ecosystems. This river basin also provides freshwater input into the Arabian Gulf, affecting fishery, marine biology and biogeochemistry. ET basin is shared by several countries and is extensively used for irrigation and other types for water consumption. Cascades of large reservoirs are constructed in each of the four countries. Information on hydrological regime of the ET basin (water level in the reservoirs, amount of diverted water, river level and discharge) has paramount importance for studies of natural and anthropogenic influence on ET river system, and freshwater input into the Arabian Gulf. We present the results of studies for these two regions basing on our existing experience of using in situ data together with remote sensing techniques such as radar altimetry (TOPEX/Poseidon, Jason-1, GFO, ENVISAT), radiometry (SMMR, SSM/I), optical data (MODIS, Landsat) and space gravimetry data (GRACE). We analyse several parameters: a) water level in reservoirs and wetlands, b) river level and river discharge, c) water abundance and flooded area extent, and d) snow and ice cover (for Western Siberia). Research has been done in the framework of the Russian-French cooperation GDRI CAR-WET-SIB, French ANR IMPACT-Boreal project, and SMOS AO No. 4648.
Accurate and continuous monitoring of lakes and inlands seas are available since 1991 thanks to t... more Accurate and continuous monitoring of lakes and inlands seas are available since 1991 thanks to the recent missions of satellite altimetry (Topex-Poseidon, ERS-1, ERS-2, Jason-1 and Envisat). Global processing of the data of these satellites could provide temporal and spatial times series of lakes surface height from 1991 to 2003 on the whole Earth with a decimeter precision. The response of water level to regional hydrology is particularly marked for lakes and inland seas of semi-arid regions. Altimetry data can provide invaluable source of information in hydrology sciences, but in-situ data (rivers runoff, temperature, or precipitation) are still strongly needed to study the evolution of water mass balance of each lakes. Lake level variations can however be used as interesting constrained parameter in ungauging lake basin for water mass balance budget. Recent studies based on Topex-Pose‹don data have shown evidence of significant inter-annual variations of the Caspian or the Aral sea levels. Analysis of Baikal, Issykkul, Balkhash and Hovsgol lakes level from 1993 to 2003 is also presented.
The paper discusses application of active and passive microwave data for assessment of time and s... more The paper discusses application of active and passive microwave data for assessment of time and space variations of firstyear ice cover. The Caspian and Aral Seas are chosen as main study areas. The Caspian Sea evolution is primarily climate driven, while for the Aral Sea there is a mix of anthropic and climate factors. We analyze ice cover conditions using a novel method that combines active and passive satellite measurements for ice discrimination. This method uses the synergy of simultaneous data from active (radar altimeter) and passive (radiometer) microwave instruments onboard the TOPEX/Poseidon (T/P) satellite, launched in 1992. The benefits, drawbacks, and potential of ice cover studies using the proposed method are discussed. We analyze in detail how this method is influenced by the difference in footprints of the T/P sensors and by the radiometric properties of ice and snow at different stages of ice cover evolution. In order to link the T/P-derived results to historical observations that end in the mid-1980s, long time series of passive microwave data from SMMR and SSM/I sensors have also been analyzed. Satellite time series of ice cover extent and duration of ice period have been obtained for the Caspian and Aral Seas since 1978. A good agreement is obtained between historical and satellite data, with significant spatial and temporal variability of ice conditions. There is a marked decrease of both duration of ice season and ice extent during the winters 1998/1999-2001/2002. These satellite-derived time series of sea ice parameters are very valuable in view of the heterogeneous and mostly unpublished data on ice conditions over the Caspian and Aral Sea since the mid-1980s.
