Trends and persistence in precipitation in the Ganges, Brahmaputra and Meghna river basins

The Ganges, Brahmaputra and Meghna (GBM) river basins occupy about 1.75 x 10(6) km(2) of the Himalayan region. More than half a billion people in Nepal, India, Bhutan and Bangladesh are directly or indirectly dependent on the water resources of the GEM rivers. These river basins are characterized by diversified climatic patterns. Analyses of trends and persistence in precipitation over these river basins are necessary for sound water resources planning. Time series of annual precipitation for each of the 16 meteorological subdivisions covering the three river basins were examined for trends using the Mann-Kendall rank statistic, Student's t-test and regression analysis, and for persistence using first order autocorrelation analysis. Results indicate that precipitation in the Ganges basin is by-and-large stable. Precipitation in one subdivision in the Brahmaputra basin shows a decreasing trend and another shows an increasing trend. One of the three subdivisions in the Meghna basin shows a decreasing trend while another shows an increasing trend. Markovian persistence is not present in the precipitation series in the Ganges basin but it is present in two common subdivisions in the Brahmaputra and Meghna basins.