Urbanization of forest areas tends to reduce interception, reduce infiltration and increase overland flow, reduce soil-moisture storage, reduce evapotranspiration, increase runoff, increase peak flows, and reduce water quality. annual maximum peak flows, annual hydrologic responses, and annual runoff were found (from actural streamflow records) to increase with progressive urbanization. the percentage of summer rainfall that appeared as runoff and the hydrologic responses were greater for partially urbanized watersheds than for mostly forested ones.

S2Urbanization, particularly in the crowded Northeast, has created a new environment. Asphalt and concrete have replaced hundreds of square miles of soil, buildings have replaced trees on much of the land, and sewers have replaced streambeds in many areas. As a result, the hydrology of this land is changing rapidly. To determine the effects of this expanding urbanization on forested watersheds, the Northeastern Forest Experiment Station has studied streamflow records of forested and urbanized watersheds. This paper is a report of that study. We consider first the urban and forest environments in relation to their differing effects on several hydrologic processes and on water quality. Second, we estimate the effects of urbanization on evapotranspiration and runoff by theoretically imposing urban conditions on a forested watershed for which climatic and streamflow records are available. Third, we describe the effects of actual progressive urbanization on peak flows, stormflows, and annual runoff of three Northeastern watersheds; and we compare peak flows, percentage of runoff, high- and low-flow intervals, and hydrologic responses between four partially urbanized and nine mostly forested watersheds. S3.

Of all the outputs of forests, water may be the most important. Streamflow from forests provides two-thirds of the nation's clean water supply. Removing forest cover accelerates the rate that precipitation becomes streamflow; therefore, in some areas, cutting trees causes a temporary increase in the volume of water flowing downstream. This effect has spurred political pressure to cut trees to increase water supply, especially in western states where population is rising. However, cutting trees for water gains is not sustainable: increases in flow rate and volume are typically short-lived, and the practice can ultimately degrade water quality and increase vulnerability to flooding. Forest hydrology, the study of how water flows through forests, can help illuminate the connections between forests and water, but it must advance if it is to deal with today's complexities, including climate change, wildfires, and changing patterns of development and ownership. This book identifies actions that scientists, forest and water managers, and citizens can take to help sustain water resources from forests.