The evolution of the snow cover maximum extent and of the timing of the spring snow melt has been... more The evolution of the snow cover maximum extent and of the timing of the spring snow melt has been analysed in the boreal regions with the 20 year satellite passive microwave data set. This work is part of the AICSEX project from the 5th Framework Programme of the European Community. The data set starts in 1979 with the SMMR (Scanning Multichannel Microwave Radiometer) instrument onboard the satellite NIMBUS-7 and continues since 1987 with the SSMI (Special Sensor Microwave Imager) instrument on board the DMSP (Defence Meteorological Satellite Program) series. The spatio-temporal evolution of the satellite-derived yearly snow maximum extent and the timing of the spring snow melt have been obtained and analysed over the boreal regions. Significant differences between the evolution of the yearly maximum snow extent in Eurasia and in North America are found. The maximum snow extent in the boreal regions has been decreasing from about 45 millions km2 to approximately 40 millions km2 since 1980, a global decrease of 11 percent, which reaches 13 percent in Eurasia and 8 percent in North America. A positive correlation between the maximum yearly snow cover extent and the ENSO index is found. High interannual spatio-temporal variability characterises the timing of snow melt in the spring. Twenty year trends in the timing of spring snow melt have been computed and compared to spring air temperature trends, for the same period and the same area, using the NCEP (National Center for Environmental Prediction) air temperature reanalysis. In most parts of Eurasia and the central and western parts of North America there is a tendency for snow to melt earlier. In north-eastern Canada, a large area of positive trends, where snow melt timing starts later than in the early 1980s, corresponds to a region of positive trends of spring air temperature observed over the same time period.
International Lakes which aim to strengthen national measures for the protection and ecologically... more International Lakes which aim to strengthen national measures for the protection and ecologically sound management of trans-boundary surface waters and groundwater and establish concrete procedural obligations of cooperation between littoral states. They also include provisions for monitoring, research and development, consultations, warning and alarm systems, mutual assistance, institutional arrangements, and exchange and protection of information, as well as public access to information.
The Western Siberian Plain is the most bogged region of the world - in some parts up to 70-80% of... more The Western Siberian Plain is the most bogged region of the world - in some parts up to 70-80% of its territory is covered by bogs. For the last 10 thousand years wetland areas of Western Siberia have been extending their territories, acting as a terrestrial sink of atmospheric carbon on our planet. Two contrasting processes are actually occurring in the Southern and Northern parts of the region. In the south, there is a progressive swamping which leads to forest death. In the north, there is a thermokarst activity or thawing permafrost in palsas of sub-arctic zone of Western Siberia. In this work we analyse the hydrological and ecological indicators which characterize natural conditions of the North-Western Siberian Wetlands (watershed of Pur, Taz and Nadym rivers). These three rivers have total watershed of 243 000 km2 and discharge of 76 km3/year. They originate on the northern slopes of Sibirskiye uvaly ridge and flow to the Ob' bay and then to the Kara sea in the Arctic. Flat relief and the presence of permafrost lead to development of various forms of water objects and wetlands, such as river systems, flooded zones, lakes and bogs. We present the results of systematization and classification of landscape patterns, as well as study of variability of hydrological processes in the study region at different temporal (from multi-year to seasonal) and spatial (from local to regional) scales through a multidisciplinary approach based on in situ and remote sensing data. Various sources of satellite Earth observations, such as radar altimetry (TOPEX/Poseidon, ENVISAT), radiometry (SMMR, SSM/I), optical data (Landsat) and space gravimetry data (GRACE) are used in combination with the in situ observations and the recent field studies done in the August 2008. This research has been done in the framework of the Russian-French cooperation GDRI "CAR-WET-SIB" and French ANR "IMPACT-Boreal" project.
