ABSTRACT Map of Erguna River right bank with sub-basins, stations, climate trends (warmer, drier, higher evaporation), declining runoff coefficient, and land use pie chart. The right bank of the Erguna River Basin, a critical transboundary region between China and Russia, plays a vital role in regional water security and ecological stability. Using hydrological and meteorological data from 1957 to 2018, this study systematically investigates the drivers of declining runoff efficiency through trend analysis, spatial interpolation, and runoff coefficient evaluation. Results reveal significant spatial heterogeneity. The multi-year average runoff coefficients for the primary runoff-generating areas of the Hailar, Gen, and Jiliu Rivers are 0.193, 0.345, and 0.434, respectively. Over the 62-year study period, the runoff coefficient declined across the entire basin, with the Hailar River Basin experiencing the largest reduction (21.7%). Notably, while total runoff showed no significant trend, the runoff coefficient decreased significantly, indicating fundamental changes in the rainfall-runoff relationship. Climate change emerges as the dominant driver: temperature increased by 0.34°C/decade, relative humidity decreased by 1.04%/decade, leading to a significant increase in atmospheric evaporative demand, as indicated by a 21.5 mm/decade rise in pan evaporation. This heightened evaporative demand has exacerbated soil moisture deficits, thereby altering the rainfall-runoff relationship and reducing the proportion of precipitation converted to runoff. Concurrently, land use changes and human activities have also influenced surface runoff capacity.
Sun et al. (Fri,) studied this question.