EGU General Assembly Conference Abstracts, May 1, 2010
An understanding of the temporal and spatial characteristics of rainfall is central to water reso... more An understanding of the temporal and spatial characteristics of rainfall is central to water resources planning and management. However, such information is often limited in many developing countries like Malawi. In an effort to bridge the information gap, this study examined the temporal and spatial charecteristics of rainfall in Malawi. Rainfall readings from 42 stations across Malawi from 1960 to 2006 were analysed at monthly, annual and seasonal scales. The Malawian rainfall season lasts from November to April. The data were firstly subjected to quality checks through the cumulative deviations test and the Standard Normal Homogeinity Test (SNHT). Monthly distribution in a typical year, called heterogeneity, was investigated using the Precipitation Concentration Index (PCI). Further, normalized precipitation anomaly series of annual rainfall series (AR) and the PCI (APCI) were used to test for interannual rainfall variability. Spatial variability was characterised by fitting the Spatial Correlation function (SCF). The nonparametric Mann-Kendall statistic was used to investigate the temporal trends of the various rainfall variables. The results showed that 40 of the stations passed both data quality tests. For the two stations that failed, the data were adjusted using nearby stations. Annual and seasonal rainfall were found to be characterised by high spatial variation. The country mean annual rainfall was 1095 mm with mean interannual variability of 26%. The highland areas to the north and southeast of the country exhibited the highest rainfall and lowest interannual variability. Lowest rainfall coupled with high interannual variability was found in the Lower Shire basin, in the southern part of Malawi. This simillarity is the pattern of annual and seasonal rainfall should be expected because all stations had over 90% of their observed annual rainfall in the six month period between November and April. Monthly rainfall was found to be highly variable both temporally and spatially. None of the stations have stable monthly rainfall regimes (mean PCI of less than 10). Stations with the highest mean rainfall were found to have a lower interannual variability. The rainfall stations showed low spatial correlations for annual, monthly as well as seasonal timescales indicating that the data may not be suitable for spatial interpolation. However, some structure (i.e. lower correlation with distance) could be observed when aggregating the data at 50 mile intervals. The annual and seasonal rainfall series were dominated by negative trends. The spatial distribution of the trends can be described as heterogeneous, although most of the stations in the southern region have negative trends. At the monthly timescale, 37 of the stations show a negative trend with four of the stations, all in the south, showing significant negative trends. On the other hand, only 5 stations show positive trends with only one significant trend in the south.
In the current human-modified world, or Anthropocene, the state of water stores and fluxes has be... more In the current human-modified world, or Anthropocene, the state of water stores and fluxes has become dependent on human as well as natural processes. Water deficits (or droughts) are the result of a complex interaction between meteorological anomalies, land surface processes, and human inflows, outflows, and storage changes. Our current inability to adequately analyse and manage drought in many places points to gaps in our understanding and to inadequate data and tools. The Anthropocene requires a new framework for drought definitions and research. Drought definitions need to be revisited to explicitly include human processes driving and modifying soil moisture drought and hydrological drought development. We give recommendations for robust drought definitions to clarify timescales of drought and prevent confusion with related terms such as water scarcity and overexploitation. Additionally, our understanding and analysis of drought need to move from single driver to multiple drivers and from uni-directional to multi-directional. We identify research gaps and propose analysis approaches on (1) drivers, (2) modifiers, (3) impacts, (4) feedbacks, and (5) changing the baseline of drought in the Anthropocene. The most pressing research questions are related to the attribution of drought to its causes, to linking drought impacts to drought characteristics, and to societal adaptation and responses to drought. Example questions include Published by Copernicus Publications on behalf of the European Geosciences Union. 3632 A. F. Van Loon et al.: Drought in a human-modified world (i) What are the dominant drivers of drought in different parts of the world? (ii) How do human modifications of drought enhance or alleviate drought severity? (iii) How do impacts of drought depend on the physical characteristics of drought vs. the vulnerability of people or the environment? (iv) To what extent are physical and human drought processes coupled, and can feedback loops be identified and altered to lessen or mitigate drought? (v) How should we adapt our drought analysis to accommodate changes in the normal situation (i.e. what are considered normal or reference conditions) over time? Answering these questions requires exploration of qualitative and quantitative data as well as mixed modelling approaches. The challenges related to drought research and management in the Anthropocene are not unique to drought, but do require urgent attention. We give recommendations drawn from the fields of flood research, ecology, water management, and water resources studies. The framework presented here provides a holistic view on drought in the Anthropocene, which will help improve management strategies for mitigating the severity and reducing the impacts of droughts in future.