Stable ice cover forms every year in the Caspian and Aral seas. Ice stays for several months and ... more Stable ice cover forms every year in the Caspian and Aral seas. Ice stays for several months and negatively affects navigation conditions, endangers constructions located on the coast and the oil rigs that have recently been installed in the shelf regions of the Northern Caspian by Russia and Kazakhstan. Ice extent varies significantly from year to year in response to changes in hydrometeorological conditions over the region and its variations may serve as an early indicator of the large-scale climate change. We studied ice cover in these two seas using data from the Topex-Poseidon satellite, operating since 1992. This platform has two nadir-looking instruments - a dual-frequency radar altimeter and a passive microwave radiometer. Five Topex-Poseidon passes covering the northern part of the Caspian sea and two passes covering the central part of the Big Aral sea, were selected, providing data for ten consecutive years with a 10 days repetitive period. The combination of both active (backscatter coefficient at 13 GHz) and passive (brightness temperature at 18 and 37 GHz) microwave measurements provides information to estimate ice concentration, roughness and height of snow cover on ice. This information on ice cover was complemented by passive microwave data from the SMMR (Scanning Multichannel Microwave Radiometer) instrument onboard the satellite NIMBUS-7 (since 1979) and the SSMI (Special Sensor Microwave Imager) instrument on board the DMSP (Defense Meteorological Satellite Program) series (since 1987). Analysis of time series of ice extent and types shows pronounced regional, seasonal and interannual variability. In the Northern Caspian sea ice cover has a maximum extent in the shallow and isolated eastern part, while in the western part presence of ice cover is reduced. Interannual variability of ice cover extent for ten selected years show a warming signal: ratio of presence of ice cover in observations in both Caspian and Aral seas is reduced (more than two times), especially during the four unusually mild winters (1998/99 to 2001/02). In the Caspian sea such dramatic reduction of ice extent affects breeding habits and living conditions of the Caspian seal - the only mammal in this sea.
We show how the studies of ice and snow cover of continental water bodies can benefit from the sy... more We show how the studies of ice and snow cover of continental water bodies can benefit from the synergy of more than 15 years-long simultaneous active (radar altimeter) and passive (radiometer) observations from radar altimetric satellites (TOPEX/Poseidon, Jason-1, ENVISAT and Geosat Follow-On) and how this approach can be complemented by SSM/I passive microwave data to improve spatial and temporal coverage. Five largest Eurasian continental water bodies - Caspian and Aral seas, Baikal, Ladoga and Onega lakes are selected as examples. A step-by-step ice discrimination approach based on a combined use of the data from the four altimetric missions and SSM/I is presented, as well as validation of this approach using in situ and independent satellite data in the visible range. We also discuss drawbacks and benefits of each type of sensor and particularities of radiometric properties for each of the chosen water bodies. We then analyse the long-term evolution of ice conditions for these lakes and inland seas using historical data and recent observations from satellite radar altimetry and radiometry.
Drained thaw lake basins in Western Siberia have a local name "khasyreis" [1]. Khasyreis as well ... more Drained thaw lake basins in Western Siberia have a local name "khasyreis" [1]. Khasyreis as well as lakes, ponds and frozen mounds are invariable element of sub-arctic frozen peat bogs - palsas and tundra landscapes. In some areas of West-Siberian sub-arctic khasyreis occupy up to 40-50% of total lake area. Sometimes their concentration is so high that we call such places ‘khasyrei's fields". Khasyreis are part of the natural cycle of palsa complex development [1], but their origin is not continuous and uniform in time and, according to our opinion, there were periods of more intensive lake drainage and khasyrei development accordingly. These times were corresponding with epochs of climatic warming and today we have faced with one of them. So, last years this process was sufficiently activated in the south part of West-Siberian sub-arctic [2]. It was discovered that in the zone of continuous permafrost thermokarst lakes have expanded their areas by about 10-12%, but in the zone of discontinuous permafrost the process of their drainage prevails. These features are connected with the thickness of peat layers which gradually decreases to the North, and thus have reduced the opportunity for lake drainage in northern areas. The most typical way of khasyrei origin is their drainage to the bigger lakes which are always situated on the lower levels and works as a collecting funnels providing drainage of