Context <p>Water conservation services (WCs), which play an important role in ecosystem hydrological processes and sustainable water resource utilization, are mainly affected by the combination of climate change and land use. However, such impacts are still not effectively differentiated.</p> Objectives <p>This study aimed to (1) reveal the year-by-year changes in WCs in the Ussuri River Basin; (2) to quantify the contribution of climatic factors and land-use changes to WCs based on the year-by-year data; and (3) to clarify the mechanisms by which climate and land-use changes act on WCs.</p> Methods <p>The relative contributions of drivers (climate change and land use) to WCs were quantified based on year-by-year series data in a typical agricultural development watershed in China (Ussuri River Basin).</p> Results <p>The mean WCs were increasing from 2000 to 2020, with an annual mean of 16.45&#xa0;mm and at an increasing rate of 0.39&#xa0;mm/year⁻¹ (<i>P</i> = 0.071). Climate change was the dominant factor in WCs, explaining 71% of the variation in WCs compared to 29% for land use. Forestland area (standardized path coefficients: <i>β</i> = 0.797, <i>P</i> &lt; 0.05) and precipitation (<i>β</i> = 0.242, <i>P</i> &lt; 0.05) had direct and enhancing effects on WCs, implying that moisture and vegetation cover play important roles in influencing WCs in this study area. Although the high proportion of cropland shows a relatively low direct correlation with WCs, its strong correlation with forestland area indirectly contributes to the enhancement of WCs. The covariance of this indirect effect is approximately 0.8, suggesting a very strong interaction.</p> Conclusions <p>Rational regulation of water availability and land-use relationships enables the restoration of WCs in agricultural areas. This study underscores the pivotal role of anthropogenic land management in sustaining ecosystem services and water resources.</p>