Abstract: Studying the relationship between rainfall and runoff in river basin provides a basis for reasonable water resources management and soil and water conservation. Based on measured rainfall data and historical measured runoff data in the Balegen River basin, SWAT model was constructed and was used to restore runoff series. The interannual variation characteristics and trend of rainfall-runoff relationship from 1970 to 2015 were examined using Kendall rank test, moving average, M-K test, wavelet analysis, cumulative anomaly method, and runoff coefficient analysis. Furthermore, the contribution rate of climate change and human activities to runoff changes were quantitatively separated by comparing the cumulative slope change rate. Results manifested that 1) SWAT model is feasible to restore the runoff in Balegen River basin, with the evaluation index R² reaching 0.78 and NSE 0.76 in calibration period, and R² 0.58 and NSE 0.51 in verification period. 2) From 1970 to 2015, rainfall in the Balegen River basin displayed a significant upward trend, while runoff trend was not significant; rainfall changed abruptly in 1981, and runoff in 1995 and 2010. The periodicity of rainfall and runoff series varied especially in the principal cycle; the principal cycle of rainfall is 28 years and runoff 23 years. 3) The rainfall-runoff relation changed abruptly in 1989 and 2001, after which the overall runoff coefficient declined, from 0.15 in 1970-1988 to 0.11 in 1989-2006, and 0.10 in 2007-2015. 4) With 1970-1988 as the base period, human activities dominated the runoff change from 1989 to 2001 with a contribution rate of 65%, and climate change contributed 35% to the runoff change; human activities also contributed 81% to runoff change from 2001 to 2015, and climate change contributed 19%. When 1989-2001 was determined as the base period, the contribution rate of human activities to runoff change from 2001 to 2015 was 51%, and the contribution rate of climate change was 49%.

Key words: rainfall-runoff relation, SWAT model, change of trend, comparison of cumulative slope change rate, runoff restoration, Balegen River