Autumn temperatures are at a record 5º C above normal, due to the major loss of sea ice in recent... more Autumn temperatures are at a record 5º C above normal, due to the major loss of sea ice in recent years which allows more solar heating of the ocean. Winter and springtime temperatures remain relatively warm over the entire Arctic, in contrast to the 20th century and consistent with an emerging global warming influence. The year 2007 was the warmest on record for the Arctic, continuing a general, Arctic-wide warming trend that began in the mid-1960s (Fig. A1). Figure A1. Arctic-wide annual averaged surface air temperature anomalies (60°-90°N) based on land stations north of 60°N relative to the 1961-90 mean. From the CRUTEM 3v dataset, (available online at www.cru.uea.ac.uk/cru/data/temperature/. Note this curve does not include ship observations. The summers of 2005 through 2007 all ended with extensive areas of open water (see sea ice section). This allowed extra heat to be absorbed by the ocean from solar radiation. As a result ice freeze-up occurred later than usual in these years. Surface air temperature (SAT) remained high
The annually averaged Arctic Oscillation index (AO, a measure of the strength of circumpolar wind... more The annually averaged Arctic Oscillation index (AO, a measure of the strength of circumpolar winds) was slightly positive in 2006, continuing the trend of a relatively low and fluctuating index which began in the mid-1990s (Figure A1). This follows a strong, persistent positive pattern from 1989 to 1995. The current characteristics of the AO are more consistent with the characteristics of the period from the 1950s to the 1980s, when the AO switched frequently between positive and negative phases. Initial data from 2007 shows a positive AO pattern
ABSTRACT The Arctic, including Alaska, is currently experiencing an unprecedented degree of envir... more ABSTRACT The Arctic, including Alaska, is currently experiencing an unprecedented degree of environmental change. Increases in both the mean annual surface temperature and precipitation have been observed. The combination of the recent increase in air temperature and precipitation have led to "unstable" or "warm" permafrost conditions. This warm and unstable permafrost condition is particularly sensitive to changes in both the surface energy and water balances. The observed climatic changes are expected to continue into the next century. As such, most of the current or expected changes (related to climate, permafrost, and vegetation distributions) will be experienced in areas underlain with warm, unstable permafrost. Themokarst topography forms whenever ice-rice permafrost thaws and the ground subsides into the resulting voids. Extensive areas of active thermokarst activity are currently being observed in these warm, unstable permafrost environments. The important processes involved with thermokarsting include surface ponding, surface subsidence, changes in drainage patterns and related erosion. In this study, we will present a conceptual model of the development of thermokarst features, emphasizing the resulting feedbacks and connections between hydrologic processes and a dynamic surface topography.
Projected increases in air temperature and precipitation due to climate change in Arctic wetlands... more Projected increases in air temperature and precipitation due to climate change in Arctic wetlands could dramatically affect ecosystem function. As a consequence, it is important to define controls on evapotranspiration, the major pathway of water loss from these systems. We quantified the multi-year controls on midday Arctic coastal wetland evapotranspiration, measured with the eddy covariance method at two vegetated, drained thaw lake basins near Barrow, Alaska. Variations in near-surface soil moisture and atmospheric vapor pressure deficits were found to have nonlinear effects on midday evapotranspiration rates. Vapor pressure deficits (VPD) near 0.3 kPa appeared to be an important hydrological threshold, allowing latent heat flux to persistently exceed sensible heat flux. Dry (compared to wet) soils increased bulk surface resistance (water-limited). Wet soils favored ground heat flux and therefore limited the energy available to sensible and latent heat flux (energy-limited). Thus, midday evapotranspiration was suppressed from both dry and wet soils but through different mechanisms. We also found that wet soils (ponding excluded) combined with large VPD, resulted in an increased bulk surface resistance and therefore suppressing evapotranspiration below its potential rate (Priestley-Taylor α < 1.26). This was likely caused by the limited ability of mosses to transfer moisture during large atmospheric demands. Ultimately, in addition to net radiation, the various controlling factors on midday evapotranspiration (i.e., near-surface soil moisture, atmospheric vapor pressure,