Discharge over the Narayani river catchment of Nepal was simulated using Statkraft's Hydrologic F... more Discharge over the Narayani river catchment of Nepal was simulated using Statkraft's Hydrologic Forecasting Toolbox (Shyft) forced with observations and three global forcing datasets: (i) ERA-Interim (ERA-I), (ii) Water and Global Change (WATCH) Forcing Data ERA-I (WFDEI), and (iii) Coordinated Regional Climate Downscaling Experiment with the contributing institute Rossy Centre, Swedish Meteorological and Hydrological Institute (CORDEX-SMHI). Not only does this provide an opportunity to evaluate discharge variability and uncertainty resulting from different forcing data but also it demonstrates the capability and potential of using these global datasets in data-sparse regions. The fidelity of discharge simulation is the greatest when using observations combined with the WFDEI forcing dataset (hybrid datasets). These results demonstrate the successful application of global forcing datasets for regional catchment-scale modeling in remote regions. The results were also promising to provide insight of the interannual variability in discharge. This study showed that while large biases in precipitation can be reduced by applying a precipitation correction factor (p_corr_factor), the best result is obtained using bias-corrected forcing data as input, i.e. the WFDEI outperformed other forcing datasets. Accordingly, the WFDEI forcing dataset holds great potential for improving our understanding of the hydrology of data-sparse Himalayan regions and providing the potential for prediction. The use of CORDEX-SMHI-and ERA-I-derived data requires further validation and bias correction, particularly over the high mountain regions.
This study is a contribution to the northern hemisphere climate processes land surface experiment... more This study is a contribution to the northern hemisphere climate processes land surface experiment (NOPEX). Its purpose is to investigate the spatial variability of groundwater levels and soil moisture content at different scales in a landscape dominated by boreal forest and till soils, which is characteristic of the Nordic countries. The analysis of data from the NOPEX area are based on a review of previous studies on the spatial distribution of these state variables and their signi®cance for runoff formation. Soil moisture content in the unsaturated zone and depth to the groundwater table show characteristic patterns which are related to the landscape elements (patches) of the drainage basins. Similar behaviour is observed in different parts of the NOPEX region. The variability of average values between areas decreases to a minimum for catchments with size larger than 1 km 2. It can therefore be concluded that the main part of the spatial variability of soil moisture content and depth to the groundwater level in the till soils of the NOPEX area is found within small drainage basins. Based on a physical description of the soil, distribution functions of soil moisture content conditioned on the depth to the groundwater table have been developed, both for the patch scale and the catchment scale.
Space–time modelling of catchment scale drought characteristics
Journal of Hydrology, Sep 1, 2009
... Differences in hydrological stores are the main factor controlling drought propagation, leadi... more ... Differences in hydrological stores are the main factor controlling drought propagation, leading to different lag times between meteorological and hydrological drought across space ([van Lanen and Tallaksen, 2007] and [Peters, 2003]). ...
Your article is protected by copyright and all rights are held exclusively by Springer Science +B... more Your article is protected by copyright and all rights are held exclusively by Springer Science +Business Media Dordrecht. This e-offprint is for personal use only and shall not be selfarchived in electronic repositories. If you wish to self-archive your article, please use the accepted manuscript version for posting on your own website. You may further deposit the accepted manuscript version in any repository, provided it is only made publicly available 12 months after official publication or later and provided acknowledgement is given to the original source of publication and a link is inserted to the published article on Springer's website. The link must be accompanied by the following text: "The final publication is available at link.springer.com".
