Relationship between winter precipitation over the western Himalaya and central northeast India summer monsoon rainfall: A long-term perspective

Indian summer monsoon rainfall (ISMR), contributing around 3/4th of the annual precipitation, is the manifestation of land/sea thermal contrast between the Asian land mass and tropical Indian Ocean. Over 125 years ago, Blanford first proposed that the extent of winter snow cover over the Himalayan region, influencing the land/sea thermal contrast, has a significant inverse relationship with ISMR. Although the Himalayas contain the largest volume of ice outside the Polar Regions, a paucity of snow records from this region hampers understanding on the snow/monsoon relationship in long-term perspective. Using tree-ring-based precipitation reconstruction (WPr), from a cold arid region in the western Himalaya, which has a dominant boreal winter snowfall signal, it is demonstrated that the snow anomaly has negative influence on summer monsoon rainfall over central northeast India. The increasing trend in WPr observed over the 20th century could be responsible for decreased land/sea thermal contrast, resulting in the weakening of summer monsoon rainfall. However, this relationship is spatially centered over central northeast India. The WPr in association with other monsoon proxies from southern Tibet and the Himalayan region revealed that the ISMR over a large area, including central northeast India, has weakened in recent centuries. If this trend continues, it will have serious implications for water availability and food security of the country.