Dr. Lal Muthuwatta is a hydrologist by training with specialization in numerical modeling for water resources management. His research and professional background includes over 20 years of experience in the fields of GIS, remote sensing and numerical modeling. He has worked in multiple river basins across Asia and Africa, including Ganges, Salween, multiple river basins in Sri Lanka, and Karkheh in Asia
Changes in future rainfall distribution for the agro-ecological regions of Sri Lanka were analyze... more Changes in future rainfall distribution for the agro-ecological regions of Sri Lanka were analyzed. The baseline period to compare future predictions was taken as 1970 to 2000. Downscaled climate change prediction grids were extracted from the UK Hadley Centre for Climate Prediction and Research Model (HadCM3). These grids were extracted for 2050. In the baseline period 76 stations of 147 showed decreasing trends in annual rainfall and 71 increasing trends. Thirty six of the 76 stations showing a decrease were in the wet zone. In the intermediate zone 17 stations showed increasing trends and in the dry zone 34 stations indicated increasing trends. Mean annual rainfall (MAR) for the baseline period for the whole country was 2094 mm/year while the projected value for 2050 is 2249 mm/year. The increase of MAR over Sri Lanka by 2050 compared to the baseline period is about 7%. The comparison of rainfall between the baseline period and 2050 showed that some areas of the dry zone will rec...
Spatially distributed actual evapotranspiration (ETa) values were estimated based on satellite da... more Spatially distributed actual evapotranspiration (ETa) values were estimated based on satellite data and the Surface Energy Balance System (SEBS) approach for the Karkheh River Basin, Iran. Nineteen cloud free MODIS (Moderate Resolution Imaging Spectroradiometer) images, representing a complete cropping year from November 2002 to October 2003 were acquired and processed. Estimated ETa values were verified using sub-catchment scale water balance analysis. The results revealed that during the study period ETa was estimated at 16680x106m3 and that the water balance closure terms at sub-basin scale ranged from 0.6% to 7.2% of precipitation. This implies that water balance is sufficiently understood. Estimated outflow from the basin was 7.8% of precipitation and indicates that water is a very scarce resource in the Karkheh. Rain fed areas consume about 3720 x106 m3/year and are mainly located in the subcatchments of the upper Karkheh while irrigated areas consume 2680x 106 m3/year and are...
ABSTRACT Two strategies are assessed to increase wheat production in the water-scarce Karkheh Riv... more ABSTRACT Two strategies are assessed to increase wheat production in the water-scarce Karkheh River Basin (KRB) in Iran to meet targets by the year 2025. The strategies proposed are (a) to increase yields in the current irrigated and rainfed wheat areas and (b) to increase the area under rainfed wheat through land conversion. Crop water consumption, based on satellite remote sensing and crop yield data, was used to estimate crop water productivity (CWP) in irrigated and rainfed wheat areas in five sub-basins. CWP for wheat ranges from 0.5–1.63 kg m−3 in irrigated areas to 0.37–0.62 kg m−3 in rainfed areas. Conditions indicating water-stress in wheat areas were assessed by relative evapotranspiration (ETa/ETp) and showed that water-stress only had a minimal effect for about 154,000 ha of irrigated wheat (57%). Land suitability analysis showed that about 71,000 ha of rangelands can be converted into rainfed wheat areas without harming the current water balance in the basin. Statistical analyses showed that more than 70% of the variation in irrigated and rainfed wheat yield at plot level can be explained by water, fertilizer and seed rates. This suggests that wheat production can be increased by improving inputs other than water. Results from this study indicate that it is possible to meet approximately 85% of the wheat production targets in the year 2025 when strategies are combined.
The objective of this study is to present an approach to calibrate a semi-distributed hydrologica... more The objective of this study is to present an approach to calibrate a semi-distributed hydrological model using observed streamflow data and actual evapotranspiration time series estimates based on remote sensing data. First, daily actual evapotranspiration is estimated using available MODIS satellite data, routinely collected meteorological data, and applying the SEBS algorithm. Second, the semi-distributed hydrological model HBV is calibrated and validated using the estimated evapotranspiration and observed discharge. This is done for multiple sub-basins of the Karkheh River basin in Iran. The Nash-Sutcliffe coefficient (NS) is calculated for each sub-basin. Maximum and minimum NS values for the calibration using observed discharge are 0.81 and 0.23, respectively, and using estimated evapotranspiration 0.61 and 0.46, respectively. The comparison of model simulations with multiple observed variables increases the probability of selecting a parameter set that represents the actual hy...
ABSTRACT The SWAT (Soil and Water Assessment Tool) was used to evaluate the impacts of a climate ... more ABSTRACT The SWAT (Soil and Water Assessment Tool) was used to evaluate the impacts of a climate scenario based on IPCC A1B emissions on flows in the Volta River basin in West Africa for 2021–2050 and 2071–2100, using 1983–2012 as the reference period. Overall, the simulation indicates increased variability and a decrease of up to 40% in river flow as a consequence of decreasing rainfall and increasing temperature. In particular, the analysis shows smaller absolute but greater relative changes in the hydrology of the northern (upper) part of the basin, particularly at the end of the century.
The actual state of the water monitoring network in Sri Lanka is limited in many ways. Few rivers... more The actual state of the water monitoring network in Sri Lanka is limited in many ways. Few rivers are actually monitored to international standards, rainguage network is expensive to maintain, weather variable are recorded few time a day in weather stations. A comprehensive water balance monitoring for a river basin needs a dedicated network of weather related sensors, accumulating sufficient temporal information at each location to provide hydrological models with satisfactory spatial and temporal calibration information. This study explores the use of Open Source Hardware (OSHW) combined with Free & Open Source Software (FOSS), including Open Source Geospatial (Osgeo) software, to setup a cheap, customized, entirely replicable set of generic and specialized water monitoring network in a river basin in Sri Lanka.
