River flow is a main source of freshwater both in mountain regions and downstream areas. Various sources contribute to it, including rainfall, snow and glacier melt and groundwater. Climate change affects these different sources in different ways. Climate change affects rainfall patterns, such as long-term increase or decrease, seasonal shifts or changes in rainfall intensity. Rising temperatures strongly influence snowmelt- and glacier-melt-generated river discharge; the snowmelt season starts earlier, less snow mass is available for melt, and snowmelt contribution to river flow thus decreases over the year. Whether rising temperatures produce meltwater from glaciers depends on the state and characteristics of the glaciers and the catchment basin. The concept of 'peak water' implies that, first, as glaciers shrink in response to a warmer climate, more meltwater is released until a turning point , after which glaciers melt, and so its contribution to river flow decreases. In many mountain regions worldwide, glaciers and their basins have already passed peak water, and the runoff contribution of glaciers is on the decline. Glacier shrinkage not only influences river discharge but also water quality. In the Andes of Peru, for instance, it has been observed that retreating glaciers expose bedrock, resulting in more acid water because of minerals that dissolve from the rock. Mountain ecosystems are also affected by changing freshwater availability. For instance, high-elevation wetlands in the tropical Andes critically depend on glacier meltwater during the dry season, and the disappearance of this freshwater source results in ecosystem degradation.
IPCC
Climate Change 2022: Impacts, Adaptation and Vulnerability
IPCC Report