The Arctic climate is changing. Permafrost is warming, hydrological processes are changing and bi... more The Arctic climate is changing. Permafrost is warming, hydrological processes are changing and biological and social systems are also evolving in response to these changing conditions. Knowing how the structure and function of arctic terrestrial ecosystems are responding to recent and persistent climate change is paramount to understanding the future state of the Earth system and how humans will need to adapt. Our holistic review presents a broad array of evidence that illustrates convincingly; the Arctic is undergoing a system-wide response to an altered climatic state. New extreme and seasonal surface climatic conditions are being experienced, a range of biophysical states and processes influenced by the threshold and phase change of freezing point are being altered, hydrological and biogeochemical cycles are shifting, and more regularly human sub-systems are being affected. Importantly, the patterns, magnitude and mechanisms of change have sometimes been unpredictable or difficult to isolate due to compounding factors. In almost every discipline represented, we show
Permafrost temperatures in boreholes displayed a 2 4◦C increase over the last 50-100 years on the... more Permafrost temperatures in boreholes displayed a 2 4◦C increase over the last 50-100 years on the North Slope of Alaska and there was a concurrent warming of discontinuous permafrost. Long-term monitoring of deep wells in a north/south transect across the North Slope of Alaska reveals variable warming with some cooling periods, over the last twenty five years; this is consistent with the broader-scale trends in air temperatures observed in northern Alaska. Discontinuous permafrost is warming and thawing and extensive areas of thermokarst terrain (marked subsidence of the surface resulting from thawing of ice-rich permafrost) are now developing as a result of climatic change. Thawing permafrost and thermokarst have been observed at several sites in Interior Alaska. Thermokarst is developing in the boreal forests of Alaska where ice-rich discontinuous permafrost is thawing. Thawing destroys the physical foundation (ice-rich soil) on which forests develop, causing dramatic changes in t...
A valuable input to crop growth and yield models would be estimates of current crop condition. If... more A valuable input to crop growth and yield models would be estimates of current crop condition. If multispectral reflectance indicates crop condition, then remote sensing may provide an additional tool for crop assessment. The effects of nitrogen fertilization on the spectral reflectance and agronomic characteristics of winter wheat (Triticum aestivum L.) were determined through field experiments. Spectral reflectance was measured during the 1979 and 1980 growing seasons with a spectroradiometer. Agronomic data included total leaf N concentration, leaf chlorophyll concentration, stage of development, leaf area index (LAI), plant moisture, and fresh and dry phytomass. Nitrogen deficiency caused increased visible, reduced near infrared, and increased middle infrared reflectance. These changes were related to lower levels of chlorophyll and reduced leaf area in the N-deficient plots. Green LAI, an important descriptor of wheat canopies, could be reliably estimated with multispectral dat...
Lakes are important water resources on the North Slope of Alaska. Oilfield exploration and produc... more Lakes are important water resources on the North Slope of Alaska. Oilfield exploration and production requires water for facility use as well as transportation. Ice road construction requires winter extraction of fresh water. Since most North Slope lakes are relatively shallow, the quantity and quality of the water remaining under the ice by the end of the winter are important
ABSTRACT Area underlain by permafrost in Alaska varies from continuous in the north through spora... more ABSTRACT Area underlain by permafrost in Alaska varies from continuous in the north through sporadic and warmer ground in the south. A changing climate makes estimating thermal response and predicting changes in extent in the transitional areas valuable for wildlife management as well as human infrastructure resiliency. Out recent research has focused on the Seward Peninsula of Alaska. Where average air temperatures are just below freezing and the permafrost is very warm, an area susceptible to dramatic change in response to a warming climate. In this paper the focus expands to the state of Alaska using two methods of estimating extent: the Geophysical Institute Permafrost Lab method (GIPL model is based on the modified Kudryavtsev approach) and the TTOP method originally derived by Smith and Riseborough. Current meteorological data is based on the present observational record.
