## 4 Discussion
### Hydrological Processes and Water Availability  
Snowmelt is the dominant factor in SAM hydrological processes. Hydrograph separation via stable isotope technology in the headwaters of the Irtysh River Basin highlighted that the contribution of snowmelt to runoff reached 58.1% during the spring snowmelt period, whereas rainfall, snowmelt, and groundwater accounted for 49.1%, 36.9%, and 14.0%, respectively, of the annual runoff [33]. Global warming has made these seasonal runoff distributions highly sensitive to changes in snowpack accumulation and melting in snowmelt-fed river basins [52], and this increased sensitivity is also observed in the SAM (Figure 5). Two typical SAM basins were analyzed to investigate the hydrological effect of cryospheric change: the Kuwei national hydrological station is located in the eastern part of the SAM where there are no glaciers [33; 43], whereas the Kelatashi station is located in the western part of the SAM with this river being fed by both snow and glacial meltwater [47].  
The observed changes in the monthly runoff distributions between 1957 and 2015 at Kuwei and Kelatashi are shown in Figure 5. The maximum monthly streamflow occurred in June at both stations, with the long-term average May-July runoff accounting for 70.49% and 59.19% of the annual runoff at Kuwei and Kelatashi, respectively. The snow- and glacier-fed runoff distribution was more uniform than the runoff fed by only snowmelt because snowmelt only occurred in the spring and glacier recharge occurred mainly in the summer. The 1957-2015 cryospheric changes have led to a runoff redistribution that is represented by an increase in April and May discharge percentages, and June and July declines in the SAM (Figure 5). The earlier increase in the water supply will further aggravate the time difference between water supply and demand, which is not conducive to the sustainable and efficient utilization of water resources.  
Basins that experience significant reductions in the proportion of precipitation falling as snow may also see a reduction in their annual streamflow [53]. However, despite increased snow cover and an acceleration in glacial melting, there was no significant increase in the annual runoff between 1957 and 2015 in SAM. Variations in the observed monthly streamflow anomalies during the period 1957-2015 at the Kuwei and Kelatashi stations are shown in Figure 6. There was a significant decline in July runoff across the eastern SAM, but a general increase in spring runoff (Figure 6a), although the interannual fluctuations were amplified here by the earlier onset of snowmelt and variable accumulations (Figure 3a). Across the western SAM, runoff in spring increased significantly but then declined slightly in summer and autumn due to the earlier melting of snow cover and accelerated melting of the mountain glaciers (Figure 6b). The contribution of snowmelt will continue to expand for both 2 \({}^{\circ}\)C and 4 \({}^{\circ}\)C of warming in the SAM [52]. Although water resources have remained relatively stable in the SAM, recent cryospheric changes have led to the redistribution of these water resources, such that continued changes will amplify the challenges currently facing downstream water management.  
Figure 5: Observed changes in the monthly runoff distributions during the periods 1957–2015 at the (**a**) Kuwei and (**b**) Kelatashi hydrological stations in the SAM.  
Figure 6: Variations in the observed monthly streamflow anomalies (%) during the period 1957–2015 at the (**a**) Kuwei and (**b**) Kelatashi national hydrological stations in the SAM.