Future changes in runoffs in the headwaters of the Tarim River

The Tarim River Basin, situated in the Eurasia hinterland, serves as the heart of China’s Silk Road Economic Belt. It covers an area of 1.02 million km² and is surrounded by the Tienshan Mountains to the north, the Kunlun Mountains to the south and the Pamir to the west. The runoff is recharged by glacier melt, snow melt, and rainfall. There are large amount of glaciers distributed in the high mountains of Tienshan and the Kunlun Mountains. In recent decades, the glaciers in the Tienshan Mountains are retreating at a faster rate, while glacier in the Kunlun Mountains show less retreat or even advancing trend (i.e., Karakorum anomaly). These changes in glaciers will definitely alter the future runoff.

This study extended the hydrological model SWAT-Glacier by incorporating a degree-day based glacier melt and accumulation module. The hydrological processes of the headwaters of the Tarim River were simulated using SWAT-Glacier model. The model was calibrated and validated using multiple variables, including glacier mass balance, snow cover area, snow water equivalent, daily streamflow and the balance between snowfall, snow melt and sublimation. The hydrological model was forced by the bias-corrected climate from 6 regional climate models in CORDEX. Results indicated that the runoffs of the headwaters originated from the south Tienshan Mountains (i.e., Kaidu River, Aksu River) demonstrated a slight increase or even decrease trend. For the Kaidu River, there will be a slight decrease in runoff under SSP585, as the contribution of glacier melt water is less than 10%. For the Kumarak River, the runoff showed slightly increase and the glacier melt runoff will reach peak point before 2050s. For the rivers originated from the north Kunlun and Karakorum Mountains, the runoff will increase dramatically.

This study provide a basin-scale runoff changes under multiple constraints in the endoreic Tarim River Basin. However, the glacier accumulation and ablation suffers from great uncertainty as the precipitation observation is rare in the high mountains. More efforts should be taken to utilize more state-of-the-art technology in revealing the meteorological and hydrological processes in these alpine catchments.