ABSTRACT The soil moisture regime in the sub-arctic environment plays an important role in a numb... more ABSTRACT The soil moisture regime in the sub-arctic environment plays an important role in a number of processes related to climate change including soil respiration, permafrost distribution, and the frequency and severity of wildfires. In order to understand and predict ecosystem response to a changing climate and resulting feedbacks, it is critical to quantify the interaction of soil moisture and meteorology as a function of climatic processes, landscape type, and vegetation. The primary of goal of our research is to develop/modify a numerical model, which is able to describe, simulate, and predict soil moisture dynamics and all other hydrologic processes everywhere throughout a sub-arctic watershed. This model will be used as a tool to better understand the effects of vegetation and soil type, presence of permafrost, amount and timing of precipitation, and disturbance (such as wildfire) on soil moisture dynamics. The area selected for this research is the Caribou-Poker Creeks Research Watershed (CPCRW), located 48 km north of Fairbanks, Alaska (65° 10&#39;N, 147° 30&#39;W) and encompasses and area of 101.5 km2. Permafrost in CPCRW is discontinuous, generally found along north facing slopes and valley bottoms. Three small sub-basins of CPCRW, which are underlain with approximately 3, 19, and 53% permafrost, are simulated to explore differences in permafrost vs. non-permafrost dominated areas. The Arctic Hydrological and Thermal Process Model (ARHYTHM) is a process based, physically distributed numeric model will be modified to simulate the hydrologic processes throughout a watershed underlain by discontinuous permafrost. The model can be used as a tool to simulate spatially distributed processes, such as soil moisture dynamics or snowmelt, as well as point measurements such as streamflow at any point within the model domain. ARHYTHM was developed to simulate energy and mass transfer processes in the Alaskan arctic regions. Modifications made to the ARHYTHM model will be made to reflect the differences between the sub-arctic and arctic environments. Changes to the model will include the representation of discontinuous permafrost, distributed vegetation types, and the incorporation of a deep groundwater component. The model domain is based upon a 100-meter digital elevation model (DEM) that encompasses CPCRW. Parameters such as soil type and depth, vegetation type, and permafrost distribution (as well as their hydrologic properties) will be spatially distributed throughout the model domain. Meteorologic data (radiation components, relative humidity, air and ground temperature, precipitation, and wind speed) are used to drive the model. This paper will present up-to-date results of this on-going research.
ABSTRACT Much of the Alaskan Arctic and Subarctic receives a minimal amount of annual precipitati... more ABSTRACT Much of the Alaskan Arctic and Subarctic receives a minimal amount of annual precipitation. Changes to regional precipitation patterns and the general transient warming expected in the next century&#39;s lake hydrology and the associated wetlands place the risk of lakes perforating the permafrost boundary on the forefront. Lake change on the Alaskan landscape due to permafrost degradation is going to be important to local ecosystems and in, for example, providing habitat for migratory waterfowl in the next decades and centuries. Permafrost presence, absence, and thickness are interconnected in the deciphering of groundwater gradients and projection of surface water presence, absence, disappearance, and appearance on the Alaskan landscape. Detailed efforts have been made to produce datasets of presence or absence of the permafrost on the Seward Peninsula and further efforts are in place to do the same for the entire state. Continuous permafrost can provide an impervious barrier to groundwater movement and most groundwater-surface water interaction occurs in areas of discontinuous permafrost. With permafrost thawing and open talik formation in discontinuous permafrost regions, surface water formerly perched above the permafrost can drain into the subpermafrost groundwater. In contrast, in areas where the local hydraulic gradient is upwards, subpermafrost groundwater may discharge at the surface as the confining layer of permafrost degrades and an open talik forms. Lake change, in the absence of changes in evaporation and surface flow, are governed by the local vertical flux of water. In this study we compile observations of surface water storage change in Alaska and conjecture that shrinking/ disappearing lakes are evidence of supra-permafrost groundwater downwelling. The resulting dataset serves as verification for our model of groundwater dynamics. The planned method for determining the ground water gradient and degree to which vertical percolation will be restricted is to analyze digital terrain information with hydrology, permafrost, soils, geology, and current climate data. To start the groundwater gradient computations we will focus on areas with known hydrologic phenomena and elaborate on a vector based gradient map referencing the steepness of the terrain and the precipitation on the surrounding higher elevations. Once the present groundwater and surface water situation is captured, based on the future subsidence of the permafrost in areas on the landscape, we propose to forecast the wetness and dryness across Alaska, capturing the uniqueness of each watershed&#39;s turn toward wetter and then drier over the next decades and centuries.
