The IPCC Special Report on Oceans and Cryosphere in a Changing Climate (SROCC), which was published in September and contains an extra chapter on the mountain cryosphere, provides an answer. The cryosphere is everything that is frozen, i.e. glaciers, snow, ice on rivers and lakes, frozen ground, etc.
When the snow melts in spring, there is more water in the rivers - logically. And anyone who has ever passed the same glacial stream in the morning and afternoon in summer knows that the stream has more water in the afternoon. In addition to individual precipitation events, snowmelt and summer glacier runoff determine how much water arrives downstream on many rivers.
Peak water
When glaciers shrink, there is initially more water in the runoff streams and rivers because more and more ice is melting. At some point, however, a point is reached at which the discharge volumes decrease again - less ice melts in total because there is simply not much ice left. This reversal point is often referred to as "peak water". Peak water occurs earlier on small glaciers and lasts longer on large ones. In the Alps, it is assumed that peak water has already been exceeded, at least in part, or will be exceeded before the middle of the century, as well as in other mountain regions with rather small glaciers.
Things are also changing in terms of snow. Winter runoff volumes tend to increase because more snow falls than rain and is therefore not stored in the snowpack first, but ends up in the river. The timing of snowmelt is shifting forward - probably by several weeks by 2100.