Climate change has an important impact on water balance and material circulation in watersheds. Quantifying the influence of climate and climate-driven vegetation cover changes on watershed-scale runoff and sediment yield will help to deepen our understanding of the environmental effects of climate change. Taking the Zhenjiangguan Watershed in Sichuan Province, China as a case study, three downscaled general circulation models with two emission scenarios were used to generate possible climatic conditions for three future periods of P1 (2020–2039), P2 (2050–2069) and P3 (2080–2099). Differences in scenarios were compared with the base period 1980–1999. Then, a Normalized Difference Vegetation Index climate factor regression model was established to analyze changes to vegetation cover under the climate change scenarios. Finally, a Soil and Water Assessment Tool model was built to simulate the response of runoff and sediment yield in the three future periods under two different scenarios: only changes in climate and synergistic changes in climate and vegetation cover. The temperature and precipitation projections showed a significant increasing trend compared to the baseline condition for both emission scenarios. Climate change is expected to increase the average annual runoff by 15%–38% compared with the base period, and the average annual sediment yield will increase by 4%–32%. The response of runoff and sediment yield varies in different periods, scenarios, and sub-watersheds. Climate-driven vegetation cover changes have an impact on runoff and sediment yield in the watershed, resulting in a difference of 5.8%–12.9% to the total changes. To some extent, the changes in vegetation cover will inhibit the hydrological impact of climate changes. The study helps to clarify the effects of climate and vegetation cover factors on hydrological variations in watersheds and provides further support for understanding future hydrological scenarios and implementing effective protection and use of water and soil resources.

Multi-source, combined water supply models play an increasingly important role in solving regional water supply problems. At present, in the area of regional water supply, models are mainly used to study the problem of overall water guarantee rate, and do not take into account the impact of the uncertainty of multi-source water supplies on water supply risk. There is also a lack of research on how changes in multi-source water supplies affect sub-region and sub-user water guarantee rates. To address this knowledge gap, the encounter probability of different frequencies and a refined water resources allocation model of multi-source supplies were used. Using Tianjin as an example, this paper studies the quantitative relationship between the uncertainty of multi-source water inflows and the regional guarantee rate of water use. The objectives of the study are to analyze the changing trend of the water shortage rate and the main body of water supply in each region, and to quantitatively describe the influence of the variation of multi-source water supply on the main body of water supply for users. The results show that under the same requirement of guarantee rate for water use, as the number of water diversion sources increase, the probability of water supply meeting the water use rate increases significantly, and the risk to water supplies decreases. At the same time, suburban areas have a low dependence on external water supplies, while the change in the quantity of external water sources has a great impact on the water supply of the Zhongxinchengqu and Binhaixiqnu areas. The distribution and main body of water supply will change for different water users. Therefore, it is important to ensure a stable supply of external water for maintaining the guarantee rate of regional water use.

Evaluating how dams modify hydrological regimes and their long-term impacts on riverine ecosystems is critical. This study evaluated trends and change points in Fractional Vegetation Cover (FVC) of braided riverbanks downstream of the Xiaolangdi Dam (1990–2020) using time-series decomposition and structural breakpoint analysis. Distinct temporal periods corresponding to different dam construction and operational phases were identified. Partial correlation analysis and linear mixed-effects modeling were employed to elucidate the spatiotemporal linkages between FVC and key driving factors. The results identified 1997 and 2004 as significant change points in FVC, corresponding to the dam’s construction and initial interception in 1997, and its subsequent comprehensive water and sediment regulation from 2004 onwards, respectively. Although dam construction may have initially posed short-term challenges to downstream vegetation, the post-operational phase witnessed a notable increase in significant vegetation growth compared to the pre-dam period, primarily attributed to the altered hydrological conditions. Notably, the dam operation’s contribution to the total FVC increase was 56% in the near-dam Xiaolangdi–Jiahetan reach. The analysis revealed distinct differences in vegetation responses to these hydrological alterations between the upstream Xiaolangdi–Jiahetan and downstream Jiahetan–Gaocun river sections, with the latter demonstrating greater ecological sensitivity to the dam-induced hydrological changes.