ABSTRACT The Water Balance Simulation Model ETH, WaSiM-ETH, is a deterministic, spatially distrib... more ABSTRACT The Water Balance Simulation Model ETH, WaSiM-ETH, is a deterministic, spatially distributed hydrological model that has been successfully applied to numerous basins ranging from tropical rainforests in Asia to Alpine regions in Europe. This is the first time WaSiM-ETH is applied to the Arctic. Until now, the model has been lacking an active layer algorithm that is essential to successfully simulate the hydrologic regime in permafrost regions. Although the long-term goal of WaSiM-ETH is to dynamically couple the thermal and hydrological regimes, we implemented a simple empiric formula alpha*sqrt(snowfreedays) to represent the seasonal freezing and thawing of the active layer. The count of snow-free-days starts as soon as the snow water equivalent decreases below a defined value. If fresh snow falls, then two things can happen: 1) increasing the counter for snow free days will be paused until the snow melts away within a defined period. The snow free days are increased normally once the snow cover is ablated. 2) If the snow cover lasts for more than a specified time, the snow-free-days counter is reset to zero thus setting the thaw depth to zero. The latter is the simple refreezing model. We applied the model to an intensively studied wetland in northern Alaska that has all portions of the water balance measured. The watershed is mainly represented by a drained thaw lake basin and hence, exhibit low hydraulic gradients with the main topographical features formed by high and low centered polygons. Evapotranspiration (ET) represents the major pathway of water loss from the wetland despite several ET-limiting factors. Through its dynamic linkage between soil moisture and evaporation, WaSiM-ETH allows for a realistic representation of evaporation from the moss dominated wetland that experiences increased canopy resistance in late summer. WaSiM-ETH has a surface routing scheme that takes into account ponds as well as small scale topography that are typical features in the area. Lateral flows exhibit a strong seasonal variation with peak flow during snowmelt. The modeling of lateral flow is complicated by the disconnection of the early season flow paths, leaving most low centered polygons as individual hydrologic units a week after snow melt. We present a validation of the modified WaSiM-ETH on measured runoff, evapotranspiration and spatially distributed water table elevations from an arctic watershed underlain by permafrost. Our aim is to reduce the uncertainty in water table projections at finer scales (
ABSTRACT The framework of the International Polar Decade (IPD) could support cooperation, data sh... more ABSTRACT The framework of the International Polar Decade (IPD) could support cooperation, data sharing and collaboration needed to understand the rapidly changing polar environment. The Arctic is experiencing rapid transitions in the atmosphere, the terrestrial regions and in the Arctic Ocean, perhaps greater than has been observed in recorded history. We were fortunate to convene the beginning of the Fourth International Polar Year (IPY) at the same time we experienced a record low in summer sea ice extent in the Arctic Ocean. This serendipitous occurrence of enhanced and coordinated observations at a time when a record minimum occurred focused public attention on the polar regions and permitted higher level system analyses that would not otherwise have been possible. The international commitment towards dense observations of the Arctic Ocean during IPY led to comprehensive documentation of the record sea ice minimum and its aftermath and repercussions throughout the Arctic system. Many other cryospheric processes are also changing on relatively rapid time scales, but these may not be statistically significant or even consistent over the short time frame of the IPY. In order to document and understand the system-scale changes occurring in high latitudes, it is necessary to engage in longer-term observations and analyses. Many of these processes display a very small or subtle signal of climate warming amidst the noise of large inherent variability. Although precipitation in the form of snow is projected to increase, that change is difficult to document due to very large year to year variability. Permafrost is warming in most places throughout the Arctic, but in many cases that change is on the order of tenths of a degree per decade. Although we can project trends in variables, the consequences and interactions between variables are more difficult to reliably document. In order to more confidently predict interactions between processes, and to quantitatively describe the mechanisms associated with critically important feedback processes, we must invest in long-term monitoring. We must maintain observations and conduct synthetic analyses on the many inter-dependent processes that collectively comprise the polar systems. Defined intensive observation periods with agreed-upon temporal and spatial extent during the IPD is appropriate to help focus these efforts. Regional studies, such as comparative analyses of the Barents and Bering Seas would provide a contextual framework for promoting international collaboration. Thematic studies, such as quantifying changes in circumpolar precipitation regimes, would focus efforts upon particularly problematic challenges.
