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The middle and upper reaches of the Han river are involved in the South-to-North Water Diversion Project, and the change of runoff affects the amount of adjustable water. In order to investigate the change of runoff in the middle and upper reaches of the Han river basin under climate change, based on the SWAT (Soil & Water Assessment Tool, SWAT) model, we have developed a new model, which is based on the Soil & Water Assessment Tool (SWAT), five global climate models and four Shared Socioeconomic Pathways (SSPs) scenarios are simulated under future climate scenarios (2021-2021) in the upper and middle reaches of the Han river Basin. Based on the SWAT (Soil & Water Assessment Tool) model, we applied five global climate models and four Shared Socioeconomic Pathways (SSPs) scenarios from the latest 6th Coupled Model Intercomparison Project Phase 6 (CMIP6), and simulated the temporal and spatial changes of runoff in the middle and upper reaches of the Han river basin in the near term (2021-2040), middle term (2041-2060), and long term (2061-2080) under the future changes of climate scenarios. The results showed that: (1) compared with the baseline period (2000-2014), rainfall and temperature increased significantly under all model scenarios, and under the "two-carbon" scenario, the increase in temperature and precipitation was smaller than that of the high-carbon scenario, and the watershed was developing towards wetting and warming. (2) The future runoff in the study area showed a significant increasing trend under the SSP2-4.5 and SSP5-8.5 pathways, relative to the historical period, and the runoff decreased in some years in the upstream near, middle and far periods. 8.5 pathways show a significant increasing trend, relative to the historical period, and runoff decreases in some years in the upstream near-, mid-, and far-periods. (3) Intra-annual distribution was more even, and runoff increased during the dry period from November to June of the following year, which improved the drought-resistant capacity of the basin. (4) Spatially, the increase in runoff was dominated by the central and eastern parts of the country, and runoff decreased under the high-carbon scenario in the near future, but showed an increasing trend in the long term, with an increasing trend in future runoff at the source area of the South-to-North Water Diversion Project. [ABSTRACT FROM AUTHOR]

Blue-green water evaluation can provide scientific suggestion for the comprehensive management of water resources in the basin. Here Wujiang river basin was as an example, based on the SWAT (Soil and Water Assessment Tool) hydrological model, the annual runoff anomaly percentage method was used to determine different precipitation patterns. The Mann-Kendall trend method(M-K) and the linear regression trend analysis method were applied to evaluate the temporal and spatial characteristics of blue-green water resources from 1992 to 2019 and the differences in the distribution and spatial distribution of blue-green water in different precipitation years. The results showed that: (1) the simulation of the SWAT model was better, which describe the water cycle process in Wujiang river basin. (2) The annual average precipitation, blue water resources and green water resources in the basin were 1126mm, 549mm and 589mm, respectively. The precipitation and blue water resources generally showed a decrease trend, but the green water resources exhibited an increase trend. (3) The green water coefficient were 46%, 52% and 58% in the wet year, normal year and dry year, respectively. Thus, the amount of green water resources has changed and plays an important role in ecosystem maintenance. (4) From the upstream to the downstream of the basin, the precipitation and blue water resources increased first and then decreased, while the green water resources presented a trend of first increasing, then decreasing and finally increasing. (5) The temporal and spatial variation of blue water resources was mainly impacted by the change of precipitation, while that of green water resources was affected by the change of precipitation, temperature, and land use cover. [ABSTRACT FROM AUTHOR]