Deciphering the relevance of background changes to extreme rainfall events in southern India

Abstract

In this thesis, I investigated the potential roles of background changes in the tropical Indo- newlinePacific SSTs and land-use land-cover (LULC) on the intensity and frequency of extreme newlinerainfall events (EREs) in southern India. Toward this end, I conducted several sensitivity newlineexperiments using the Weather Research and Forecasting (WRF) regional climate model with newlinevarious combinations of observed and climatological SST, and those to evaluate the importance newlineof lower boundary LULC conditions. I also explore the importance of assimilating the satellitebased newlineproduct of Global Positioning System (GPS) Radio Occultation (RO) dataset in newlineimproving the prediction skills of the EREs. newlineAt the outset, I investigated the influence of the important individual tropical ocean climate newlinedrivers, specifically, the El Niño Southern Oscillation (ENSO), ENSO Modoki, Indian Ocean newlineDipole (IOD) and the Atlantic Zonal Mode (AZM), on the EREs over India during the ISM newlinefrom 1980 to 2019. My results suggest that the statistics related to summer monsoon, such as, newlinethe mean rainfall, rainy days, normal, moderate, and heavy rainfall events, and 75, 99, and 95 newlinepercentile of rainfall magnitudes increased by 10%-30% mainly over northwestern regions of newlineIndia. Interestingly, the EREs increased about 40% over Gujarat, some places in central India, newlineand Odisha during the 2000-2019 period compared to 1980-1999 period. In addition, the IOD newlineand AZM indices also show significantly increasing trends since the year 2000. My composite newlineand partial correlation analyses show that, since then, the strengthening of positive IODs is newlinesignificantly increasing the seasonal mean rainfall, heavy rainfall events, 95 and 99 percentile newlinerainfall magnitudes over northwestern, and the ERE frequency over Gujarat, central India, and newlineOdisha regions of India. The El Niño, El Niño Modoki, and positive AZM events do not show newlineany significant association of these changing characteristics in these regions. An increasing newlineSST in the equatorial Indian Ocean maximized in its west, and consequent s