Performance evaluation of CORDEX-South Asia simulations and future projections of northeast monsoon rainfall over south peninsular India

The northeast monsoon (October-December; NEM) rainfall is a very important entity to about 250 million people residing in the South Peninsular India (SPI) region as it is their principle rainy season and contributes mostly to their annual rainfall. The aim of the study is to obtain the future projections of NEM rainfall over this region representing three different greenhouse gas emission scenarios (i.e., RCP 2.6, RCP 4.5 and RCP 8.5) for two future time slices, i.e., near (2020-2049) and far future (2070-2099) estimated from a set of high-resolution regional climate simulations performed under CORDEX-SA experiments. To achieve that, first, an assessment of ten CORDEX-SA regional climate model (RCM) simulations is done for NEM rainfall over SPI for present climate (1976-2005) against India Meteorological Department high resolution (0.25o x 0.25o) gridded rainfall analysis dataset. Then, the change in NEM rainfall over SPI in the near and far future is computed after applying standardized reconstruction technique to adjust the bias present in the models. The results suggest that most of the CORDEX-SA experiments are able to simulate the spatial distribution of NEM seasonal rainfall and its variability over SPI but there is an inability in capturing realistic magnitudes and the errors are more over the east and west coast where most of the rainfall occurs. The experiment with RCA4 driven by EC-EARTH global model and REMO2009 driven by MPI-ESM has a fairly lesser bias than the other models, whereas the bias is more in LMDZ-IITM-RegCM4. The experiments by CCAM models have very similar characteristics in representing the rainfall pattern. The standardized reconstruction bias correction technique was found to significantly improve the performance of the climate models in representing the climatological mean and inter-annual variability of (IAV) of NEM rainfall over SPI, but in case of categorical rainfall years, improvement is seen only in the normal rainfall years. In the future, for RCP 2.6, there is a rise in NEM rainfall in the first half of the twenty-first century, which is projected to decline after that; however, in the other two scenarios, the rainfall is projected to increase. It is also found that there may be lesser excess rainfall years and more deficit rainfall years in the RCP 4.5 and 8.5 scenarios in the near future, and no deficit rainfall years are projected in the far future in both these scenarios based on the present climate. It is also noticed that the variability in the NEM rainfall over this region may remarkably increase in all the three future scenarios, which will highly impact various water resources management sectors. Thus, this study is very useful in determining the effects on various sectors due to the variability in NEM rainfall over this region and for adapting to climate change using advanced technologies for a sustainable future.