1. The Regional Context

The Karakoram Himalaya comprises the highest, most heavily glacierised watersheds of the upper Indus and Yarkand River basins. It is set within other vast mountain systems of High Asia that support more than 100,000 km² of perennial snow and ice cover. The chapter situates the Karakoram in this Central Asian context and outlines key aspects of the regional environment. A variety of other cold region or cryosphere features are of interest including seasonal snow covers and perennially frozen ground or permafrost. These affect much greater areas than the glaciers, as do periglacial conditions and snow avalanches. Rock glaciers are concentrated in some parts, periglacial systems closely related to glaciation in distribution, climate responses and genesis. Two main aspects of the Karakoram environment are reviewed: the region’s geology and geotectonic evolution, and its climate. The glaciers would not exist at all, or be so extensive, without the great elevations created by mountain-building forces. Significant aspects of their morphology and behaviour relate to rugged, steep landscapes developed through deep dissection by rivers and past glaciations. The Karakoram climate is influenced by three seasonally varying weather systems: the predominantly winter Westerlies, the summer monsoon and Inner Asian high-pressure systems. The glaciers are affected by each system, their relations to one another, by their strong year-to-year variations and how, in turn, they are influenced by the high mountain terrain. In the lower Karakoram valleys and surrounding high plateaux, dry conditions are found, including where most weather stations are located. However, the glacierised area is, in fact, largely humid. Measured snowfall and water yields from glacier basins challenge a long-held view of the Karakoram as part of what has been termed ‘the semiarid Himalaya’. Snowfalls in glacier source areas are in the range 1,000–2,000 mm water equivalent. Also, summer snowfall at high elevations will be shown to be a major factor in sustaining the glaciers, whereas winter precipitation dominates in weather station records. Estimates of the much-studied snowlines are shown to be problematic since they occur where freeze–thaw cycles, wind and avalanche redistribution of snow, are concentrated. The importance of Karakoram glaciers for the flows of the Yarkand River and main stem of the Indus is outlined.