Precipitation Trends in the Ganges-Brahmaputra-Meghna River Basin, South Asia: Inconsistency in Satellite-Based Products

Abstract

The Ganges-Brahmaputra-Meghna (GBM) river basin is the world’s third largest. Literature show that changes in precipitation have a significant impact on climate, agriculture, and the environment in the GBM. Two satellite-based precipitation products, Precipitation Estimation from Remotely Sensed Information using Artificial Neural Networks-Climate Data Record (PERSIANN-CDR) and Multi-Source Weighted-Ensemble Precipitation (MSWEP), were used to analyze and compare precipitation trends over the GBM as a whole and within 34 pre-defined hydrological sub-basins separately for the period 1983–2019. A non-parametric Modified Mann-Kendall test was applied to determine significant trends in monsoon (June–September) and pre-monsoon (March–May) precipitation. The results show an inconsistency between the two precipitation products. Namely, the MSWEP pre-monsoon precipitation trend has significantly increased (Z-value = 2.236, p = 0.025), and the PERSIANN-CDR monsoon precipitation trend has significantly decreased (Z-value = −33.071, p < 0.000). However, both products strongly indicate that precipitation has recently declined in the pre-monsoon and monsoon seasons in the eastern and southern regions of the GBM river basin, agreeing with several previous studies. Further work is needed to identify the reasons behind inconsistent decreasing and increasing precipitation trends in the GBM river basin.

The extraordinary Namche Barwa sediment factory in the Eastern Himalayan Syntaxis

“…200,000 km 2 of the Tibetan Plateau. The annual precipitation remained constant as 700–900 mm in the Yarlung and Parlung gorges from 1981 to 2016 (Figure 8a), much lower than along the Himalayan topographic front in India (1500–4000 mm; Khatiwada & Curtis, 2021; Wang et al, 2020b), and channel steepness decreases from k sn > 800 in the Yarlung and Parlung gorges to k sn < 400 in the Siang River downstream (Figure 7). The lack of correlation between sediment yield from different catchments and average precipitation in the NBS ( R 2 = 0.26, p > .05) (Figure 9c) indicates that the spatial distribution of precipitation is decoupled from sediment yield and erosion rates.…”

“…Khatiwada & Curtis, 2021; Wang et al, 2020b), and Factors controlling focused erosion in the Eastern Himalaya Syntaxis. (a) Areal distribution of precipitation, earthquakes with magnitude >4.3 (1981-2011 data from United States Geological Survey Earthquake Hazards Program https://earth quake.usgs.…”

Increased aerosol scattering drives recent monsoon rainfall decrease over northern India

“…Observations of precipitation from multi-sources, including ground-based rain gauge and satellites, reveal a drying trend in the monsoon season over northern India, especially the Gangetic Basin (GP, Fig. S1), in the past few decades [7][8][9][10] , which has caused adverse impact on the social and economic activities in this most populated region all over the globe. At the same time, the intensive human activities in northern India released large amounts of pollutants to the atmosphere, causing an increase in the observed aerosol optical depth (AOD) over the past few decades 11,12 .…”