Multidecadal Variability in Precipitation and Associated Parameters over the Four Homogeneous Indian Regions

Abstract:

Water availability has huge implications for food security, economic growth, health and hygiene, and a decline in total rainfall can have detrimental effects on society. Analyzing four decades of data from 1979-2018 with 1979-1988 as the base decade, we found a gradual decrease in precipitation in Northeast India (NEI) and Northwest India (NWI). Arunachal Pradesh and Meghalaya showed a significant reduction along with depletion in the Gangetic plains. Soil moisture, on the other hand, displays an oscillating pattern between a dry and a moist state in NWI and NEI, and persistent drying in Arunachal Pradesh. The drying in the state of Arunachal Pradesh is due to the combined effect of reduced cloud cover, weaker vertical temperature gradient, increased net surface radiation and surface temperature resulting in soil moisture loss and precipitation depletion. Growing static instability in the lower (~2.5 km) and upper troposphere over the decades, especially in the period 2009-2018 can be attributed to overall atmospheric warming. It implies, given favorable conditions, extreme convective events can precipitate heavily, as seen along the western ghats. A gradual weakening of land surface-precipitation coupling in NWI is observed in each successive decade, which suggests remote effects becoming dominant over local effects during precipitation events. Further, relevant land-atmospheric coupling indices will be presented to quantify their interactions and impact on the changing precipitation patterns over these regions.