An integrative analysis of hydroclimatic elements in the three-river source region for historical and future periods: Shift toward an intensified hydrological cycle

The Three-River Source Region (TRSR), China's water tower and an important ecological barrier in China, provides a considerable amount of water to the downstream regions, home to more than 500 million people. The present study focused on the assessment of hydrological components (i.e., precipitation, actual evapotranspiration, potential evapotranspiration, surface flow, baseflow, streamflow, soil moisture, snowmelt water, and terrestrial water storage), their transformation and trends along with meteorological elements (i.e., maximum temperature, minimum temperature, mean temperature, relative humidity, wind speed, and sunshine hours) in the historical and future periods. For this, the hydrological model, HEC-HMS, was applied to simulate hydrological components and Mann-Kendal to explore the trends for 1981–2015. First time, the statistical downscaling model, SDSM, was used to generate climatic data under the shared socio-economic scenario-5 (SSP585) in the region, which was applied to simulate the hydrological cycle. The assessment results showed that precipitation transformed into evapotranspiration and streamflow by 70 % and 30 %, respectively. In the region, streamflow was generated by 78 %, 22 %, and 5.6 % by baseflow, surface flow, and snowmelt. According to trend results, all climatic variables showed statistically significant trends but insignificant in all hydrological components for the historical period, except evapotranspiration. However, all hydroclimatic components were projected to increase in the future, except windspeed. For example, temperature, precipitation, evapotranspiration, streamflow, and direct flow (surface flow) will increase by 1.4 (3.3) °C, 12 (36) %, 8.5 (19) %, 25 (95) %, and 77 (473) % in 2021–2060 (2061–2100) relative to 1981–2020, which shows, the region will be hotter and wetter, with high flooding potential in the future. These results will be helpful for precise water resources planning and management in this extremely sensitive region to climate change.