On the Present and Future Changes in Climate Extremes over India

Abstract

This work uses state-of-the-art Global and Regional Climate Models to assess present and future changes in climate extremes over India. India has the world’s largest population and many of the people there are extremely vulnerable to future changes in Climate extremes. The fidelity of general circulation models (GCMs) from the Coupled Model Intercomparison Project version 6 (CMIP6), to simulate temperature and precipitation over India. The period of study is split into three parts, historical (1984-2014), near-future (2030-2060) and far-future (2070-2100). The models are found to have varying biases, and the computation of a multi-model mean shows an improvement upon these biases. Future projections make use of the newest Shared Socioeconomic Pathways (SSPs), which generally show an increase in both mean and extreme climate variables. This increase is most extreme under the high emission scenario SSP5-8.5 for both temperature and precipitation. Due to the coarse resolution of GCMs, dynamical downscaling (at 25 km resolution) is applied with the use of the Regional Climate Model version 4.7 (RegCM4.7) from The Abdus Salam International Centre for Theoretical Physics (ICTP). Sensitivity experiments have been carried out to better tune RegCM4.7 to the Indian domain. Orography representation, cumulus convection schemes and land surface schemes are tested, and the best schemes are selected for the purpose of model parameterisation. A better representation of moisture transport, surface fluxes and soil moisture are shown to improve the simulation of temperature and precipitation extremes in the RCM. Envelop orography treatment (i.e. increasing orography from model mean height) by 10%, the use of the Grell over land and Emanuel over ocean cumulus schemes and the Community Land Model land surface scheme are found to give the best results over the Indian domain. The aforementioned RCM is found to improve upon all tested GCMs in the simulation of temperature and precipitation over India. For future simulations, heat waves are found to increase in both frequency and duration when compared to the present climate. The areas most affected by this increase are along the Indo-Gangetic plane, where most of the Indian population resides. Future temperature extremes projected by the RCM are greater than those of the GCMs and heat wave frequency and duration is more severe in RCM simulations. Precipitation intensity is greater in the RCM than the GCM for the PR, however most regions (CNE, HR, NE and NW) are shown to have a decrease in mean precipitation. The areas most impacted by this increase are along the Westcoast of India, where most of the monsoon rainfall occurs. Extreme precipitation is greater during the near future in the RCM for all SSPs and the increase from near to far future is lesser than what is shown by the GCMs. The increases in both climate extremes are found to be worsened when using the high emission scenario SSP5-8.5 and are shown to improve when using the sustainable scenario SSP1-2.6 towards the end of the century. Overall, this study highlights the importance of dynamical downscaling as an important tool for predicting climate extremes over India and understanding the impacts of climate change over this region. These results emphasise the importance of sufficient mitigation strategies to lessen the impact of climate extremes over India and the urgent need to act sooner rather than later.