Monsoon Climate Change Projection for the Orographic West Coast of India Using High-Resolution Nested Dynamical Downscaling Model

An efficient, reliable very high resolution dynamical downscaling model, a regional climate model (Weather Research and Forecasting-Advanced Research Weather Research and Forecasting) one-way nested into skillful general circulation model (National Center for Atmospheric Research-Community Climate System Model version 4), is configured and implemented for ecologically sensitive, densely populated west coast of India encompassing Western Ghats (WG) having complex, meridionally oriented orography and wide biodiversity. This model with 3km resolution resolves orographic features enabling realistic simulation of physical and dynamical characteristics of present-day Indian summer monsoon (ISM) and extreme events, particularly recent trends in ISM rainfall over WG as observed. Marked skill of this model provides confidence in its future climate projection at regional scale. Future ISM rainfall projection shows significant increase (reduction) over 50.7% (5.8%) of Indian grid points. Significant reduction (10-20% of mean) over WG is due to upper-tropospheric warming effect that stabilizes the atmosphere. Projected changes in extreme events show overall increase in warm days and warm nights over India with maximum increase over South India. Projected changes show widespread increase in wet days over most of India and reduction over WG. Projection of consecutive dry days implies wetter future for most parts of India but strengthened drought conditions for WG. Wind extreme projection shows strengthened (weakened) low (high) winds probability over WG and increase (decrease) in very high (low) winds over central India. This study establishes the importance of (i) employing sufficiently high-resolution model, (ii) using bias-corrected boundary data, and (iii) configuring model for realistic present-day climate over complex topographic coastlines such as the west coast, in order to obtain useful climate change information for adaptation measures.