Attribution analysis of annual average runoff depth variation in the upper reaches of the Bao River based on the Budyko hypothesis

In recent years, the shortage of water resources in Beijing-Tianjin-Hebei region has an important impact on the ecological environment. In order to quantify the impact of human activities and climate change on water resources, the authors in this article conducted an attribution analysis of runoff changes in typical small watersheds in the northern mountainous areas of Beijing-Tianjin-Hebei water conservation area. Based on the data of precipitation, evaporation, and runoff in the upper reaches of the Bao River from 1981 to 2020 and the Mann Kendall method (M-K method), the baseline period was determined from 1981 to 2006 and the variation period was determined from 2007 to 2020. The results show that the annual average runoff depth during the variation period decreased 46.47 mm compared with the baseline period, accounting for 77.10% of runoff the total depth during the baseline period. Based on Rescaled Range Analysis (R/S), the future annual average runoff depth of the upper reaches in the Bao River was deduced to keep an opposite changing trend compared with the annual average runoff depth from 1981 to 2020, showing a stable increasing trend. Based on the Budyko hypothesis principle, the impact of climate change and human activities on the annual runoff depth in this region was quantitatively evaluated. The contribution rate of climate change to the runoff depth was 40.29%, and the contribution rate of human activities to the runoff depth was 59.71%. The impact of human activities on the runoff depth is mainly through changes in the land use type. A total of 30.28% of the land in the study area has undergone mutual transformation, with an increase of 67.61% in tree forests in 2020 compared to 1985, which greatly enhanced the water conservation capacity of the study area. The increase on vegetation coverage also reduces the potential evaporation. The research results could enhance the understanding of hydrological and water resources in the hilly areas of the northern Beijing-Tianjin-Hebei region, and provide some references for screening the driving factors of water source conservation function in Beijing-Tianjin-Hebei region.