Assessing climate change impacts in the Cauvery Basin using evapotranspiration projections and its implications on water management

This study analyses the variability in climate change projections under different Shared Socio-economic Pathway (SSP) scenarios to understand the trends of crop water requirements using the reference evapotranspiration (ET_o) as a baseline indicator in the Cauvery Basin, India. A novel approach to ensemble different Global Circulation Models (GCMs) using deep learning techniques was developed to obtain the best representative climate projections. The current progression of climate aligns with the SSP5 scenario, indicating a potential climate distress in the future. Ensembled climate projections were used to estimate the daily ET_o using Hargreaves radiation method. Comprehensive insights into the trends of ETo under different techniques indicate a downward trend over 80% of the basin. The rate of change in trend is severe towards the mountainous western parts of the basin compared to the urbanized eastern region, which experiences a much gentler rate of change. The critical change in the increasing trend over the eastern region coincides with the north-east monsoon, while the decreasing trend occurring predominantly in the western region coincides with the south-west monsoon. SSP3-7.0 scenario was noted to produce the highest impact in the increase of average ET_o to about 6.45% the current trend, while SSP2-4.5 scenario resulted in a rise of only 0.79%. It was found that ETo is highly correlated with the difference between maximum and minimum temperatures scoring an R value around 0.97 in all scenarios. While the highest temperatures (42.17 °C vs 41.03 °C) were observed in SSP5 scenario, the higher average temperature (36.49 °C vs 33.27 °C) in SSP3 scenario has a much higher impact on the ETo across the basin.