Melt water from mountain snow and glaciers contributes significantly to river flow and water resources in many parts of the world. An estimated one-sixth of the world's population depends on snow-and ice-melt for their water supply. Evidence of accelerated melting in most mountain systems, coupled with globally increasing demands for fresh water, has highlighted the importance of this vital source and the vulnerability of downstream communities to the potential impacts of climate change. Understanding, and reliably predicting, the quantity, timing and variability of runoff from mountains is essential to safeguard the lives and future livelihoods of many millions of people around the world.
Interactions between the processes that control the snow-and ice-melt contribution to runoff vary considerably between different climatic regions. In mid-and high-latitude mountain ranges, for example, seasonal snow cover exerts a strong influence on runoff variability, whereas glaciers are the dominant source of water during the dry season at low latitudes. Consequently, climate change is expected to trigger different responses in different regions.
A symposium on the Contribution from Glaciers and Snow Cover to Runoff from Mountains in Different Climates was held to address these issues during the 7th Scientific Assembly of the International Association of Hydrological Sciences (IAHS) in Foz do Iguaรงu, Brazil (4-9 April 2005). The symposium was convened by the former International Commission on Snow and Ice (ICSI), which now has become the Union Commission of Cryospheric Sciences (CCS). Snow and ice hydrology as a research emphasis continues in the IAHS as the new International Commission on Snow and Ice Hydrology (ICSIH), with strong links to CCS. Selected papers from the symposium have been compiled for this Special Issue. The papers address the influence of present climate, and the potential effects of climate change, on snow-and ice-melt runoff in several different parts of the world, ranging from analyses of historical data to future predictions, driven by climate model output. It is apparent that severe consequences of enhanced melting may be expected on a decadal time-scale and that further quantitative predictions of the effects of snow-and ice-melt on runoff are needed. Much uncertainty remains owing to the lack of data of sufficient length, and quality, for trend analyses, model input and model validation, particularly in the Andes, Himalaya and Arctic.