Impacts of climate change on the flow of the transboundary Koshi River, with implications for local irrigation

Abstract

This study assesses climate change impacts on the hydrological regime of a river basin and its implications for future irrigation water availability in the Koshi River basin using RCPs 4.5 and 8.5 over short-term (2016-2045), mid-century (2036-2065) and end-of-century (2071-2100) periods. Average flow in the Koshi River is projected to increase. Projections of average minimum monthly river flow suggest that the areas of winter wheat and monsoon paddy rice could be increased. However, the planting period of paddy rice should be delayed by one month (July to August) to capture the expected increased water availability in the river.

Application of SWAT in Hydrological Simulation of Complex Mountainous River Basin (Part II: Climate Change Impact Assessment)

“…This study found that the projected annual flows by all GCMs and for all time windows are greater than the base case. A similar trend has been reported in other studies made in Nepalese rivers basins: for example, Indrawati [31], in Bagmati [62], Kaligandaki [66], Bheri [67], Karnali [29], and Koshi [32,40,59], except [39] in Tamor. Among these results, the trend of increase in ensembled future flows is surprisingly found similar to that of [40].…”

“…A similar trend has been reported in other studies made in Nepalese rivers basins: for example, Indrawati [31], in Bagmati [62], Kaligandaki [66], Bheri [67], Karnali [29], and Koshi [32,40,59], except [39] in Tamor. Among these results, the trend of increase in ensembled future flows is surprisingly found similar to that of [40]. The percentage change in flow due to CC in IF/MF/FF of this study and [40] are, respectively, 21/23/25 and 16/22/28 for RCP 4.5 and 20/29/48 and 18/31/57 for RCP 8.5.…”

“…A relatively new approach of selecting climate models representing four different extreme cases (warm-wet, coldwet, warm-dry, and cold-dry conditions) were applied in the study. Generally, analysis of the impact of CC was limited to annual, monthly, and seasonal flows and based on people's perceptions in most of the previous studies [32,34,[38][39][40]. This study has extended the analyses further to compare with the baseline condition the results of the frequency analysis of the annual one-day-maximum and -minimum flows for three-time windows, i.e., immediate, mid, and far futures.…”

Assessment of climate change impact on hydrology of a transboundary river of Bhutan and India

“…The SWAT model has been used to study the impact of climate change on the hydrology of transboundary rivers. Kaini et al (2020) applied the SWAT model to analyze climate change impacts on the hydrological regime of a river basin and its implications for future irrigation water availability in the Koshi River basin. They found that the average flow in the Koshi River is projected to increase in future.…”

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“…Estimation of changes in seasonality, inter-annual variability, statistical low and high flows, and floods and droughts is required to understand the impact of climate change on humans and freshwater ecosystems [3]. Climate change impact studies for river basins mostly focus on changes of river discharge and aspects of its temporal variability, in particular seasonality [4][5][6][7][8][9]. In Vietnam, research studies on impact of climate change on river flows focusing on changes of flow magnitude and occurence are prominent [10].…”