Precipitation characteristics of two complex mountain river basins on the southern slopes of the central Himalayas
This study investigates the daily, monthly, and seasonal characteristics of precipitation and associated forcing processes for their spatial-temporal variations over two geographically distinct river basins (Kaligandaki and Koshi) in Nepal, located on the southern slopes of the central Himalayas. A 34-year (1981–2015) daily precipitation data set of 49 stations between the elevation ranges of 143 to 3870 m asl was used for this investigation. The Gini coefficient, and index, degree and period of precipitation concentrations, and rainfall gradients were derived to examine precipitation distribution characteristics and causes for their variation. A rapid decrease of rainfall with elevation was observed in the Kaligandaki basin throughout the period of record, while this pattern was reversed in the Koshi basin, due to the rain shadow and orographic effects, which is pronounced in the monsoon season. Mountain effects are likely responsible for the distinct differences in daily and monthly precipitation distribution, with irregular patterns observed in the northern region of Kaligandaki basin and southern region in Koshi basin, with uniform patterns in the southern region of Kaligandaki basin and the northern region of Koshi basin. There is also a distinct variation in seasonality, which is higher (concentrated over several months) in the central northern region in Kaligandaki basin and less concentrated in the northern region of Koshi basin. But monthly precipitation characteristics in the western portion of Koshi and the southern region of Kaligandaki basins show high variability and short concentration duration. However, the months when precipitation is concentrated differed between the basins: from late July to August in Kaligandaki and June to September in Koshi basin. This is because the monsoon arrives later in the west than in the eastern part of the country. Variation in number of rainy days is higher in Koshi, but rainfall amount is greatest in Kaligandaki basin due to its proximity to the ocean and the intense effect of the monsoon. In addition to its value for rainfall-induced disaster mitigation strategies and management planning, this study will be useful for hydrological modeling in these areas in the future.
We thank the Department of Hydrology and Meteorology (DHM), Nepal for providing available data. We also thank two anonymous reviewers and the Editor for their constructive comments and suggestions on an earlier version of this manuscript. We also thank Betsy Armstrong for the editing of the manuscript.
This study is financially supported by the National Natural Science Foundation of China (Grants No. 41401082 and 41771088). Suraj Shrestha is financially supported by the CAS-TWAS President’s Fellowship for International PhD Students. Dambaru Ballab Kattel is financially supported by the CAS President’s International Fellowship Initiative (PIFI) for Visiting Scientists (grant no. 2016VEB013).
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