Abstract: Based on SWAT model, three scenarios of climate change and land use combination were set up by scenario analysis method, and the impacts of climate change and human activities on runoff in the upper reaches of the Kaidu River were quantitatively analyzed. Decision coefficient R², Nash-Sutcliffe efficiency coefficient NSE and deviation coefficient PBIAS were used as evaluation indexes of the model. The results were as followsThe model rate was 0.85, 0.84 and 6.2% for regular period, and 0.78, 0.69 and 1.6% for validation period. It showed that SWAT model was suitable for runoff simulation in Kaidu River Basin. According to the comprehensive scenario, climate change was the main influencing factor of runoff change. Under the combined action of climate change and human activities, the annual average runoff decreased by 1.83 m³/s, and climate change caused the annual average runoff decreased by 1.38 m³/s, accounting for 75.47% of the total variation. Human activities lead to a decrease of 0.45 m³/s in average annual runoff, accounting for 24.53% of the total variation. According to the extreme land use scenario, the grassland scenario reduces the annual average runoff by 0.27 m³/s, while the unused land scenario increases the annual average runoff by 1.32 m³/s; Climate change scenario showed that runoff changes were positively correlated with precipitation changes and negatively correlated with air temperature changes. The precipitation decreased by 20% and 10%, and the annual average runoff decreased by 29.31 and 14.32 m³/s respectively. Precipitation increased by 10% and 20%, and the annual average runoff increased by 15.72 and 30.91 m³/s respectively. The annual average runoff decreases by 0.58 and 1.12 m³/s when the air temperature increases by 1 and 2 ℃ respectively.

Key words: SWAT model, climate change, human activity, runoff estimation, Kaidu River Basin, scenario estimation