An understanding of the temporal and spatial characteristics of rainfall is central to water reso... more An understanding of the temporal and spatial characteristics of rainfall is central to water resources planning and management. Such information is often limited in many developing countries like Malawi, an agro-based economy where 90% of the agriculture is rain fed. Most climate models project an overall decline of rainfall for the whole Southern Africa. However, some studies have observed changes in the mean rainfall varying on relatively small spatial scales in the region. The main objective of this study was to investigate spatial and temporal characteristics of annual, seasonal and monthly rainfall in Malawi, a relatively lower spatial scale. In Malawi (Fig. 1), both rainfall and temperature are altitude dependent. Rainfall ranges from 700 mm in the semi-arid low lying parts to 2500 mm in the highlands whereas temperature ranges between 10–40oC countrywide. Two main rain bearing systems dominate the rainfall of Malawi and the Southern Africa region: (1) The Inter tropical Conve...
An overall appraisal of runoff changes at the European scale has been hindered by "white space" o... more An overall appraisal of runoff changes at the European scale has been hindered by "white space" on maps of observed trends due to a paucity of readily-available streamflow data. This study tested whether this white space can be filled using estimates of trends derived from model simulations of European runoff. The simulations stem from an ensemble of eight global hydrological models that were forced with the same climate input for the period 1963-2000. The derived trends were validated for 293 grid cells across the European domain with observation-based trend estimates. The ensemble mean overall provided the best representation of trends in the observations. Maps of trends in annual runoff based on the ensemble mean demonstrated a pronounced continental dipole pattern of positive trends in western and northern Europe and negative trends in southern and parts of eastern Europe, which has not previously been demonstrated and discussed in comparable detail. Overall, positive trends in annual streamflow appear to reflect the marked wetting trends of the winter months, whereas negative annual trends result primarily from a widespread decrease in streamflow in spring and summer months, consistent with a decrease in summer low flow in large parts of Europe. High flow appears to have increased in rain-dominated hydrological regimes, whereas an inconsistent or decreasing signal was found in snow-dominated regimes. The different models agreed on the predominant continental-scale pattern of trends, but in some areas disagreed on the magnitude and even the direction of trends, particularly in transition zones between regions with increasing and decreasing runoff trends, in complex terrain with a high spatial variability, and in snow-dominated regimes. Model estimates appeared most reliable in reproducing observed trends in annual runoff, winter runoff, and 7-day high flow. Modelled trends in runoff during the summer months, spring (for snow influenced regions) and autumn, and trends in summer low flow were more variableboth among models and in the spatial patterns of agreement between models and the observations. The use of models to display changes in these hydrological characteristics should therefore be viewed with caution due to higher uncertainty.
Malawi's agro-based economy, based largely on rain fed agriculture production, renders the countr... more Malawi's agro-based economy, based largely on rain fed agriculture production, renders the country highly vulnerable to impacts of climate change and variability. Changes in the seasonal rainfall distribution can be used to predict the impacts of climate change and variability on agricultural productivity. In this study, extreme rainfall indices were analysed at 43 stations and a methodology was proposed for detecting rainfall onset, cessation and length of the growing season at 26 stations in Malawi. These indices were derived from daily rainfall records from 1961 to 2009. Geostatistical techniques and parametric and non-parametric statistics were applied to understand the levels of change in these indices and their distribution functions. The results show a countrywide shift in rainfall onset and cessation, but without significant changes in the length of the growing season; a decrease in total annual rainfall, annual maximum 1-day and 5-day rainfall amount, number of heavy and extreme rainfall days. However, there was an increase in the consecutive number of wet and dry days. Most indices analysed did not show any regionally consistent pattern and were not statistically significant at α = 0.05 level.
Characteristics and drivers of drought in Europe—a summary of the DROUGHT-R&SPI project
CRC Press eBooks, Feb 12, 2015
ABSTRACT A prerequisite to mitigate the wide range of drought impacts is to establish a good unde... more ABSTRACT A prerequisite to mitigate the wide range of drought impacts is to establish a good understanding of the drought generating mechanisms from their initiation as a meteorological drought through to their development as soil moisture and hydrological drought. The DROUGHT-R&SPI project has contributed to increased understanding of: (i) drought as a natural hazard through analysis of historical large-scale droughts in Europe, (ii) drought-controlling mechanisms for various scales, including large-scale climate drivers and local-scale processes, (iii) the potential for drought early warning and forecasting, and (iv) suitable drought indicators. The results provide new insight into key characteristics and drivers of major historical droughts as well as projected future drought. The paper summarises the main outcomes of these studies and identifies further research needs.
