Stories From The Field

Assessing the Impact of Impervious Surfaces on Water Resources in Southern California

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Water is one of the most important natural resources in the Southern California region, and natural vegetation plays a large role in managing the region’s water supply. When natural vegetation is replaced with impervious surface, the natural hydrology cycle is altered, increasing stormwater runoff and reducing groundwater recharge. The result is more frequent flooding, higher flood peak flow, lower base flow in streams, and lower water table levels.


To analyze how the natural vegetation of an area has changed over time, the Global Ecosystem Center (GEC) used NOAA’s Coastal Change Analysis Program (C-CAP) land cover data sets from 1996, 2001, and 2005. C-CAP provides a nationally standardized source for accurate baseline information, and because all C-CAP data sets were created using the same criteria and standards, they can be compared against one another to document changes over multiple years. With these standardized data sets as a guide, GEC used additional archived Landsat imagery from 1984 and 2011 to identify changes in impervious surface over a longer time span. An urban ecosystem analysis was also used to calculate impacts of land cover change on stormwater runoff.


The land cover change analysis using C-CAP data and the extended GEC land cover classifications show that there has been tremendous growth in impervious surface in Southern California over the 26 year period. This information allows decision-makers to geographically pinpoint where impervious surface increase is altering the natural hydrology of the region so that they can develop better strategies for land use and natural resource management.

The San Diego sub-basin has seen growth in urbanized areas over the past two decades. Change areas between 1985 and 2011 are represented in turquoise.
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