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Quantitatively figuring out the effects of climate and land-use change on water resources and their components is essential for water resource management. This study investigates the effects of climate and land-use change on blue and green water and their components in the upper Ganjiang River basin from the 1980s to the 2010s by comparing the simulated changes in blue and green water resources by using a Soil and Water Assessment Tool (SWAT) model forced by five climate and land-use scenarios. The results suggest that the blue water flow (BWF) decreased by 86.03 mm year−1, while green water flow (GWF) and green water storage (GWS) increased by 8.61 mm year−1 and 12.51 mm year−1, respectively. The spatial distribution of blue and green water was impacted by climate, wind direction, topography, and elevation. Climate change was the main factor affecting blue and green water resources in the basin; land-use change had strong effects only locally. Precipitation changes significantly amplified the BWF changes. The proportion of surface runoff in BWF was positively correlated with precipitation changes; lateral flow showed the opposite tendency. Higher temperatures resulted in increased GWF and decreased BWF, both of which were most sensitive to temperature increases up to 1 °C. All agricultural land and forestland conversion scenarios resulted in decreased BWF and increased GWF in the watershed. GWS was less affected by climate and land-use change than GWF and BWF, and the trends in GWS were not significant. The study provides a reference for blue and green water resource management in humid areas.

Soil erosion is recognized as one of the major environmental problems in the hilly red soil region of Jiangxi province, southern China. An eight-year field experiment was conducted to evaluate the effects of grass cover in the sloping citrus land on water and sediment runoff. Soil moisture regimes were also analysed based on the in-situ soil moisture measurement. Four treatments were carried out in the runoff plot experiment: (1) no vegetation, bare land (BL); (2) conventional treatment, citrus without grass cover (CK); (3) citrus with strip planting of Bermuda grass (SP); (4) citrus with full cover of Bermuda grass (FC). Results showed that the annual runoff volumes were significantly (P &lt; 0.05) reduced using SP (27.2 mm) and FC (33.0 mm) compared with CK (311.4 mm) and BL (456.7 mm) treatments. The SP and FC treatments significantly (P &lt; 0.05) reduced the annual average sediment yield by as much as 99.38% to 99.67%, compared with CK treatment. Soil moisture variations at the four depths (0–10, 10–20, 20–30, and 30–40 cm) were consistent with the seasonal precipitation patterns. Within the soil profile, soil moisture content increased with depth. In 3 of the 4 depths, the soil moisture contents of SP (21.20–27.84 m³/m³, mean value) were the highest. Soil moisture contents of FC (14.92–26.30 m³/m³,<br /> mean value) were lower than in SP because of the water consumption by plant transpiration, but were still higher than those of CK (16.03–25.00 m³/m³, mean value). Based on Richards’ equation numerical model, optimization tool and observed soil moisture data, actual evapotranspiration was calculated, and water balance analysis was carried out during drought and rain periods. The results indicated that planting grass in sloping citrus land can effectively reduce surface water runoff and soil erosion and increase water infiltration, but the risk of drought, resulting from planting grass, should be noticed. Compared with FC, the drought risk of SP was much lower during the drought period, and SP contributed to storage of more water in the root zone during the rain period. In conclusion, SP was a recommendable treatment.