Macro-scale hydrological modelling implies a repeated application of a model within an area using... more Macro-scale hydrological modelling implies a repeated application of a model within an area using regional parameters. These parameters are based on climate and landscape characteristics, and they are used to calculate the water balance in ungauged areas. The regional parameters ought to be robust and not too dependent of the catchment and time period used for calibration. The ECOMAG model is applied for the NOPEX-region as a macro-scale hydrological model distributed on a 2×2 km2 grid. Each model element is assigned parameters according to soil and vegetation classes. A Bayesian methodology is followed. An objective function describing the fit between observed and simulated values is used to describe the likelihood of the parameters. Using Baye's theorem these likelihoods are used to update the probability distributions of the parameters using additional data, being it either an additional year of streamflow or an additional streamflow station. Two sampling methods are used, re...
Snow- and glacier melt are important contributors to river discharge in high-elevated areas of th... more Snow- and glacier melt are important contributors to river discharge in high-elevated areas of the Himalayan region. Thus, it is important that the key processes controlling snow and glacier accumulation and melting, are well represented in hydrological models. In this study, the sensitivity of modelled discharge to different snowmelt parameterizations was evaluated. A distributed hydrological model that operated on a 1 × 1 km2 grid at a daily time resolution was applied to a high-elevated mountainous basin, the Upper Beas basin in Indian Himalaya, including several sub-basins with a varying degree of glacier covered areas. The snowmelt was calculated using (i) a temperature-index method, (ii) an enhanced temperature-index method including a shortwave radiation term, and (iii) an energy balance method. All model configurations showed similar performance at daily, seasonal, and annual timescales and a lower performance for the validation period than for the calibration period; a main...
This document is the author's final manuscript version of the journal article, incorporating any ... more This document is the author's final manuscript version of the journal article, incorporating any revisions agreed during the peer review process. There may be differences between this and the publisher's version. You are advised to consult the publisher's version if you wish to cite from this article.
EGU General Assembly Conference Abstracts, May 1, 2010
An understanding of the temporal and spatial characteristics of rainfall is central to water reso... more An understanding of the temporal and spatial characteristics of rainfall is central to water resources planning and management. However, such information is often limited in many developing countries like Malawi. In an effort to bridge the information gap, this study examined the temporal and spatial charecteristics of rainfall in Malawi. Rainfall readings from 42 stations across Malawi from 1960 to 2006 were analysed at monthly, annual and seasonal scales. The Malawian rainfall season lasts from November to April. The data were firstly subjected to quality checks through the cumulative deviations test and the Standard Normal Homogeinity Test (SNHT). Monthly distribution in a typical year, called heterogeneity, was investigated using the Precipitation Concentration Index (PCI). Further, normalized precipitation anomaly series of annual rainfall series (AR) and the PCI (APCI) were used to test for interannual rainfall variability. Spatial variability was characterised by fitting the Spatial Correlation function (SCF). The nonparametric Mann-Kendall statistic was used to investigate the temporal trends of the various rainfall variables. The results showed that 40 of the stations passed both data quality tests. For the two stations that failed, the data were adjusted using nearby stations. Annual and seasonal rainfall were found to be characterised by high spatial variation. The country mean annual rainfall was 1095 mm with mean interannual variability of 26%. The highland areas to the north and southeast of the country exhibited the highest rainfall and lowest interannual variability. Lowest rainfall coupled with high interannual variability was found in the Lower Shire basin, in the southern part of Malawi. This simillarity is the pattern of annual and seasonal rainfall should be expected because all stations had over 90% of their observed annual rainfall in the six month period between November and April. Monthly rainfall was found to be highly variable both temporally and spatially. None of the stations have stable monthly rainfall regimes (mean PCI of less than 10). Stations with the highest mean rainfall were found to have a lower interannual variability. The rainfall stations showed low spatial correlations for annual, monthly as well as seasonal timescales indicating that the data may not be suitable for spatial interpolation. However, some structure (i.e. lower correlation with distance) could be observed when aggregating the data at 50 mile intervals. The annual and seasonal rainfall series were dominated by negative trends. The spatial distribution of the trends can be described as heterogeneous, although most of the stations in the southern region have negative trends. At the monthly timescale, 37 of the stations show a negative trend with four of the stations, all in the south, showing significant negative trends. On the other hand, only 5 stations show positive trends with only one significant trend in the south.
