Annual runoff coefficient variation in a changing environment: a global perspective

Abstract

Abstract Assessing variations in the annual runoff coefficient (RC) on a basin scale is crucial for understanding the hydrological cycle under natural and anthropogenic changes, yet a systematic global assessment remains unexamined from a water-balance perspective. Here, we combine observation-based runoff and precipitation datasets to quantify basin-averaged RC changes in 433 major global river basins during the period 1985–2014. Thereafter, the ratios of terrestrial water storage changes and evaporation to precipitation (SC and EC, respectively) are obtained to evaluate the factors driving the RC changes. The results show that 12.93% of the basins experience significant decreasing trends in RC, with slopes ranging from −0.55 ± 0.17% yr−1 to −0.05 ± 0.02% yr−1, while 6.47% basins show increasing RCs with slopes ranging from 0.09 ± 0.04% yr−1 to 0.56 ± 0.17% yr−1. A higher percentage (62.95%) of basins reveal decreasing RCs for the regions with considerable human intervention compared to those (58.24%) with dominant natural variability. Changes in EC dominate the RC changes over 79.68% of the basins for both increasing and decreasing trends, with a maximum contribution (53.65%) from transpiration, among other partitioned components. Corroborated inferences from explicit investigation in the Yangtze River basin highlight the robustness of our results for global water managers and policymakers.