Mountains of the World – Water Towers for the 21st Century (Messerli, et.al)

Bruno Messerli Institute of Geography, University of Bern Hallerstrasse 12, 3012 Bern Switzerland Abstract Mountain and Hydrology Research has a long tradition, but only the Rio Conference 1992 created a real breakthrough for a new awareness about the mountains of the world and their natural and human resources. In the years 1997 and 1998 the mountains as water towers for a thirsty planet got a special interest of the UN institutions, which led not only to the International Year of Mountains 2002 and the International Year of Freshwater 2003, but also to a better cooperation between science and policy. The particular hydrological characteristics of mountains areas are manifested by disproportionately large discharge, compared to the surrounding lowlands. Mountains account for 20-50% of total discharge in humid temperate regions, while in semi-arid and arid areas, the contribution of mountains to total discharge are 50 – 90 % with extremes of over 90 % (e.g. Nile, Colorado, Orange, Syr Daria, Amu Daria, Rio Negro etc.). Moreover , discharge from mountainous areas is highly reliable and causes significant reduction of the coefficient of variation of total discharge. These findings were quantified and used to elaborate an overall assessment of the hydrological significance of mountain areas. The dryer the lowland, the greater the importance of more humid mountain areas. Locally and regionally differentiated changes in temperature, precipitation, snow-cover and glacier storage are likely to alter discharge from mountain-dominated territories with respect to timing, volume and variability, and will influence runoff characteristics in lowlands. Catchments which are dominated by snow are particularly sensitive to climate change, and will be most affected by shifts in discharge patterns. Increasing demands on limited water resources ensure that mountains water resources will play an increasing important role in the 21st century. But we need more and better data, especially for the mountains of the tropics and subtropics, and this means for the developing world, where water scarcity means immediately food shortage. The scientific community has the responsibility to analyse the consequences and complex interactions of climate, water and land-use changes, but also of growing population and its impact on watershed management and agriculture-forestry-policy, in order to develop adequate long-term strategies on water resources management in the mountains and highlands for the surrounding lowlands.