Autumn temperatures are at a record 5º C above normal, due to the major loss of sea ice in recent... more Autumn temperatures are at a record 5º C above normal, due to the major loss of sea ice in recent years which allows more solar heating of the ocean. Winter and springtime temperatures remain relatively warm over the entire Arctic, in contrast to the 20th century and consistent with an emerging global warming influence. The year 2007 was the warmest on record for the Arctic, continuing a general, Arctic-wide warming trend that began in the mid-1960s (Fig. A1). Figure A1. Arctic-wide annual averaged surface air temperature anomalies (60°-90°N) based on land stations north of 60°N relative to the 1961-90 mean. From the CRUTEM 3v dataset, (available online at www.cru.uea.ac.uk/cru/data/temperature/. Note this curve does not include ship observations. The summers of 2005 through 2007 all ended with extensive areas of open water (see sea ice section). This allowed extra heat to be absorbed by the ocean from solar radiation. As a result ice freeze-up occurred later than usual in these years. Surface air temperature (SAT) remained high
The annually averaged Arctic Oscillation index (AO, a measure of the strength of circumpolar wind... more The annually averaged Arctic Oscillation index (AO, a measure of the strength of circumpolar winds) was slightly positive in 2006, continuing the trend of a relatively low and fluctuating index which began in the mid-1990s (Figure A1). This follows a strong, persistent positive pattern from 1989 to 1995. The current characteristics of the AO are more consistent with the characteristics of the period from the 1950s to the 1980s, when the AO switched frequently between positive and negative phases. Initial data from 2007 shows a positive AO pattern
ABSTRACT The Arctic, including Alaska, is currently experiencing an unprecedented degree of envir... more ABSTRACT The Arctic, including Alaska, is currently experiencing an unprecedented degree of environmental change. Increases in both the mean annual surface temperature and precipitation have been observed. The combination of the recent increase in air temperature and precipitation have led to &quot;unstable&quot; or &quot;warm&quot; permafrost conditions. This warm and unstable permafrost condition is particularly sensitive to changes in both the surface energy and water balances. The observed climatic changes are expected to continue into the next century. As such, most of the current or expected changes (related to climate, permafrost, and vegetation distributions) will be experienced in areas underlain with warm, unstable permafrost. Themokarst topography forms whenever ice-rice permafrost thaws and the ground subsides into the resulting voids. Extensive areas of active thermokarst activity are currently being observed in these warm, unstable permafrost environments. The important processes involved with thermokarsting include surface ponding, surface subsidence, changes in drainage patterns and related erosion. In this study, we will present a conceptual model of the development of thermokarst features, emphasizing the resulting feedbacks and connections between hydrologic processes and a dynamic surface topography.
Projected increases in air temperature and precipitation due to climate change in Arctic wetlands... more Projected increases in air temperature and precipitation due to climate change in Arctic wetlands could dramatically affect ecosystem function. As a consequence, it is important to define controls on evapotranspiration, the major pathway of water loss from these systems. We quantified the multi-year controls on midday Arctic coastal wetland evapotranspiration, measured with the eddy covariance method at two vegetated, drained thaw lake basins near Barrow, Alaska. Variations in near-surface soil moisture and atmospheric vapor pressure deficits were found to have nonlinear effects on midday evapotranspiration rates. Vapor pressure deficits (VPD) near 0.3 kPa appeared to be an important hydrological threshold, allowing latent heat flux to persistently exceed sensible heat flux. Dry (compared to wet) soils increased bulk surface resistance (water-limited). Wet soils favored ground heat flux and therefore limited the energy available to sensible and latent heat flux (energy-limited). Thus, midday evapotranspiration was suppressed from both dry and wet soils but through different mechanisms. We also found that wet soils (ponding excluded) combined with large VPD, resulted in an increased bulk surface resistance and therefore suppressing evapotranspiration below its potential rate (Priestley-Taylor α < 1.26). This was likely caused by the limited ability of mosses to transfer moisture during large atmospheric demands. Ultimately, in addition to net radiation, the various controlling factors on midday evapotranspiration (i.e., near-surface soil moisture, atmospheric vapor pressure,