smaller lakes. The lower level of the big lake appeared when the lake takes a critical mass of water enough for subsidence of the lake bottom due to the melting of underlaying rocks [2]. Another one way of lake drainage is the lake intercept by any river. Lake drainage to the subsurface (underlaying rocks) as some authors think [3, 4] is not possible in Western Siberia, because the thickness of permafrost is at list 500 m here being safe confining bed. We mark out few stages of khasyrei development: freshly drained, young, mature and old. This row reflects stages of repeated permafrost heaving from small declustered frozen mounds to recovery of palsa plateaus due to growing and merging of isolated mounds. It was shown that satellite altimetry, which was applied for the first time in permafrost zone in the framework of Russian-French project CAR-WET-SIB, is a prospective method to study lakes and khasyreis state and dynamic. References [1] Kirpotin S.N., Naumov A .V., Vorobiov S.N., Mironycheva-Tokareva N.P., Kosych N.P., Lapshina E.D., Marquand J., Kulizhski S.P., Bleuten W. 2007. Western-Siberian Peatlands: Indicators of Climate Change and Their Role in Global Carbon Balance. Chapter 33 in Climate Change and Terrestrial Carbon Sequestration in Central Asia / edited by R.Lal, M.Suleimenov, B.A.Stewart, D.O.Hansen, and P.Doraiswamy, Taylor and Francis, Amsterdam, Holland, pp. 453-472. [2] Kirpotin S., Polishchuk Yu., Zakharova E., Shirokova L., Pokrovsky O., Kolmakova M., Dupre B. 2008. One of Possible Mechanisms of Thermokarst Lakes Drainage in West-Siberian North // International Journal of Environmental Studies. Vol.65, No 5, October 2008, 631-635. [3] Smith, L.C., Sheng, Y., McDonald, G.M., Hinzman, L.D. 2005. Disappearing Arctic Lakes, Science, 308, 1429 [4] Hinkel, K.M., Eisner, W.R., Bockheim, J.G., Nelson, F.E., Peterson, K.M., and Dai, X. 2003. Spatial Extent, Age, and Carbon Stoks in Drained Thaw Lake Basins on the Barrow Peninsula. Alaska. Arctic, Antarctic, and Alpine Research, 35, 3, 291-300.
Western Siberia is a large region with mostly flat relief. Most of its territory comprises the wa... more Western Siberia is a large region with mostly flat relief. Most of its territory comprises the watershed of the Ob' river, and much smaller part in the north - watersheds of Nadym, Pur and Taz rivers. Flat relief significantly affects the hydrographical network, creating a multitude of interconnected natural objects - large and small rivers streams, large floodplains, lakes, bogs etc. The region is also abundant with lakes, mainly small ones with surface area less than 1 km2 and depths of 2-5 m. Flooded areas and bogs also act as a buffer zone, providing a dampening "sponge" effect on the water redistribution within the river system. Large area covered by rivers and wetlands results in high rate of evaporation compared to any other large boreal watershed. Contrasting processes are occurring in the Southern and Northern parts of the Western Siberian Plain. In the south, bogs are expanding in the taiga zone and there is progressive swamping which leads to forest death. These bogs act as a carbon sink due to carbon sequestration in their peat layers. Among the bogs of this part of Western Siberia there is the Great Vasiugan Bog - world's largest peatland with a total area of 6.78 million hectares. Bogs of Vasyugan have appeared about 10 000 years ago and since then are constantly growing. 75% of the actual surface of the Great Vasyugan Bog have appeared during the last 500 years. The situation in the northern part (affected by permafrost) is different. The bogs there are reducing their surface and the forest-tundra regions are being subjected to thermokarst activity and colonisation of bogs by trees. Two contrast processes are observed here - a) increase of lake surface due to melting of lakes' coasts, and b) decrease of surface area or disappearance of lakes due to water drain downstream the hydrological network. We combine in situ observations with satellite remote sensing to monitor hydrological regime of the Western Siberian wetlands. Radar altimetry (TOPEX/Poseidon, Jason-1, GFO, ENVISAT), radiometry (SMMR, SSM/I), optical data (Landsat) and space gravimetry data (GRACE) are used in combination with the in situ observations and the recent field studies done in the August 2008. We present the variability of water level (from radar altimetry) and surface properties (from altimeter waveforms parameters) for the region of Nadym, Pur and Taz rivers, as well as for Vasyugan bog. Seasonal and interannual variability of water abundance is studied using radar altimetry, radiometry, and gravimetry. We also use active and passive microwave observations (radar altimeters and radiometers) to analyse internannual variability ice formation and break-up dates along the Ob' river, which is frozen for more than 7 month in the north and for 5-7 month in the south. This research has been done in the framework of the Russian-French cooperation GDRI "CAR-WET-SIB" and French ANR "IMPACT-Boreal" project.
