An assessment of water requirement of Rabi rice under projected climate change scenario in the Sundarbans, West Bengal

Abstract

The Sundarban region of West Bengal is one of the most fragile and vulnerable zones to the impacts of climate change. Farmers prefer to grow rice during the dry (rabi) season as the yields are higher than in kharif. However, rice cultivation during this season is limited due to the shortage of good quality irrigation water. The surface water resources are limited and with the progress of the dry season, the ground water becomes increasingly saline and unfit for irrigation. Climate change impacts could further complicate the existing problems with serious impact on the agricultural production thereby threatening food and livelihood security of the resource poor farmers. With rising temperatures and changes in rainfall pattern, climate change would affect the water balance, as well as, water requirement of agricultural crops. We therefore assessed the effect of climate change on future water requirement of rabi rice by estimating the crop water requirement with CROPWAT model using the downscaled MarcSim weather data (2016-95) obtained from an ensemble of all 17 General Circulation Models (GCMs) for Representative Concentration Pathways (RCP) 4.5 and 8.5 emission scenarios and compared with the base period (1966-2015). An increasing trend of reference crop evapotranspiration (ET0) was observed for both RCP 4.5 and 8.5 scenario, however the rate was steeper for RCP 8.5 particularly during the period 2076-2095. Compared to the base period (1966-2015), the ET0 increased by 2.30% and 2.21% during 2020s for RCP 4.5 and 8.5, respectively and by 7.15% and 10.76% during 2090s. Similarly, the irrigation requirement of rice during rabi would increase by 6.79% and 6.26% during 2020s for RCP 4.5 and 8.5, respectively and by 9.31% and 13.38% during 2090s. On the other hand, the effective rainfall during the crop growth period would reduce by 22.48% and 30.32% in 2090s for RCPs 4.5 and 8.5, respectively over the base period. The study quantified the impact of future climate change on the ET0 and water requirement of rabi rice which showed and increasing trend under climate change.