GEOG M109 Lecture 7: GeogM109Week4Lec.7
Document Summary
The principle direct human actions: irrigation agricultural lands, manipulating stream channels, damming watercourse, draining wetlands, urban and industrial consumers, extract groundwater. The indirect actions: land cover change, the spread of cities, the development of industry & agriculture. Worldwide statistics were based on fragmental initial data, expert estimations, and indirect evidence ( size of population and prevailing techniques of water supply and withdrawal). Estimation on changes in surface river runoff is based on consumptive use of freshwater and regulation of reservoirs. Estimation on base flow increases is based on regulation by reservoirs. The confidence level for estimates of changes in water regime depends on their characters. P: precipitation; e: evaporation; t: transpiration r: runoff; r=u+s s: surface runoff; u: base flow; sm: soil moisture. Direct underground runoff into oceans by paths other than rivers. Africa: 236 km3/yr: america: 344 km3/yr, america: 385 km3/yr. Total world fresh-water flows (1980) river runoff: 38,230 km3/yr,