Accurate and continuous monitoring of lakes and inland seas is possible since 1991 thanks to the ... more Accurate and continuous monitoring of lakes and inland seas is possible since 1991 thanks to the recent missions of satellite altimetry (Topex-Poseidon, ERS-1, ERS-2, Jason-1 and Envisat). Global processing of the data of these satellites could provide temporal and spatial times series of lakes water level from 1991 to 2003 on the whole Earth with a decimeter precision. The response of water level to regional hydrology is particularly marked for lakes and inland seas of semi-arid regions. Altimetry data can provide an invaluable source of information in hydrology sciences, but insitu data (rivers runoff, temperature, precipitation etc.) are still strongly needed to study the evolution of water mass balance of each lake. Moreover, sea level variations that result from variation of hydrological parameters such as river discharge, precipitation and evaporation, are very sensitive indicators of regional climate variations. Recent results obtained on Aral Sea and Issykkul Lake are presented here. Inter — annual changes of water level have been obtained over these lakes that must be interpreted in term of hydrological water balance. Since 1960 the Aral sea has been drying and since 1989 it is divided into two lakes that follow different evolution, the Big Aral in the south which continuously dried up the last 10 years, while the so- called Small Aral in the north presented large inter-annual fluctuations related to constructions and destructions of a dam in the Berg’s strait retaining the water from the Syr Darya. For Issykkul, a slow decrease of the level has been observed over the last hundreds years (4 cm / year), followed by an abrupt and bigger increase of the level of around 10 cm/yr since 1998. The impact on local populations and infra-structures of these fluctuations are dramatic in the case of Aral, much less in the case of Issykkul, but comparative study of both water bodies may help in the future to understand the respective consequences of human-induced activities from the natural changes. It is also the task of a new project recently submitted and accepted by the NATO with scientists from Uzbekistan and Kyrgyz Republic.
We show how the studies of ice and snow cover of continental water bodies can benefit from the sy... more We show how the studies of ice and snow cover of continental water bodies can benefit from the synergy of more than 15 years-long simultaneous active (radar altimeter) and passive (radiometer) observations from radar altimetric satellites (TOPEX/Poseidon, Jason-1, ENVISAT and Geosat Follow-On) and how this approach can be complemented by SSM/I passive microwave data to improve spatial and temporal coverage. Five largest Eurasian continental water bodies—Caspian and Aral seas, Baikal, Ladoga and Onega lakes are selected as examples. First we provide an overview of ice regime and history of ice studies for these seas and lakes. Then a summary of the existing state of the art of ice discrimination methodology from altimetric observations and SSM/I is given. The drawbacks and benefits of each type of sensor and particularities of radiometric properties for each of the chosen water bodies are discussed. Influence of sensor footprint size, ice roughness and snow cover on satellite measurements is also addressed. A step-by-step ice discrimination approach based on a combined use of the data from the four altimetric missions and SSM/I is presented, as well as validation of this approach using in situ and independent satellite data in the visible range. The potential for measurement of snow depth on ice from passive microwave observations using both altimeters and SSM/I is addressed and a qualitative comparison of in situ snow depth observations and satellite-derived estimates is made.
