What is the water (hydrologic) cycle? Why is it important?

The hydrologic cycle http://observe.arc.nasa.gov/nasa/earth/hydrocycle/hydro2.html

The Hydrologic Cycle Water input and output is in balance globally P = R + ET

The Hydrologic Cycle Water input and output is not always in balance locally Something is missing ΔS is the change in groundwater storage P ≠ R + ET P = R + ET + ΔS

The Hydrologic Cycle Local variations can have serious consequences (floods or drought) http://observe.arc.nasa.gov/nasa/exhibits/flood/flood_1.html http://ma.water.usgs.gov/floods/flood_2006_05.html

Hydrologic Balance Measuring the amount of water coming in and going out to assess availability

Precipitation (Input) How do we measure it? Rain gauge collects 1 inch of rain. What does that mean? In a one-inch rain, what is the volume of water that falls on an area of one square mile? (Don’t have to do the numerical calculation; just outline the steps).

Measuring Precipitation (P) 1 inch = 1/12 feet 1 sq. mi = 5,280 ft x 5,280 ft = 27,878,400sq.ft. 27,878,400 sq.ft. x 1/12 feet = 2,323,200 cu.ft. 2,323,200 cu.ft. x 7.48 gal./cu.ft = 17,377,536 gals. (17 x 106 gals.) If rain fell over 1 day, the rate is 2,323,200 cu. ft. ÷ 86,400 sec/day = 26.9 cu. ft/sec.

Measuring Runoff (R) Measure how fast the water is moving in the stream (velocity, ft./sec) Measure the width and depth of the stream = area (sq. ft.) velocity depth width velocity (ft/sec) x area (sq. ft) = cu.ft/sec