In the current human-modified world, or Anthropocene, the state of water stores and fluxes has be... more In the current human-modified world, or Anthropocene, the state of water stores and fluxes has become dependent on human as well as natural processes. Water deficits (or droughts) are the result of a complex interaction between meteorological anomalies, land surface processes, and human inflows, outflows, and storage changes. Our current inability to adequately analyse and manage drought in many places points to gaps in our understanding and to inadequate data and tools. The Anthropocene requires a new framework for drought definitions and research. Drought definitions need to be revisited to explicitly include human processes driving and modifying soil moisture drought and hydrological drought development. We give recommendations for robust drought definitions to clarify timescales of drought and prevent confusion with related terms such as water scarcity and overexploitation. Additionally, our understanding and analysis of drought need to move from single driver to multiple drivers and from uni-directional to multi-directional. We identify research gaps and propose analysis approaches on (1) drivers, (2) modifiers, (3) impacts, (4) feedbacks, and (5) changing the baseline of drought in the Anthropocene. The most pressing research questions are related to the attribution of drought to its causes, to linking drought impacts to drought characteristics, and to societal adaptation and responses to drought. Example questions include Published by Copernicus Publications on behalf of the European Geosciences Union. 3632 A. F. Van Loon et al.: Drought in a human-modified world (i) What are the dominant drivers of drought in different parts of the world? (ii) How do human modifications of drought enhance or alleviate drought severity? (iii) How do impacts of drought depend on the physical characteristics of drought vs. the vulnerability of people or the environment? (iv) To what extent are physical and human drought processes coupled, and can feedback loops be identified and altered to lessen or mitigate drought? (v) How should we adapt our drought analysis to accommodate changes in the normal situation (i.e. what are considered normal or reference conditions) over time? Answering these questions requires exploration of qualitative and quantitative data as well as mixed modelling approaches. The challenges related to drought research and management in the Anthropocene are not unique to drought, but do require urgent attention. We give recommendations drawn from the fields of flood research, ecology, water management, and water resources studies. The framework presented here provides a holistic view on drought in the Anthropocene, which will help improve management strategies for mitigating the severity and reducing the impacts of droughts in future.
Discharge over the Narayani river catchment of Nepal was simulated using Statkraft's Hydrologic F... more Discharge over the Narayani river catchment of Nepal was simulated using Statkraft's Hydrologic Forecasting Toolbox (Shyft) forced with observations and three global forcing datasets: (i) ERA-Interim (ERA-I), (ii) Water and Global Change (WATCH) Forcing Data ERA-I (WFDEI), and (iii) Coordinated Regional Climate Downscaling Experiment with the contributing institute Rossy Centre, Swedish Meteorological and Hydrological Institute (CORDEX-SMHI). Not only does this provide an opportunity to evaluate discharge variability and uncertainty resulting from different forcing data but also it demonstrates the capability and potential of using these global datasets in data-sparse regions. The fidelity of discharge simulation is the greatest when using observations combined with the WFDEI forcing dataset (hybrid datasets). These results demonstrate the successful application of global forcing datasets for regional catchment-scale modeling in remote regions. The results were also promising to provide insight of the interannual variability in discharge. This study showed that while large biases in precipitation can be reduced by applying a precipitation correction factor (p_corr_factor), the best result is obtained using bias-corrected forcing data as input, i.e. the WFDEI outperformed other forcing datasets. Accordingly, the WFDEI forcing dataset holds great potential for improving our understanding of the hydrology of data-sparse Himalayan regions and providing the potential for prediction. The use of CORDEX-SMHI-and ERA-I-derived data requires further validation and bias correction, particularly over the high mountain regions.
