Mountain systems

Abstract

Half of the human population depends on mountains. Defined by elevation above sea level (minimum between 300 and 1000 meters, depending on lati- tude), steepness of slope (at least 2 over 25 kilometers, on the 30 arc-second grid), and excluding large plateaus, mountains occupy about one fifth of the terrestrial surface. Twenty percent (1.2 billion) of the world’s human population lives in mountains or at their edges, and half of humankind depends in one way or the other on mountain resources (largely water).