The Arctic climate is changing. Permafrost is warming, hydrological processes are changing and bi... more The Arctic climate is changing. Permafrost is warming, hydrological processes are changing and biological and social systems are also evolving in response to these changing conditions. Knowing how the structure and function of arctic terrestrial ecosystems are responding to recent and persistent climate change is paramount to understanding the future state of the Earth system and how humans will need to adapt. Our holistic review presents a broad array of evidence that illustrates convincingly; the Arctic is undergoing a system-wide response to an altered climatic state. New extreme and seasonal surface climatic conditions are being experienced, a range of biophysical states and processes influenced by the threshold and phase change of freezing point are being altered, hydrological and biogeochemical cycles are shifting, and more regularly human sub-systems are being affected. Importantly, the patterns, magnitude and mechanisms of change have sometimes been unpredictable or difficult to isolate due to compounding factors. In almost every discipline represented, we show
Permafrost temperatures in boreholes displayed a 2 4◦C increase over the last 50-100 years on the... more Permafrost temperatures in boreholes displayed a 2 4◦C increase over the last 50-100 years on the North Slope of Alaska and there was a concurrent warming of discontinuous permafrost. Long-term monitoring of deep wells in a north/south transect across the North Slope of Alaska reveals variable warming with some cooling periods, over the last twenty five years; this is consistent with the broader-scale trends in air temperatures observed in northern Alaska. Discontinuous permafrost is warming and thawing and extensive areas of thermokarst terrain (marked subsidence of the surface resulting from thawing of ice-rich permafrost) are now developing as a result of climatic change. Thawing permafrost and thermokarst have been observed at several sites in Interior Alaska. Thermokarst is developing in the boreal forests of Alaska where ice-rich discontinuous permafrost is thawing. Thawing destroys the physical foundation (ice-rich soil) on which forests develop, causing dramatic changes in t...
A valuable input to crop growth and yield models would be estimates of current crop condition. If... more A valuable input to crop growth and yield models would be estimates of current crop condition. If multispectral reflectance indicates crop condition, then remote sensing may provide an additional tool for crop assessment. The effects of nitrogen fertilization on the spectral reflectance and agronomic characteristics of winter wheat (Triticum aestivum L.) were determined through field experiments. Spectral reflectance was measured during the 1979 and 1980 growing seasons with a spectroradiometer. Agronomic data included total leaf N concentration, leaf chlorophyll concentration, stage of development, leaf area index (LAI), plant moisture, and fresh and dry phytomass. Nitrogen deficiency caused increased visible, reduced near infrared, and increased middle infrared reflectance. These changes were related to lower levels of chlorophyll and reduced leaf area in the N-deficient plots. Green LAI, an important descriptor of wheat canopies, could be reliably estimated with multispectral dat...
Lakes are important water resources on the North Slope of Alaska. Oilfield exploration and produc... more Lakes are important water resources on the North Slope of Alaska. Oilfield exploration and production requires water for facility use as well as transportation. Ice road construction requires winter extraction of fresh water. Since most North Slope lakes are relatively shallow, the quantity and quality of the water remaining under the ice by the end of the winter are important
ABSTRACT Area underlain by permafrost in Alaska varies from continuous in the north through spora... more ABSTRACT Area underlain by permafrost in Alaska varies from continuous in the north through sporadic and warmer ground in the south. A changing climate makes estimating thermal response and predicting changes in extent in the transitional areas valuable for wildlife management as well as human infrastructure resiliency. Out recent research has focused on the Seward Peninsula of Alaska. Where average air temperatures are just below freezing and the permafrost is very warm, an area susceptible to dramatic change in response to a warming climate. In this paper the focus expands to the state of Alaska using two methods of estimating extent: the Geophysical Institute Permafrost Lab method (GIPL model is based on the modified Kudryavtsev approach) and the TTOP method originally derived by Smith and Riseborough. Current meteorological data is based on the present observational record.