This study is a contribution to the northern hemisphere climate processes land surface experiment... more This study is a contribution to the northern hemisphere climate processes land surface experiment (NOPEX). Its purpose is to investigate the spatial variability of groundwater levels and soil moisture content at different scales in a landscape dominated by boreal forest and till soils, which is characteristic of the Nordic countries. The analysis of data from the NOPEX area are based on a review of previous studies on the spatial distribution of these state variables and their signi®cance for runoff formation. Soil moisture content in the unsaturated zone and depth to the groundwater table show characteristic patterns which are related to the landscape elements (patches) of the drainage basins. Similar behaviour is observed in different parts of the NOPEX region. The variability of average values between areas decreases to a minimum for catchments with size larger than 1 km 2. It can therefore be concluded that the main part of the spatial variability of soil moisture content and depth to the groundwater level in the till soils of the NOPEX area is found within small drainage basins. Based on a physical description of the soil, distribution functions of soil moisture content conditioned on the depth to the groundwater table have been developed, both for the patch scale and the catchment scale.
Space–time modelling of catchment scale drought characteristics
Journal of Hydrology, Sep 1, 2009
... Differences in hydrological stores are the main factor controlling drought propagation, leadi... more ... Differences in hydrological stores are the main factor controlling drought propagation, leading to different lag times between meteorological and hydrological drought across space ([van Lanen and Tallaksen, 2007] and [Peters, 2003]). ...
Your article is protected by copyright and all rights are held exclusively by Springer Science +B... more Your article is protected by copyright and all rights are held exclusively by Springer Science +Business Media Dordrecht. This e-offprint is for personal use only and shall not be selfarchived in electronic repositories. If you wish to self-archive your article, please use the accepted manuscript version for posting on your own website. You may further deposit the accepted manuscript version in any repository, provided it is only made publicly available 12 months after official publication or later and provided acknowledgement is given to the original source of publication and a link is inserted to the published article on Springer's website. The link must be accompanied by the following text: "The final publication is available at link.springer.com".
An understanding of the temporal and spatial characteristics of rainfall is central to water reso... more An understanding of the temporal and spatial characteristics of rainfall is central to water resources planning and management. Such information is often limited in many developing countries like Malawi, an agro-based economy where 90% of the agriculture is rain fed. Most climate models project an overall decline of rainfall for the whole Southern Africa. However, some studies have observed changes in the mean rainfall varying on relatively small spatial scales in the region. The main objective of this study was to investigate spatial and temporal characteristics of annual, seasonal and monthly rainfall in Malawi, a relatively lower spatial scale. In Malawi (Fig. 1), both rainfall and temperature are altitude dependent. Rainfall ranges from 700 mm in the semi-arid low lying parts to 2500 mm in the highlands whereas temperature ranges between 10–40oC countrywide. Two main rain bearing systems dominate the rainfall of Malawi and the Southern Africa region: (1) The Inter tropical Conve...
An overall appraisal of runoff changes at the European scale has been hindered by "white space" o... more An overall appraisal of runoff changes at the European scale has been hindered by "white space" on maps of observed trends due to a paucity of readily-available streamflow data. This study tested whether this white space can be filled using estimates of trends derived from model simulations of European runoff. The simulations stem from an ensemble of eight global hydrological models that were forced with the same climate input for the period 1963-2000. The derived trends were validated for 293 grid cells across the European domain with observation-based trend estimates. The ensemble mean overall provided the best representation of trends in the observations. Maps of trends in annual runoff based on the ensemble mean demonstrated a pronounced continental dipole pattern of positive trends in western and northern Europe and negative trends in southern and parts of eastern Europe, which has not previously been demonstrated and discussed in comparable detail. Overall, positive trends in annual streamflow appear to reflect the marked wetting trends of the winter months, whereas negative annual trends result primarily from a widespread decrease in streamflow in spring and summer months, consistent with a decrease in summer low flow in large parts of Europe. High flow appears to have increased in rain-dominated hydrological regimes, whereas an inconsistent or decreasing signal was found in snow-dominated regimes. The different models agreed on the predominant continental-scale pattern of trends, but in some areas disagreed on the magnitude and even the direction of trends, particularly in transition zones between regions with increasing and decreasing runoff trends, in complex terrain with a high spatial variability, and in snow-dominated regimes. Model estimates appeared most reliable in reproducing observed trends in annual runoff, winter runoff, and 7-day high flow. Modelled trends in runoff during the summer months, spring (for snow influenced regions) and autumn, and trends in summer low flow were more variableboth among models and in the spatial patterns of agreement between models and the observations. The use of models to display changes in these hydrological characteristics should therefore be viewed with caution due to higher uncertainty.
