Rainfall pattern over the North-West Himalayan region: historical time period vs. future warming scenarios

Abstract

Events like melting glaciers, rising sea level, and changing weather patterns are being observed across the globe due to widely reported global warming. The monsoon season rainfall in the North-Western Himalayan region (NWH) becomes more uncertain as there is considerable variation between the duration of the monsoon season and the amount of rainfall during the season. The NWH region receives substantial amount of rainfall and witness various disasters during the monsoon season. In this context, the present study deals with the analysis of the rainfall patterns under various future warming scenarios (2076–2100), namely representative concentration pathway scenario 4.5 (RCP 4.5) and RCP 8.5 (RCP 8.5) with respect to the reference historical time period (1976–2000) during the principal monsoon season (i.e. 1st June to 30th September) of two Indian states (Uttarakhand and Himachal Pradesh) of the NWH region. To serve this purpose, six attributes are defined as follows; start date of the rainy season (SRS), date of the 50% of the seasonal total rainfall (HRS), end date of the rainy season (ERS), length of the rainy season (LRS), 1 day maximum intensity (MRS) and the day corresponding to the maximum rainfall intensity (MDRS). These attributes are estimated for both historical time period and various future warming scenarios based on the archives of five coupled climate models which participated in the Climate Model Inter-comparison Project Phase 5 (CMIP5). Considering huge inter-model variations amongst the CMIP5 models, results are presented here based on the multi-model mean (MME). Characteristics of various attributes of rainfall during the historical time period are compared with that of the two future warming scenarios viz.; RCP 4.5 and RCP 8.5 by means of statistical techniques. There is a possibility of early SRS, delayed ERS and extended LRS along with intense MRS under different future warming scenarios over Himachal Pradesh (HP) as compared with the historical time period; however, results are significant only for 1 day maximum rainfall under RCP 8.5. Similarly, over the Uttarakhand (UK) region, changes in the rainfall pattern are noted under two future warming scenarios viz.; RCP 4.5 and RCP 8.5 as compared with the historical time period; nonetheless, significant changes are noted in MRS and MDRS only under RCP 8.5. It is anticipated that both of the NWH states of HP and UK would experience enhanced MRS under the warmest future warming scenario (i.e. RCP 8.5). Based on the present analysis, intense rainfall events are expected which could act as an initiator for various meteorological hazards over the NWH region in future.