ABSTRACT The soil moisture regime in the sub-arctic environment plays an important role in a numb... more ABSTRACT The soil moisture regime in the sub-arctic environment plays an important role in a number of processes related to climate change including soil respiration, permafrost distribution, and the frequency and severity of wildfires. In order to understand and predict ecosystem response to a changing climate and resulting feedbacks, it is critical to quantify the interaction of soil moisture and meteorology as a function of climatic processes, landscape type, and vegetation. The primary of goal of our research is to develop/modify a numerical model, which is able to describe, simulate, and predict soil moisture dynamics and all other hydrologic processes everywhere throughout a sub-arctic watershed. This model will be used as a tool to better understand the effects of vegetation and soil type, presence of permafrost, amount and timing of precipitation, and disturbance (such as wildfire) on soil moisture dynamics. The area selected for this research is the Caribou-Poker Creeks Research Watershed (CPCRW), located 48 km north of Fairbanks, Alaska (65° 10&#39;N, 147° 30&#39;W) and encompasses and area of 101.5 km2. Permafrost in CPCRW is discontinuous, generally found along north facing slopes and valley bottoms. Three small sub-basins of CPCRW, which are underlain with approximately 3, 19, and 53% permafrost, are simulated to explore differences in permafrost vs. non-permafrost dominated areas. The Arctic Hydrological and Thermal Process Model (ARHYTHM) is a process based, physically distributed numeric model will be modified to simulate the hydrologic processes throughout a watershed underlain by discontinuous permafrost. The model can be used as a tool to simulate spatially distributed processes, such as soil moisture dynamics or snowmelt, as well as point measurements such as streamflow at any point within the model domain. ARHYTHM was developed to simulate energy and mass transfer processes in the Alaskan arctic regions. Modifications made to the ARHYTHM model will be made to reflect the differences between the sub-arctic and arctic environments. Changes to the model will include the representation of discontinuous permafrost, distributed vegetation types, and the incorporation of a deep groundwater component. The model domain is based upon a 100-meter digital elevation model (DEM) that encompasses CPCRW. Parameters such as soil type and depth, vegetation type, and permafrost distribution (as well as their hydrologic properties) will be spatially distributed throughout the model domain. Meteorologic data (radiation components, relative humidity, air and ground temperature, precipitation, and wind speed) are used to drive the model. This paper will present up-to-date results of this on-going research.
ABSTRACT Much of the Alaskan Arctic and Subarctic receives a minimal amount of annual precipitati... more ABSTRACT Much of the Alaskan Arctic and Subarctic receives a minimal amount of annual precipitation. Changes to regional precipitation patterns and the general transient warming expected in the next century&#39;s lake hydrology and the associated wetlands place the risk of lakes perforating the permafrost boundary on the forefront. Lake change on the Alaskan landscape due to permafrost degradation is going to be important to local ecosystems and in, for example, providing habitat for migratory waterfowl in the next decades and centuries. Permafrost presence, absence, and thickness are interconnected in the deciphering of groundwater gradients and projection of surface water presence, absence, disappearance, and appearance on the Alaskan landscape. Detailed efforts have been made to produce datasets of presence or absence of the permafrost on the Seward Peninsula and further efforts are in place to do the same for the entire state. Continuous permafrost can provide an impervious barrier to groundwater movement and most groundwater-surface water interaction occurs in areas of discontinuous permafrost. With permafrost thawing and open talik formation in discontinuous permafrost regions, surface water formerly perched above the permafrost can drain into the subpermafrost groundwater. In contrast, in areas where the local hydraulic gradient is upwards, subpermafrost groundwater may discharge at the surface as the confining layer of permafrost degrades and an open talik forms. Lake change, in the absence of changes in evaporation and surface flow, are governed by the local vertical flux of water. In this study we compile observations of surface water storage change in Alaska and conjecture that shrinking/ disappearing lakes are evidence of supra-permafrost groundwater downwelling. The resulting dataset serves as verification for our model of groundwater dynamics. The planned method for determining the ground water gradient and degree to which vertical percolation will be restricted is to analyze digital terrain information with hydrology, permafrost, soils, geology, and current climate data. To start the groundwater gradient computations we will focus on areas with known hydrologic phenomena and elaborate on a vector based gradient map referencing the steepness of the terrain and the precipitation on the surrounding higher elevations. Once the present groundwater and surface water situation is captured, based on the future subsidence of the permafrost in areas on the landscape, we propose to forecast the wetness and dryness across Alaska, capturing the uniqueness of each watershed&#39;s turn toward wetter and then drier over the next decades and centuries.
