Hydrologic changes in Indian sub-continental river basins (1901-2012)

Abstract

Long-term (1901-2012) changes in hydroclimatic variables in the 18 Indian sub-continental basins were examined with hydrology simulated using the Variable Infiltration Capacity (VIC) model. Change point analysis using the Sequential Mann-Kendall test showed two distinct periods (1901-1947 and 1948-2012) for the domain averaged monsoon season (June to September) precipitation. Hydrologic changes for the entire water budget were estimated for both periods. In the pre-1948 period, a majority of the river basins experienced increased monsoon season precipitation, evapotranspiration, and surface water availability (as defined by total runoff). Alternatively, in the post-1948 period, monsoon season precipitation declined in 11 of the 18 basins, with statistically significant trends in one (the Ganges basin), and most (15) basins experienced significant warming trends. Additionally, in the post-1948 period the mean monsoon season evapotranspiration (ET) and surface water availability declined in eight (with significant declines in four) basins. Our results indicate that changes in ET and surface water availability in the pre and post 1948 periods were largely driven by the changes in the monsoon season precipitation rather than air temperature, despite prominent warming after 1975. Coupled modes of variability of sea surface temperature (SST) and surface water availability indicated El Nino Southern Oscillation (ENSO) as the leading mode. The second mode was identified as the trend mode for surface water availability in the sub-continental river basins, which was largely driven by SST anomalies in the Indian and Atlantic Ocean regions. This indicates that surface water availability in India’s sub-continental basins may be affected in the future in response to changes in large scale climate variability.