Abstract:
Pakistan has a rich and vast natural resource base covering various ecological and climatic zones that strengthens the agriculture in Pakistan. The relatively good yields in agricultural products are related to timely availability of the required quantity of water besides other inputs. In the context of agriculture, water and yield, the subject of consumptive use of water or evapotranspiration (ET) is becoming increasingly important, particularly in arid and semi-arid areas of Pakistan. This research study aims to determine the effectiveness and utility of remote sensing in determining the water consumption by the crops in the Soan River basin where the agriculture is mainly dependent upon rainfall. The main objective of this research is to assess the actual evapotranspiration of Rabi cropped area by satellite image, applying Surface Energy Balance Algorithm for Land (SEBAL) and comparison of calculated values with CROPWAT model. Satellite Remote Sensing allows instantaneous analyses of the situation as well as temporal to give an immediate response towards assessment and monitoring of evapotranspiration in a short time period as compared to field techniques. The calculated values of ET for the cultivated area of Rabi crops and forest in the Soan basin are 4.20 mm/day and 5.30 mm/day respectively. Similarly, the average calculated value of evapotranspiration through CROPWAT model for cultivated area and forest are 4.49-4.87 mm/day and 5.10 mm/day respectively. The normalized values of ET calculated through SEBAL are compared with the average values of CROPWAT Model. The resultant pattern of evapotranspiration shows the range of 4.71-4.82 mm/day within the vicinity of the meteorological observatory of Islamabad, hence the average normalized value of ET calculated
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through SEBAL is in the close approximation of average value calculated through CROPWAT model. This value varies from north to south of the study area. The value for the forest evapotranspiration shows 5 percent variation which may be upto 15 percent in the cultivated region. One of the strong reasons for this variation is the maturity level of crop growth. The results show that the remote sensing technique coupled with CROPWAT model shows great potential to calculate the water consumption spatially with the help of SEBAL in rainfed portion of the study area (Soan River basin, Pakistan).
