HR: 0800h
AN: H51D-1179    [Abstracts]
TI: Anthropogenic changes to the hydrologic regime and potential effects on anadromous salmonids in California south of the timber forests
AU: * Deitch, M J
EM: mdeitch@berkeley.edu
AF: Department of Landscape Architecture and Environmental Planning, University of California, Berkeley, 200 Wurster Hall, Berkeley, CA 94720-2000 United States
AU: Kondolf, G M
EM: kondolf@berkeley.edu
AF: Department of Landscape Architecture and Environmental Planning, University of California, Berkeley, 200 Wurster Hall, Berkeley, CA 94720-2000 United States
AB: Though the natural range of anadromous salmonids on the Pacific coast of North America extends from Alaska to Baja California, most studies to identify factors that affect their viability in coastal watersheds are conducted in timber-dominated catchments from northern California into Canada. These studies have focused especially on anthropogenic additions of fine sediment as limiting salmonid survival. South of the timber forests, the availability of water may be more important than sediment for affecting salmonid viability. The potential influence of human water demands on the natural hydrologic regime may be greater in central California than in the Pacific Northwest because of less total annual rainfall and the persistent drought that occurs from May through September (when human water needs are greatest). Identifying human-caused impacts requires a thorough understanding of regional climate and hydrology, which vary widely across temporal scales (from one year to the next, across seasonal gradients, and even over a daily scale), and across spatial scales as well. By examining historical stream flow and precipitation records, we characterize the effects of the climate on stream flow, and how these effects vary through the drainage network: more than 50% of annual precipitation is transferred to runoff in an average year, but only 5% of this runoff occurs between May and September. Manipulations in the hydrologic regime may affect winter flows, when salmonids need different water levels for passage, spawning, and channel maintenance; but they may have a more profound and widespread effect on spring and summer flows, when water is needed for juvenile rearing. By examining historical stream flow records and documented demands of stream water for human use, we identify the short-term and long-term impacts (through measures of intensity, persistence, and frequency) of potentially adverse conditions to various stages of the salmonid life cycle that manipulations to the natural hydrologic regime may cause as a result of water use. Analyses considering the spatial and temporal variations of the hydrologic regime, and the potential impacts that human water demands may place on natural hydrologic processes, are essential for planning restorative practices and for developing management plans for coastal watersheds throughout this region.
DE: 1803 Anthropogenic effects
DE: 1812 Drought
DE: 1836 Hydrologic budget (1655)
DE: 1860 Runoff and streamflow
DE: 1884 Water supply
SC: Hydrology [H]
MN: 2004 AGU Fall Meeting