Climate Impacts on Streamflow Dynamics of Mammoth Creek and the Upper Owens River, California

AbstractMammoth Creek and the Upper Owens River, located in the eastern Sierra Nevada, are the primary headwater supply for Mono County and the City of Los Angeles. Population and economic growth continue to increase pressures on water supplies in the Town of Mammoth Lakes and Los Angeles, therefore a more thorough understanding on the physical processes and empirical relationships between climate and streamflow in these headwaters is warranted. Climate in the study area is characterized by large-scale features of general circulation and orography, resulting in high spatial and temporal variability. Snowmelt provides for groundwater recharge and streamflow throughout the spring, early summer, and late season low flow periods. This thesis examines how lags between climate and streamflow are related to headwater catchment geology and hydrogeology. Empirical relationships between climate and streamflow are evaluated for Mammoth Creek and the Upper Owens River with the Standardized Precipitation Evapotranspiration Index (SPEI) at 12, 15, 24, 36, and 48-month timescales, and standardized streamflows. The SPEI provides a useful basis for interpreting hydrologic regimes in this area because the impacts of climate variability on streamflow occur at a range of time scales and are largely a function of the hydrogeology. Results indicate that SPEI is well-correlated at short timescales of 12 to 15 months in granitic and alluvial watersheds of the Mammoth Creek, whereas the SPEI is well-correlated at longer time scales of 48 months in volcanic watersheds of the upper Owens River. These results paired with the hydrogeologic setting of the watersheds suggest that the relatively impermeable granitic mountain block watershed of Mammoth Creek limits deep subsurface flow and groundwater storage, while more permeable volcanic rocks of the upper Owens River allow for deep groundwater recharge, storage, and sustained baseflows. Silicate weathering of volcanic rocks, age dating of water and naturally occurring isotopes of water support the timescales identified by the SPEI. Findings from this study highlight and reaffirm the lesser known multi-time scale linkages between climate variability, hydrogeology, and hydrologic regimes of Mammoth Creek, Hot Creek and the upper Owens River using drought and streamflow indices