They are THE most important source of water during the summer. Their importance cannot be overstated. Switzerland gets 60% of its electricity from hydro power, which from spring to late autumn is glacier melt water. They replenish in winter with snowfall then slowly let the snow melt in summer. Without them we get flooding in spring and drought in autunn. The Rhine and the Po rivers, crucially important to Germany and Italy, are fed by glaciers. Italy's most productive agricultural areas are watered by the Po river. Switzerland will experience water shortages when the glaciers are gone, something the Swiss cannot fathom, because until now we always had so much water we could waste it and still have more left than we could ever use. And if Switzerland has too little water you can imagine what will happen to Italy and France.

And in Austria, some people just blew up part of a glacier to make room for a ski tournament. (sorry, no english source)

afaik they are important for the water supply of rivers in spring