Climate variability impact on water resources in the command area of a river diversion scheme

Abstract

Climate change is the major cause that affects water availability mainly due to variability in rainfall and temperature. The rising population and increasing food demands are imposing a further pressure on available water resources. Hence the efficient management of available water resource is of great concern. Irrigation is the largest sector that accounts for water use. In this situation a study was conducted in the command area of Left Bank Canal of Chalakudy River Diversion Scheme to assess the impact of climate variability on the water availability for the cropping systems and domestic demand during the irrigation period from December to May. The variability and trend in the rainfall was studied for the basin for a period from 1987 to 2016 and it is seen that the annual rainfall shows a declining trend. An investigation was done for finding out the cropping pattern of the canal commands. The crop water demand worked out using CROPWAT was used to estimate irrigation water demand. The domestic water demand calculated for the basin along with the irrigation water requirement constituted the net water demand. The total weekly water requirement was computed for all the branch canals for the irrigation period. The groundwater level analysis was done for wells along branch canals. Water recharge was observed in almost all the observation wells during supply periods. But no recharge was observed in wells in tail reaches during certain supply periods due to insufficient supply of water to tail ends. The weekly water supply for the branch canals were compared with the water demand. Most branches show a water deficit while a few exhibits water excess. Water deficit was observed mostly in longer and farther branches. The existing supply system was noted to be inefficient and works without considering proper branch wise water demand. The discharge from the main shutter was also obtained and was found to be almost about five times of the demand. Seepage losses, illegal withdrawal of canal water, and improper management are observed to be the reasons behind the insufficient water supply. Proper management of canals and supply based on demand has to be followed for efficient water management. A computer based model was developed for the calculation of weekly water demand based on crop and weather data. A comparison of supply with the demand can also be done in the model which indicates the efficiency of supply system on a weekly basis. Proper planning can be done for efficient water management through the canal system, under the given conditions using the model.