Changes in future rainfall distribution for the agro-ecological regions of Sri Lanka were analyze... more Changes in future rainfall distribution for the agro-ecological regions of Sri Lanka were analyzed. The baseline period to compare future predictions was taken as 1970 to 2000. Downscaled climate change prediction grids were extracted from the UK Hadley Centre for Climate Prediction and Research Model (HadCM3). These grids were extracted for 2050. In the baseline period 76 stations of 147 showed decreasing trends in annual rainfall and 71 increasing trends. Thirty six of the 76 stations showing a decrease were in the wet zone. In the intermediate zone 17 stations showed increasing trends and in the dry zone 34 stations indicated increasing trends. Mean annual rainfall (MAR) for the baseline period for the whole country was 2094 mm/year while the projected value for 2050 is 2249 mm/year. The increase of MAR over Sri Lanka by 2050 compared to the baseline period is about 7%. The comparison of rainfall between the baseline period and 2050 showed that some areas of the dry zone will rec...
Spatially distributed actual evapotranspiration (ETa) values were estimated based on satellite da... more Spatially distributed actual evapotranspiration (ETa) values were estimated based on satellite data and the Surface Energy Balance System (SEBS) approach for the Karkheh River Basin, Iran. Nineteen cloud free MODIS (Moderate Resolution Imaging Spectroradiometer) images, representing a complete cropping year from November 2002 to October 2003 were acquired and processed. Estimated ETa values were verified using sub-catchment scale water balance analysis. The results revealed that during the study period ETa was estimated at 16680x106m3 and that the water balance closure terms at sub-basin scale ranged from 0.6% to 7.2% of precipitation. This implies that water balance is sufficiently understood. Estimated outflow from the basin was 7.8% of precipitation and indicates that water is a very scarce resource in the Karkheh. Rain fed areas consume about 3720 x106 m3/year and are mainly located in the subcatchments of the upper Karkheh while irrigated areas consume 2680x 106 m3/year and are...
ABSTRACT Two strategies are assessed to increase wheat production in the water-scarce Karkheh Riv... more ABSTRACT Two strategies are assessed to increase wheat production in the water-scarce Karkheh River Basin (KRB) in Iran to meet targets by the year 2025. The strategies proposed are (a) to increase yields in the current irrigated and rainfed wheat areas and (b) to increase the area under rainfed wheat through land conversion. Crop water consumption, based on satellite remote sensing and crop yield data, was used to estimate crop water productivity (CWP) in irrigated and rainfed wheat areas in five sub-basins. CWP for wheat ranges from 0.5–1.63 kg m−3 in irrigated areas to 0.37–0.62 kg m−3 in rainfed areas. Conditions indicating water-stress in wheat areas were assessed by relative evapotranspiration (ETa/ETp) and showed that water-stress only had a minimal effect for about 154,000 ha of irrigated wheat (57%). Land suitability analysis showed that about 71,000 ha of rangelands can be converted into rainfed wheat areas without harming the current water balance in the basin. Statistical analyses showed that more than 70% of the variation in irrigated and rainfed wheat yield at plot level can be explained by water, fertilizer and seed rates. This suggests that wheat production can be increased by improving inputs other than water. Results from this study indicate that it is possible to meet approximately 85% of the wheat production targets in the year 2025 when strategies are combined.
The objective of this study is to present an approach to calibrate a semi-distributed hydrologica... more The objective of this study is to present an approach to calibrate a semi-distributed hydrological model using observed streamflow data and actual evapotranspiration time series estimates based on remote sensing data. First, daily actual evapotranspiration is estimated using available MODIS satellite data, routinely collected meteorological data, and applying the SEBS algorithm. Second, the semi-distributed hydrological model HBV is calibrated and validated using the estimated evapotranspiration and observed discharge. This is done for multiple sub-basins of the Karkheh River basin in Iran. The Nash-Sutcliffe coefficient (NS) is calculated for each sub-basin. Maximum and minimum NS values for the calibration using observed discharge are 0.81 and 0.23, respectively, and using estimated evapotranspiration 0.61 and 0.46, respectively. The comparison of model simulations with multiple observed variables increases the probability of selecting a parameter set that represents the actual hy...
ABSTRACT The SWAT (Soil and Water Assessment Tool) was used to evaluate the impacts of a climate ... more ABSTRACT The SWAT (Soil and Water Assessment Tool) was used to evaluate the impacts of a climate scenario based on IPCC A1B emissions on flows in the Volta River basin in West Africa for 2021–2050 and 2071–2100, using 1983–2012 as the reference period. Overall, the simulation indicates increased variability and a decrease of up to 40% in river flow as a consequence of decreasing rainfall and increasing temperature. In particular, the analysis shows smaller absolute but greater relative changes in the hydrology of the northern (upper) part of the basin, particularly at the end of the century.
The actual state of the water monitoring network in Sri Lanka is limited in many ways. Few rivers... more The actual state of the water monitoring network in Sri Lanka is limited in many ways. Few rivers are actually monitored to international standards, rainguage network is expensive to maintain, weather variable are recorded few time a day in weather stations. A comprehensive water balance monitoring for a river basin needs a dedicated network of weather related sensors, accumulating sufficient temporal information at each location to provide hydrological models with satisfactory spatial and temporal calibration information. This study explores the use of Open Source Hardware (OSHW) combined with Free & Open Source Software (FOSS), including Open Source Geospatial (Osgeo) software, to setup a cheap, customized, entirely replicable set of generic and specialized water monitoring network in a river basin in Sri Lanka.
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