ESTABLISHING A BASELINE OF PAST HYDROLOGIC VARIABILITY IN SOUTHERN CALIFORNIA FOR BETTER WATER MANAGEMENT PRACTICES

Global climate change, both past, present, and future, will undoubtedly have serious impacts on the management of drought and water scarcity. Southern California is one of the most populated and, at the same time, water-poor regions in North America. It is, therefore, critical that records of past hydrologic variability are developed to provide baseline knowledge for better water management practices in future periods of diminished precipitation. Historical records of climate variability in Southern California have been maintained for less than 150 years, too short a period to provide a robust understanding of the forcing mechanisms and dynamics of multi-timescale climate variability. This interval is also too short to provide a robust, frequency distribution analysis of extreme climate-related events, such as large storms and severe droughts. In turn, the prehistoric record (>150 yrs) of climate variability in Southern California is sparsely documented, and limited to Mission diaries, tree-ring studies, some palynology, and low-resolution lake studies (Kirby et al., 2005 and references within). To improve our understanding of past hydrologic variability in Southern California, a research project involving 15 lakes is presently underway. The project's main objective is to reconstruct the baseline of past hydrologic variability, including extreme events (e.g., droughts), over a range of temporal and spatial scales. The sites range from near coast to desert and from low to high elevation. These lakes also reflect the spectrum of terrestrial ecosystems of Southern California. To date, this research has been funded primarily by regional water districts (Big Bear Municipal Water District; Lake Elsinore-San Jacinto Water Authority), which illustrates a desire for improved communication, collaboration, and cooperation between scientists, resource managers, and policy makers. Initial results from Lake Elsinore (380 masl), Big Bear Lake (2057masl), and Dry Lake (2763 masl) indicate a long-term Holocene drying trend towards the modern. More detailed sedimentological analyses from Lake Elsinore show that there is increase in the amplitude of hydrologic variability during the late-Holocene. These results may suggest that long duration droughts are a part of the modern climate system in Southern California.