The effects of watershed urbanization on the stream hydrology and riparian vegetation of Los Peñasquitos Creek, California

We investigated the effects of watershed urbanization on streamflow characteristics and the riparian vegetation community of Los Peñasquitos Creek, in coastal Southern California. We used stream gage records to assess streamflow changes and historic aerial photographs to measure land use and riparian vegetation changes in the watershed. During the period 1966–2000, urban land uses increased from 9% to 37% of the watershed. Over the same time period, median and minimum daily discharges, dry-season runoff, and flood magnitudes in Los Peñasquitos Creek increased significantly. Altered channel geomorphology and a doubling of the area of riparian vegetation accompanied changes in streamflow characteristics. The increased area of impervious surfaces and imported municipal water supplies associated with urbanization in the watershed have driven changes in the historic riparian vegetation community by altering streamflow characteristics and channel geomorphology. Thus, watershed urbanization in coastal Southern California can significantly modify the character and integrity of stream and riparian ecosystems, which has significant implications for their conservation in the light of rapid pace of urbanization in the region.