Soil Moisture Droughts under the Retrospective and Projected Climate in India*.

Changes in precipitation, air temperature, and model-simulated soil moisture were examined for the observed (1950-2008) and projected (2010-99) climate for the sowing period of Kharif and Rabi [KHARIF_SOW (May-July) and RABI_SOW (October-December)] and the entire Kharif and Rabi [KHARIF (May-October) and RABI (October-April)] crop-growing periods in India. During the KHARIF_SOW and KHARIF periods, precipitation declined significantly in the Gangetic Plain, which in turn resulted in declines in soil moisture. Statistically significant warming trends were noticed as all-India-averaged air temperature increased by 0.40°, 0.90°, and 0.70°C in the KHARIF, RABI_SOW, and RABI periods, respectively, during 1950-2008. Frequency and areal extent of soil moisture-based droughts increased substantially during the latter half (1980-2008) of the observed period. Under the projected climate (2010-99), precipitation, air temperature, and soil moisture are projected to increase in all four crop-growing seasons. In the projected climate, all-India ensemble mean precipitation, air temperature, and soil moisture are projected to increase up to 39% (RABI_SOW period), 2.3°C, and 5.3%, respectively, in the crop-growing periods. While projected changes in air temperature are robust across India, robust increases in precipitation and soil moisture are projected to occur in the end-term (2070-99) climate. Frequency and areal extents of soil moisture-based severe, extreme, and exceptional droughts are projected to increase in the near- (2010-39) and midterm (2040-69) climate in the majority of crop-growing seasons in India. However, frequency and areal extent of droughts during the crop-growing period are projected to decline in the end-term climate in the entire crop-growing period because of projected increases in the monsoon season precipitation. [ABSTRACT FROM AUTHOR]