Spatio-temporal patterns of precipitation in arid and semi-arid regions in western India

With the increased availability of global datasets and the consequent proliferation of national and global studies, regional analyses have taken a back seat. However, regional analyses with observed data form the backbone of localised planning to counter climate change and validation of global data. In this context, the spatiotemporal changes in rainfall over different time scales covering the sub-tropical arid and semi-arid regions over the Thar Desert area are studied. The station rainfall data of 137 stations (1973-2008) has been analysed using annual, seasonal, monthly time-series and rainfall indices ('Expert Team on Climate Change Detection and Indices' - ETCCDI). The Mann-Kendall and modified Mann-Kendall tests were used to compute the trends of the rainfall attributes. Application of ETCCDI on station data and at rarely touched Thar Desert area is the novelty of this study. Overall, rainfall shows a decreasing trend. Annual rainfall has decreased by about 16.8% over the study area, with the number of rainy days decreasing by only 2% (1973-2008). An important finding is a potential smoothing of the temporal distribution of rainfall with an overall decrease in monsoon rainfall in 96 (70%) stations and an increase in pre-monsoon rainfall in 104 (76%) stations. This finding is corroborated by a decrease in the continuous dry days in 115 (84%) stations and in the intensity of rainfall in 103 (75%) stations. In most of the cases, it has been found that the trends are non-significant in the western arid part of the Aravalli Range, while they are significant in the eastern part.