Deltalife 13

Deltares, spring 2020 20 When the ice melts... Glaciers are important to retain fresh water. If they melt, an important water buffer is lost. What happens when climate change permanently melts more and more ice into water? This is what you need to know. By Bonne van der Veen / Photo iStock 1 One of the results of global warming is that there is less snowfall and more rain. Unlike snow, which is retained during the winter period, rain flows away rapidly. The annual discharge peak of the Rhine in Europe - which is now in late spring - ismoving to earlier in the year. Thismakes shortage of available water in the dry season more likely. Melt water from the Alpine glaciers accounts on average over the past century for just one per cent of the total discharge of the Rhine. But glaciers are an important water buffer. During dry sum­ mers, as in 2018 and 2019, melt water can account for as much as 25 per cent of the Rhine discharge. In other words, melting glaciers are an important source of water in times of drought. But the number of glaciers is falling and that process is accelerating because of global warming. There­ fore, glaciers are a finite source of fresh water. Across the world, 250 million people depend on 'water towers' for a substantial part of their water supplies: melt water from glaciers and snow packs in the upstreammountain areas of river basins. Some of these water systems are under pressure as a result of climate change and social developments. Available supplies of water (precipitation, melting snow, discharge from lakes, melting glaciers) are no longer sufficient for irrigation, industry and drinking water. Pres­ sure on water supplies in the future is increasing, particularly in parts of the Himalayas and the Andes. The Earth near the Artic is warming much faster than average. According to some climate projec­ tions, the shipping route across the North Pole will be icefree for one to twomonths annually by 2040. That may benefit international trade: this northern route reduces the time required for a trip to the east by one third compared to the traditional route through the Suez Canal. Russia has already invested heavily in a fleet of ice­ breakers to keep the route open all year round. 2 4 3