•A procedure is tested to complete energy balance based daily ETa series by MODIS data.•The HVB model is calibrated on 2 water balance terms; ETa and stream flow (Q).•HBV calibration on Q shows poor ...ETa results for inter-rainfall and recession periods.•Multi-variable (MV) vs. single variable calibration showed best HBV performance.•Large volume differences in Q and ETa do not essentially effect MV calibration.
In this study, streamflow (Qs) and satellite-based actual evapotranspiration (ETa) are used in a multi-variable calibration framework to reproduce the catchment water balance. The application is for the HBV rainfall–runoff model at daily time-step for the Karkheh River Basin (51,000km2) in Iran. Monte Carlo Simulation serves to estimate parameter values and to assess uncertainty for three calibration cases. In case one streamflow is used as the calibration target. In case two satellite-based ETa is used as calibration target. For both cases model performance is evaluated for the second variable that closes the water balance. In case three a preference-based multi-variable objective function is applied which is weighted for Qs and satellite-based ETa. For cloudy days a procedure is developed to complete the daily time series of satellite-based ETa that cover 4years.
Results on multi-variable calibration indicated satisfying results for both water balance terms. Results are compared against field observations and results of single-variable calibration. For cases one and two the second variable only is poorly simulated and resulted in poor reproduction of the water balance. The most important contribution of this work is that the catchment water balance is best reproduced when both Qs and satellite-based ETa serve as calibration target.
Climate change causes shifts in areas suitable for cultivating a wide range of crops. Sugarcane is a perennial crop currently grown in the intermediate and dry zones of Sri Lanka. However, there may ...be shifts in the potential areas for sugarcane cultivation due to climate change. This study thus attempted to analyze the suitability of rain-fed areas for cultivating sugarcane in Sri Lanka under the current and future projected climate. Ecocrop model was used to predict the climatically suitable areas for sugarcane, based on the present and future climate scenarios. Monthly minimum and maximum temperature, monthly mean rainfall, and crop data were used as inputs to the model. Climate data of the baseline period (1971–2000) were evaluated against the projected climate data in 2030 and 2050 under a Representative Concentration Pathway (RCP) of 4.5 and 8.5 emission scenarios of six Global Climate Models Projected changes revealed to increase the area of intermediate zone of the country by 128, 8, 135, and 170% at RCP 4.5, 2030; RCP 8.5, 2030; RCP4.5, 2050, and RCP 8.5, 2050, respectively, compared to baseline status. Areas for optimum temperature range for sugarcane have expanded in future time periods in the country under two scenarios. The excellent suitable areas for cane growth are projected to increase in 2030 by 56 and 47%, under RCP 4.5 and RCP 8.5, respectively. Considering the aggregated effect of temperature and rainfall, areas for sugarcane cultivation in Sri Lanka tend to increase with climate change.
•Two strategies are proposed and assessed to increase wheat production in water scarce KRB.•By converting land use, rainfed wheat areas could be increased by an additional 71,000ha in KRB.•Yield in ...154,000ha of irrigated wheat can be increased by using only fertilizer and seeds.•Available water resources in KRB are sufficient to produce an additional 425×106kg of wheat.
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 0.5–1.63kgm−3 in irrigated areas to 0.37–0.62kgm−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 154,000ha of irrigated wheat (57%). Land suitability analysis showed that about 71,000ha 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.
This study was conducted to assess water availability and consumption in the Karkheh River Basin in Iran using secondary data and freely available satellite data. Precipitation was estimated using ...geo-statistical techniques while a Surface Energy Balance approach was selected for evapotranspiration estimation. The spatial distribution of actual evapotranspiration (ETa) for the Karkheh Basin has been estimated by use of 19 cloud free Moderate Resolution Imaging Spectroradiometer (MODIS) images, which cover a complete cropping year from November 2002 to October 2003. ETa estimates were compared to potential crop evapotranspiration (ETp) estimates for two predominantly irrigated wheat areas in Upper and Lower Karkheh. Differences were found to be 12.5% and 11.7% respectively. Results of the ETa and precipitation estimates reveal that for the study period, the Karkheh Basin received 18,507 × 10⁶m³ as precipitation while ETa is estimated at 16,680 × 10⁶m³. Estimated outflow from the basin for the study period only is 7.8% of the precipitation and indicates that water is a very scarce resource in the Karkheh basin. The basin has been divided in sub-basins to allow for more detailed analysis and results indicate that water balance closure at sub-basin scale ranges from 7.2% to 0.6% of the precipitation. This suggests that the water balance is sufficiently understood for policy and decision making.
Selected rainfall characteristics derived by analyzing observed rainfall data in two Sri Lankan river basins (Malwathu Oya and Kalu Ganga) were compared with the perceptions of farmers. The rainfall ...characteristics used for this analysis are trends, onset and cessation dates, length of the growing period, number of rainy days, and length of the dry spell. Farmers' perceptions of changes in those characteristics were collected through household surveys. The majority of farmers in both river basins failed to recognize the long-term upward trend in annual rainfall. They also failed to describe the adaptation measures they were currently practising.
In an 18-month study of malaria in a population of 1,875 residents in 423 houses in an endemic area in southern Sri Lanka, the risk of malaria was found to be 2.5-fold higher in residents of poorly ...constructed houses than in those living in houses of good construction type. In residents of poorly constructed houses but not in others, the risk was even greater when the house was located near a source of water that could act as a potential breeding place for malaria vector mosquitoes (P = 0.0001). Based on previous findings that confirmed that house construction type was itself a risk determinant, and not merely a marker of other behavioral factors, we have estimated the potential impact of two feasible interventions to reduce the risk of malaria: 1) the imposition of a buffer zone of 200 meters around bodies of water from which houses of poor construction were excluded, which was estimated to lead to a 21% reduction of the malaria incidence in the overall population and a 43% reduction in the relocated community; and 2) the conversion of houses of poor construction type located in the buffer zone to those of a good construction type, which was estimated to lead to a 36% reduction in the incidence rates in the whole population and a 76% reduction in the residents of houses whose construction type was improved. Taking into consideration the cost to the Government of malaria prevention, we estimated the worth of a Government's investment in improving house construction type. The investment in housing was estimated to be offset in 7.2 years by savings to the Government on malaria costs alone, and beyond this period, to bring a return on the Government's investment by way of savings to the malaria control program.
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