COMPARISON OF CMIPS AND CMIP6 TO UNDERSTAND THE CHANGES IN HISTORICAL AND FUTURE PROJECTIONS OF PRECIPITATION AND TEMPERATURE OVER INDIA

Abstract

Climate change has led to an increase in the frequency of extreme climatic events in different parts of the world. The intensity and spatial extent of these extremes has also considerably increased in the recent years. To understand these changes in the climate, General Circulation Models (GCMs) are widely used, which provide projections of the future climate under different scenarios of greenhouse gasses (GHG) concentration, land use and land cover, and socioeconomic factors. To monitor the progress in climate modelling and future projections, Coupled Model Intercomparison Project (CMIP) framework was designed by IPCC. CMIP has been updated time to time to incorporate different drivers of climate change in the scenarios. The aim of this thesis is to evaluate and compare the climate projections under recent version of CMIP (i.e., CMIP6) with its earlier phase (CMIP5) over India. Two GCM ensembles, comprising of 20 GCMs for CMIP5 and 13 GCMs for CMIP6, were compared for precipitation, temperature and 17 climate extreme indices (CEIs). Four Representative Concentration Pathways (RCPs), namely, RCP2.6, RCP4.5, RCP6.0, RCP8.5, for CMIP5 and four Shared Socioeconomic Pathways (SSPs) namely SSP126, SSP245, SSP370, SSP585 for CMIP6, were considered in this study. The future projections were divided into three intervals: near future (F1), mid future (F2) and far future (F3). The spatial pattern of precipitation and temperature under both CMIP5 and CMIP6 GCMs were found consistent with the observed data. The quantitative change assessment shows that CMIP6 GCMs are projecting higher values for precipitation and temperature compared to CMIP5 GCMs. The percentage change in precipitation was found as high as 62.45% for F3 under SSP585 compared to 38.8% under RCP8.5 in some regions. The trend in country-average daily maximum temperature (Tmax) and daily minimum temperature (Tmin) was higher under CMIP6 than CMIP5. Similarly, higher values of climate extreme indices are projected under CMIP6 than CMIP5 in some parts of the country. This study shows that there are some similarities as well as differences in CMIP5 and CMIP6 projections.