We address spatial and temporal variability of ice conditions in the Aral Sea from historical obs... more We address spatial and temporal variability of ice conditions in the Aral Sea from historical observations and recent satellite microwave observations. A short description of the historical evolution of the Aral Sea since the mid-twentieth century is given, as well as recent activities related to the dam in the Berg strait. An overview of historical observations of the ice regime at the coastal stations and using aerial surveys is provided. The lack of reliable in situ measurements and time series for ice cover parameters since the mid-1980s may be successfully overcome by using active and passive microwave satellite observations, which provide reliable, regular, frequent, and weather-independent data. An ice discrimination methodology, based on the synergy of active and passive data from radar altimeters TOPEX/Poseidon, Jason-1, ENVISAT and Geosat Follow-On (GFO) satellites, as well as the SMMR and SSM/I radiometers is presented. This methodology has been applied to the entire satellite dataset to define specific dates of ice events (first appearance of ice, formation of stable ice cover, appearance of open water and the complete disappearance of ice) for both the Small Aral and Eastern Large Aral. The resulting time series of ice cover parameters are analysed in the context of available in situ observations. First we complement historical observations by satellite imagery in the visible range to illustrate spatial patterns in ice formation, development and decay prior to the late 1980s and in recent time. Then we address interannual variability of timing of ice events and severity of ice conditions since the earliest coastal observations (1940s) until now (2006/2007). Finally, we discuss temporal variability of ice regime parameters in the context of air temperature, bottom morphology and salinity changes.
The Aral Sea has drastically shrunk over the past 50 years, largely due to water withdrawal from ... more The Aral Sea has drastically shrunk over the past 50 years, largely due to water withdrawal from the Amudarya and Syrdarya rivers for land irrigation. If one were to look back over the Holocene,1 the paleolimnology of the Aral Sea is however already marked by the occurrence of several phases of regression and transgression. They resulted partly from climate change, for tectonic reasons, and over the last 2,000 years anthropogenic actions also played a role. After a short review of the paleohistory of the Aral Sea, we will focus on a description of the causes and magnitude of episodes of historical (last 100 years) Aral Sea level variability. The Aral Sea has been marked since the middle of the last century by a process of desiccation due to increase of water intake from the Amudarya and Syrdarya rivers for agricultural purposes. This led to the separation of the Aral Sea into two (in 1986–1987) and then four (in 2009) water bodies. Measurements of Aral Sea water level and surface and water balance were carried out by both in situ gauges and remote-sensing satellite data. This allows for a better understanding of the seasonal, interannual, and decadal trend in Aral Sea water storage variations.
Lake ice grows steadily between the end of freeze-up period and the onset of break-up period as a... more Lake ice grows steadily between the end of freeze-up period and the onset of break-up period as a result of the thermodynamics of freezing water as well as dynamic ice motion on the surface. In thermodynamic thickening, the conductive heat flow controls the ice growth rate and the ice thickness, and the ice thickens downward as a result of heat loss at the top of the ice cover. There has been some demonstration of the potential of brightness temperature from passive microwave airborne radiometers to estimate ice thickness. The value of passive microwave and radar altimeter data from current satellite missions merits to be examined in this respect. The major objective of this study was estimate ice thickness from brightness temperature (TB) at 10.65 and 18.70 GHz from AMSR-E channels and the 19.35 GHz frequency channel from SSM/I on large lakes of the Northern Hemisphere (e.g. Great Bear Lake, Great Slave Lake, Lake Baikal). The evolution of horizontally and vertically polarized TB derived from AMSR-E level 2A raw brightness temperature and EASE Grid Level-3 SSM/I products was compared with ice thicknesses obtained with a previously validated thermodynamic lake ice model and in situ observations over the course of seven winter seasons (2002 and 2009), as well as with recent estimates from the Jason-2 Ku-band radar altimeter data (since 2008). Results show that both passive microwave and radar altimeter data acquired in the 10-19 GHz frequency range offer a promising means for estimating ice thickness from large northern lakes.
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Papers by Alexei Kouraev