Characteristics of Spatial and Temporal Distribution of Heavy Rainfall and Surface Runoff Generating Processes in the Mountainous Areas of Northern China

It is essential to understand the characteristics of surface runoff generating processes under different heavy rainfall events in mountainous areas. The intensity and duration of precipitation play an important role in surface runoff processes. In this study, annual rainfall characteristics from 1987 to 2023 in the Taihang Mountains were analyzed using the Pearson-III frequency curve, homogeneity tests, and the Mann–Kendall (MK) test. Four surface runoff generation events between 2014 and 2023 were monitored. The contribution of rainfall to runoff variations was quantified through the double mass curve method. Results indicate a significant increase in the frequency of moderate and heavy rainfall events over the last decade. Spatial variability of rainfall and elevation effects in the Taihang Mountains becomes less pronounced when 24 h rainfall is below 50 mm. The two surface runoff processes in 2016 and 2023 were typical runoff resulting from excess rain, which belonged to the storm runoff. The two surface runoff processes in 2021 were runoff generation under saturated conditions. For runoff generation under saturated conditions, the contribution of rainfall was only 58.17%. When the runoff coefficient exceeded 0.5, the surface runoff generating processes were entirely determined by rainfall. This study suggested that for semi-arid regions, where rainfall is unevenly distributed over the seasons, more soil water is needed to maintain local and downstream water demand during the non-rainy season. The limitations of the study are the lack of research on factors other than rainfall that intrinsically affect the surface runoff generating process.