Future runoff trends in the mang river basin of China: Implications of carbon emission paths.

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In recent years, the rapid development of the global economy has led to an increasing impact of the ongoing climate warming phenomenon on the hydrological cycle. In this context, the runoff changes affected by human activities are more severe. This study classifies climate scenarios based on carbon emission levels into "low-carbon" (SSP1-2.6, SSP2-4.5) and "high-carbon" (SSP3-7.0, SSP5-8.5) dual carbon development paths, and analyzes the evolution characteristics of runoff in the Mang River Basin in the near future (2021-2060) and far future (2061-2100) through driving the SWAT model. The main conclusions are as follows: (1) The suitability of the SWAT model in the Mang River Basin was confirmed with a high accuracy (R2>0.65, NSE > 0.8), and the parameters ESCO and SOL_AWC were found to have a high sensitivity to runoff. (2) Increased precipitation fluctuation and continuous temperature rise will be the climate change trend in the basin under the dual carbon pathway. It is estimated that by the end of the 21st century, the overall highest temperature will increase by 1.37-5.02°C, with temperature increases of 0.53-0.63°C/10a and 0.17-0.38°C/10a under the "high carbon" and "low carbon" pathways, respectively. Furthermore, the far future precipitation levels are expected to be higher than near future levels across various climate scenarios, with this trend being especially significant under the "low-carbon" pathway. (3) With the influence of climate change, there is a larger increase in runoff volume under the "high-carbon" pathway, with the growth rate of SSP5-8.5 being the fastest at 0.099m3/s·a, resulting in an overall runoff change of 30.65%. On the other hand, the runoff volume under the "low-carbon" pathway shows a slow growth trend, with an increasing rate that accelerates after the mid-21st century. The runoff change rates range from 0.046 to 0.079m3/s·a. (4) Climate change will significantly alter the overall runoff conditions of the basin. With the passage of time and the increase of carbon concentration emission, the impact of temperature on basin runoff will become increasingly stronger. However, precipitation was still the dominant factor leading to changes in runoff. The overall climate environment within the basin will shift towards a warmer and wetter direction. This research will help in the future to adopt appropriate measures for soil and water conservation and ecological protection strategies in ecologically vulnerable areas affected by human activities and located in different geographical basins under the background of climate change.