Evolution trend of snow cover and simulation of snowmelt runoff in upper reaches of Lancang River

Affected by global climate change, the variations of snow cover and snowmelt runoff in the high cold region has raised an increasing concern. Snowmelt water is an important component of spring runoff in the Lancang River basin, and it is of great significance for the scientific operation of cascade hydropower stations in the Lancang River basin to master the variation law of snow cover in the upper reaches of the Lancang River and accurately simulate the snowmelt runoff process. Based on the remotely sensed snow cover data from 2000 to 2019, the Mann-Kendall trend test method was used to analyze the spatio-temporal variation of snow cover in the upper reaches of Lancang River. An snowmelt runoff model was established, and the PSO algorithm was introduced to determine the model parameters to simulate the snowmelt runoff process. The results show that the snow cover in the upper reaches of Lancang River showed no significant increase in spring, autumn and winter, and no significant decrease in summer. The average annual snow cover in spring, summer, autumn and winter was 0.16, 0.06, 0.13 and 0.17, respectively. The snow cover in the southwest and north of the Lancang River source area increased in all seasons, while the snow cover in the southeast area decreased. Among them, the increase of snow cover in the northwest reaches the largest in winter, up to 3%/a. The SRM model has good applicability in the upper reaches of the Lancang River, and the certainty coefficients of calibration period and verification period are 0.87 and 0.78, respectively, and the results have a certain implication for the simulation of snowmelt runoff in the alpine region.