THE HYDROLOGIC CYCLE AND GLOBAL WATER RESOURCES TIBETAN PLATEAU Tibetan plateau a virtual Water Tower for Asia Temperatures here are rising twice the global average What will happen to water supply and hydrology in a warmer climate THE GLOBAL WATER CYCLE How does this thing work anyway PRECIPITATION Water holding capacity is a function of temperature Precipitation is initiated by cooling of air HOW DOES AIR COOL OFF Convective due to heating of the surface Orographic Air rises over an obstacle Convergence Air is lifted due to a low pressure zone Lifting OROGRAPHIC PRECIPITATION Tibetan plateau is dry arid Reason is partly due to orographic effects GLOBAL PRECIPITATION Annual average over land is 750 mm per year PRECIPITATION VARIABILITY Red line is global average over land DRAINAGE BASINS Land areas that drain to a speci c river INFILTRATION Water that seeps into the soil As particle size decreases i capacity of soil to hold water decreases ii maximum in ltration rate decreases TWO TYPES OF RUNOFF the stream network SLOPE AND RUNOFF As slope increases in ltration decreases and runoff increases Steep slopes produce more runoff Overland ow runoff water that cannot in ltrate into the soil ows overland until it enters STORAGE arti cial reservoirs Biggest natural reservoirs in order glaciers snow groundwater lakes soil moisture These are roughly in reverse order of ease of access ARTIFICIAL STORAGE CAPACITY Shasta Reservoir California Height 600 feet Capacity 1 265 billion gallons EVAPOTRANSPIRATION Evaporation From soil Transpiration From plants Globally 60 of precipitation over land returns to atmosphere EVAPOTRANSPIRATION REGIMES Water limited Evaporation is about equal to precipitation Increasing precipitation will increase evaporation Dry arid areas Energy limited Wet humid areas Increasing temperature will increase evaporation AVERAGE P E OVER TIBETAN PLATEAU What could this tell us about the ow paths EVAPORATION OVER OCEANS RUNOFF RATIOS The ratio of runoff to precipitation VARIATIONS IN RUNOFF RATIO Most variability explained by evaporation and soils WHAT HAPPENS IN A WARMER CLIMATE The air can hold more water Evapotranspiration will increase air water content 40 of rain over land comes from the ocean Key River ow into ocean is balanced by water vapor transport from the oceans When storms occur there is more water in the air and precipitation will increase Increasing precipitation will increase evaporation in water limited areas This leads to what is called intensi cation of the water cycle Throughout most of the Ohio River basin 2011 was the record wettest year EVIDENCE OF INTENSIFICATION Impossible to say of course PRECIPITATION FLOODING EVIDENCE OF INTENSIFICATION Impossible to say of course MISSISSIPPI RIVER FLOODING GLOBAL FLOOD DAMAGES IN 2004 7 000 deaths 116 million affected 7 5 billion in losses and damages Levee destroyed by USACE in order to save Cairo IL