Rainfall and Runoff
Published Online: 15 JUL 2005
Copyright © 2005 by John Wiley & Sons, Inc.
How to Cite
Endreny, T. A. 2005. Rainfall and Runoff. Water Encyclopedia. 4:315–319.
- Published Online: 15 JUL 2005
Rainfall is generated by multiple weather patterns, summarized into frontal, orographic, and convective, that affect the duration and intensity of storm accumulation. Climate data analyses reveal regional and local trends in the seasonal and annual rainfall patterns of duration and intensity and have been reported in map and tabular form for durations of 5 minutes to 24 hours and a variety of return periods in Technical Papers 40 and 49 by the U.S. Weather Bureau and in HYDRO-35 by the National Weather Service. A large variation in rainfall spatial and temporal duration and intensity has been observed for large and small area, long and short time events, and a combined system of drop-size spectrometers, recording rain gauges, and microwave radar have helped to capture this detail nationally at the resolution of 5 minutely volume scans for 1 km2 bins, aggregated to rain-gauge-corrected hourly totals at 4 km2 bins. Internal warm and cold cloud precipitation dynamics, low-level evaporation of falling precipitation, and distinction between rain, sleet, freezing rain, and snow still provide technological challenges. Time series plots of rainfall are referred to as hyetographs, maps of equal rainfall amounts are known as isopleths, and National Weather Service NEXRAD Doppler radar gauge-corrected hourly 4 km2 grid based rainfall maps are known as Stage III products. The spatial aggregation of rainfall point estimates from rain gauges is performed using surface fitting, weighting, and interpolation schemes, including the method of Thiessen polygons.
- variable source area;
- runoff ratio;
- water year