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USGS Washington Water Science Center

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Marijke van Heeswijk,
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Tacoma, WA 98402

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Water Resources Inventory Area 1 Watershed Management

Introduction to Land Use and Land Cover

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Knowledge of land use and land cover is necessary to help quantify components of the water budget in the WRIA 1 study area. Land use and land cover affect evapotranspiration (defined as water evaporated from soils and wet plant surfaces and water transpired by vegetation), surface-water runoff volume and timing, and recharge of the ground-water system. For example, paved land will diminish evapotranspiration and ground-water recharge and increase surface-water runoff, and water-intensive crops will increase evapotranspiration as long as ample water is available (possibly supplied by irrigation). Dense tree cover may decrease ground-water recharge, because intercepted precipitation may evaporate before it has an opportunity to reach the ground. Land cover information can also be used to estimate irrigation and other water uses where water-use records are incomplete.

Historical land use and land cover data will be used in the next study phase to simulate historical hydrologic conditions with a computer model and by doing so learn how the water budget of the WRIA 1 study area may have changed over time. Once the computer model has been verified to adequately simulate the hydrologic system for different land uses and land covers, the model may be used to quantify the water budget of the study area for predevelopment (prior to 1850) and possible future land use and land cover conditions.

Land use and land cover data on this web page come from various sources and, as a result, similar information may have been classified differently, depending on the purpose of the classification. The most recent land use and land cover information is from satellite imagery and provides the greatest level of detail. The search for historical land use and land cover information is in progress and will be completed during the next study phase. To date (January 31, 2000), some predevelopment information has been located, but the information is insufficient to display in a map.

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