ABSTRACT The Water Balance Simulation Model ETH, WaSiM-ETH, is a deterministic, spatially distrib... more ABSTRACT The Water Balance Simulation Model ETH, WaSiM-ETH, is a deterministic, spatially distributed hydrological model that has been successfully applied to numerous basins ranging from tropical rainforests in Asia to Alpine regions in Europe. This is the first time WaSiM-ETH is applied to the Arctic. Until now, the model has been lacking an active layer algorithm that is essential to successfully simulate the hydrologic regime in permafrost regions. Although the long-term goal of WaSiM-ETH is to dynamically couple the thermal and hydrological regimes, we implemented a simple empiric formula alpha*sqrt(snowfreedays) to represent the seasonal freezing and thawing of the active layer. The count of snow-free-days starts as soon as the snow water equivalent decreases below a defined value. If fresh snow falls, then two things can happen: 1) increasing the counter for snow free days will be paused until the snow melts away within a defined period. The snow free days are increased normally once the snow cover is ablated. 2) If the snow cover lasts for more than a specified time, the snow-free-days counter is reset to zero thus setting the thaw depth to zero. The latter is the simple refreezing model. We applied the model to an intensively studied wetland in northern Alaska that has all portions of the water balance measured. The watershed is mainly represented by a drained thaw lake basin and hence, exhibit low hydraulic gradients with the main topographical features formed by high and low centered polygons. Evapotranspiration (ET) represents the major pathway of water loss from the wetland despite several ET-limiting factors. Through its dynamic linkage between soil moisture and evaporation, WaSiM-ETH allows for a realistic representation of evaporation from the moss dominated wetland that experiences increased canopy resistance in late summer. WaSiM-ETH has a surface routing scheme that takes into account ponds as well as small scale topography that are typical features in the area. Lateral flows exhibit a strong seasonal variation with peak flow during snowmelt. The modeling of lateral flow is complicated by the disconnection of the early season flow paths, leaving most low centered polygons as individual hydrologic units a week after snow melt. We present a validation of the modified WaSiM-ETH on measured runoff, evapotranspiration and spatially distributed water table elevations from an arctic watershed underlain by permafrost. Our aim is to reduce the uncertainty in water table projections at finer scales (
ABSTRACT The framework of the International Polar Decade (IPD) could support cooperation, data sh... more ABSTRACT The framework of the International Polar Decade (IPD) could support cooperation, data sharing and collaboration needed to understand the rapidly changing polar environment. The Arctic is experiencing rapid transitions in the atmosphere, the terrestrial regions and in the Arctic Ocean, perhaps greater than has been observed in recorded history. We were fortunate to convene the beginning of the Fourth International Polar Year (IPY) at the same time we experienced a record low in summer sea ice extent in the Arctic Ocean. This serendipitous occurrence of enhanced and coordinated observations at a time when a record minimum occurred focused public attention on the polar regions and permitted higher level system analyses that would not otherwise have been possible. The international commitment towards dense observations of the Arctic Ocean during IPY led to comprehensive documentation of the record sea ice minimum and its aftermath and repercussions throughout the Arctic system. Many other cryospheric processes are also changing on relatively rapid time scales, but these may not be statistically significant or even consistent over the short time frame of the IPY. In order to document and understand the system-scale changes occurring in high latitudes, it is necessary to engage in longer-term observations and analyses. Many of these processes display a very small or subtle signal of climate warming amidst the noise of large inherent variability. Although precipitation in the form of snow is projected to increase, that change is difficult to document due to very large year to year variability. Permafrost is warming in most places throughout the Arctic, but in many cases that change is on the order of tenths of a degree per decade. Although we can project trends in variables, the consequences and interactions between variables are more difficult to reliably document. In order to more confidently predict interactions between processes, and to quantitatively describe the mechanisms associated with critically important feedback processes, we must invest in long-term monitoring. We must maintain observations and conduct synthetic analyses on the many inter-dependent processes that collectively comprise the polar systems. Defined intensive observation periods with agreed-upon temporal and spatial extent during the IPD is appropriate to help focus these efforts. Regional studies, such as comparative analyses of the Barents and Bering Seas would provide a contextual framework for promoting international collaboration. Thematic studies, such as quantifying changes in circumpolar precipitation regimes, would focus efforts upon particularly problematic challenges.
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