CLIMATE CHANGE IMPACT ASSESSMENT ON THE IRRIGATION DEMAND IN A PENINSULAR RIVER BASIN OF INDIA

Abstract

Spatial distribution of weather parameters like rainfall, temperature, evapotranspiration, relative humidity, solar radiation etc are changing with time with the effect of climate change. These weather parameters are crucial in hydro-meteorological studies. The study area (Hemavthy project-Goruru-Dam) falls in semi-arid type of climate with large-scale agricultural activities. The agricultural command area within the study area is 265074 ha with the provision of irrigation through left bank canal(LBC) and right bank canal (RBC). The existing cropping pattern has been considerably deviated from the designed cropping pattern due to several reasons. Therefore, the irrigation supply from the existing reservoir for the existing cropping pattern in canal command area requires alterations to meet the present irrigation demand as well as for future in view of the climate change effect. Further, it is also necessary to investigate the available runoff from the major streams to meet the demand requirement. This is achieved through hydrological modelling using SWAT in the present study. Before investigation the supply and demand for the command area, an investigation has been made on the spatial variability and trends of key climate variables viz. rainfall, temperature maximum, and temperature minimum using Mann-Kendall and Sen’s slope estimator for the period during 1985-2014. The spatial distribution of rainfall in annual and pre-monsoon seasons shows upward trend, in monsoon season the area near to reservoir shows downward trend which will affect the overall inflow in to the reservoir. The lower catchment tail end of Tumkuru branch canal is showing an upward trend. In post-monsoon season the rainfall shows downward trend in entire study area, in winter tail end of Tumakuru branch canal shows downward trend. This will have a direct bearing on the moisture availability during Rabi season in study area. Annual maximum temperature, during monsoon, post-monsoon and winter seasons shown upward trend excepting during pre-monsoon herein a downward trend was witnessed in the entire study area. Upward trend in temperature will trigger more water demand in the study area. To meet the supply and demand of water in command area the combination of water use methods is necessary and study is conducted by taking monitoring well data. The results show the ground water itself is not able to meet the entire crop water demand hence the combination use of both conjunctive use helps in best use of available water resources is possible. An attempt has also been made to a assess the future demand by using RCM, MIROC-5 climate model with scenario RCP4.5 and RCP 8.5 in CROPWAT 8.0 model. For advance planning of agricultural or water resources management the future assessment of runoff is done. The runoff assessment was carried out by using SWAT hydrological model. The simulated runoff was validated with the observed data. The model performance is evaluated with quantitative statistics methods like R2, NSE, PBIAS and RSR indicating a good agreement. The study is xi more ever helpful in designing agricultural optimization model for basin with sustainable water resource management.