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The atmospheric branch of the hydrological cycle over the Indus, Ganges and Brahmaputra River basins
Rogert Sorí, Raquel Nieto, Anita Drumond, Sergio M. Vicente-Serrano, Luis Gimeno

Published: 24 July 2017 by Copernicus GmbH in Hydrology and Earth System Sciences Discussions
Copernicus GmbH, 10.5194/hess-2017-378
Abstract: The atmospheric branch of the hydrological cycle over the Indus, Ganges, and Brahmaputra river basins in the South Asian region was investigated. The 3-dimensional model FLEXPART v9.0 was utilized. An important advantage of this model is that it permits the computation of the freshwater budget on air parcels both backward and forward in time trajectories from 0.1 and 1000 hPa in the atmospheric vertical column. The analysis was conducted for the Westerly Precipitation Regime (WPR) (November–April) and the Monsoonal Precipitation Regime (MPR) (May–October) in the period from 1981–2015. The main terrestrial and oceanic climatological moisture sources for the IRB, GRB and BRB and their contribution to precipitation over the basins were identified. For the three basins, the most important moisture sources for precipitation are (i) on the continental regions, the land masses to the west of the basins (in this case called West Asia), the Indian region (IR) and the basin itself, and (ii) from the ocean, the utmost sources are the Indian Ocean (IO) and the Bay of Bengal (BB), and it is remarkable that despite the amount of moisture reaching the IRB and GRB from land sources, the moisture supply from the IO seems to be first associated with the rapid increase/decrease in precipitation over the sources in the MPR. The technique of the composites was used to analyse how the moisture uptake spatially vary from the sources (the budget of evaporation minus precipitation (E − P) was computed in a backward experiment from the basins) but during the preonset and predemise dates of the monsoonal rainfall over each basin; this confirmed that over the last days of the monsoon at the basins, the moisture uptake areas decrease in the IO. The Indian region, the Indian Ocean and the basins itself are the main sources of moisture responsible for negative (positive) anomalies of moisture contribution to the basins during composites of driest (wettest) WPR and MPR.
Keywords: rainfall, model, Indian, MPR, Basins, monsoonal, Moisture Sources
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