Malawi's agro-based economy, based largely on rain fed agriculture production, renders the countr... more Malawi's agro-based economy, based largely on rain fed agriculture production, renders the country highly vulnerable to impacts of climate change and variability. Changes in the seasonal rainfall distribution can be used to predict the impacts of climate change and variability on agricultural productivity. In this study, extreme rainfall indices were analysed at 43 stations and a methodology was proposed for detecting rainfall onset, cessation and length of the growing season at 26 stations in Malawi. These indices were derived from daily rainfall records from 1961 to 2009. Geostatistical techniques and parametric and non-parametric statistics were applied to understand the levels of change in these indices and their distribution functions. The results show a countrywide shift in rainfall onset and cessation, but without significant changes in the length of the growing season; a decrease in total annual rainfall, annual maximum 1-day and 5-day rainfall amount, number of heavy and extreme rainfall days. However, there was an increase in the consecutive number of wet and dry days. Most indices analysed did not show any regionally consistent pattern and were not statistically significant at α = 0.05 level.
Characteristics and drivers of drought in Europe—a summary of the DROUGHT-R&SPI project
CRC Press eBooks, Feb 12, 2015
ABSTRACT A prerequisite to mitigate the wide range of drought impacts is to establish a good unde... more ABSTRACT A prerequisite to mitigate the wide range of drought impacts is to establish a good understanding of the drought generating mechanisms from their initiation as a meteorological drought through to their development as soil moisture and hydrological drought. The DROUGHT-R&SPI project has contributed to increased understanding of: (i) drought as a natural hazard through analysis of historical large-scale droughts in Europe, (ii) drought-controlling mechanisms for various scales, including large-scale climate drivers and local-scale processes, (iii) the potential for drought early warning and forecasting, and (iv) suitable drought indicators. The results provide new insight into key characteristics and drivers of major historical droughts as well as projected future drought. The paper summarises the main outcomes of these studies and identifies further research needs.
Macro-scale hydrological modelling implies a repeated application of a model within an area using... more Macro-scale hydrological modelling implies a repeated application of a model within an area using regional parameters. These parameters are based on climate and landscape characteristics, and they are used to calculate the water balance in ungauged areas. The regional parameters ought to be robust and not too dependent of the catchment and time period used for calibration. The ECOMAG model is applied for the NOPEX-region as a macro-scale hydrological model distributed on a 2×2 km2 grid. Each model element is assigned parameters according to soil and vegetation classes. A Bayesian methodology is followed. An objective function describing the fit between observed and simulated values is used to describe the likelihood of the parameters. Using Baye's theorem these likelihoods are used to update the probability distributions of the parameters using additional data, being it either an additional year of streamflow or an additional streamflow station. Two sampling methods are used, re...
Snow- and glacier melt are important contributors to river discharge in high-elevated areas of th... more Snow- and glacier melt are important contributors to river discharge in high-elevated areas of the Himalayan region. Thus, it is important that the key processes controlling snow and glacier accumulation and melting, are well represented in hydrological models. In this study, the sensitivity of modelled discharge to different snowmelt parameterizations was evaluated. A distributed hydrological model that operated on a 1 × 1 km2 grid at a daily time resolution was applied to a high-elevated mountainous basin, the Upper Beas basin in Indian Himalaya, including several sub-basins with a varying degree of glacier covered areas. The snowmelt was calculated using (i) a temperature-index method, (ii) an enhanced temperature-index method including a shortwave radiation term, and (iii) an energy balance method. All model configurations showed similar performance at daily, seasonal, and annual timescales and a lower performance for the validation period than for the calibration period; a main...
This document is the author's final manuscript version of the journal article, incorporating any ... more This document is the author's final manuscript version of the journal article, incorporating any revisions agreed during the peer review process. There may be differences between this and the publisher's version. You are advised to consult the publisher's version if you wish to cite from this article.
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