Transcript Document
The Global Water Cycle ATMOS 397G Main Processes involved in the Water Cycle Condensation: process in which water molecules in the atmosphere change from a gas phase to a liquid phase Precipitation: process in which water falls on earth’s surface in the form of rain, snow, hail, and sleet Evapotranspiration = Evaporation + Transpiration: process where liquid water either from land surface, soil, or ocean goes back to the atmosphere as water vapor Runoff: process of water running off the land surface, occurs when precipitation exceeds evapotranspiration Infiltration: process of water seeping into the ground Groundwater flow: process that facilitates ground water coming back to the land surface ATMOS 397G Reservoirs of Available Water (liquid equivalent) on Earth Reservoir Volume (106 km3) Percent of Total Oceans 1350 97.3 Glaciers 29 2.1 Aquifers 8 0.6 Lakes 0.1 0.01 Soil Moisture 0.1 0.01 Atmosphere 0.013 (~0.3 cm rainfall) 0.001 Rivers 0.002 0.0002 Biosphere 0.001 0.0001 Residence Time 103 — 104 yr 101 — 103 yr 2 wks — 104 yr 10 yr 52 days 10 days 2 wks 6 days Based on Graedel, T. E., and P. J. Crutzen, 1993: Atmospheric Change. An Earth System Perspective. W. H. Freeman and Company. 446 pp. ATMOS 397G Water Cycle and Vegetation Actual evapotranspiration (AET) is the amount of water delivered to the air from evaporation and transpiration (water use). Potential Evapotranspiration (PET) is the maximum evapotranspiration that is expected to occur under the climatic conditions of a particular site, assuming that water is always present in the soil and plant cover is 100% (water demand) Tropical rainforests: AET = PET Deserts: AET < < PET AET is a useful predictor of net primary productivity Annual variability in AET greatest for ecosystem with low AET ATMOS 397G Transpiration of land plants important factor in determining the movement of water in the water cycle and the Earth’s climate Regional Differences in the Water Cycle Evaporation decreases from the tropics to the poles Tropics a source of water vapor in the atmosphere resulting in high salinity in tropical oceans Relative balance of precipitation and evaporation differs strongly between region on land Precipitation > evaporation in tropical rainforests runoff Precipitation = evaporation in deserts no runoff Sources of water contributing to precipitation differ in different regions Rainfall in maritime and monsoonal climates derived from evaporation from the sea Rainfall in Amazon basin derived from evapotranspiration and longdistance atmospheric-transport ATMOS 397G Total Precipitable Water Vapor Derived From The GOES-8 And GOES-10 Sounders Precipitable water is the amount of liquid water, in millimeters, if all the atmospheric water vapor in the column is condensed. This information is particularly valuable for the short-term forecasting of fog, thunderstorms and precipitation. Its accuracy is +/-10%. ATMOS 397G