HYDROLOGIC SENSITIVITY OF THE SOUTHERN SIERRA NEVADA CRITICAL ZONES TO CLIMATE CHANGE PROJECTIONS

In order to examine the hydrological system sensitivity of the southern Sierra Nevada critical zone areas to climate change scenarios (CCS), five headwater basins of the snow-dominated Upper San Joaquin River Watershed (USJRW) were selected for hydrologic simulations using the Hydrological Simulation Program-Fortran (HSPF) model. A pre-specified set of CCS as projected by the Intergovernmental Panel on Climate Change (IPCC) were adopted as inputs for the hydrologic analysis. These scenarios include temperature increases between 1.5 and 4.5 C^oand precipitation variation between 80% and 120% of the baseline conditions.

The historical meteorological data from a NOAA station at CA049855 were used, which were available for the period from 1970 to 2005. The measured data include precipitation, air temperature, wind speed, solar radiation, potential evapotranspiration (ET), dewpoint temperature and cloud cover. The daily discharge data were obtained from the USGS real-time stream gauging station No.11226500 which maintained a 47-year record from 1921 to 1991 with missing data from 1929 to 1951. Statistical analyses show that there is a strong and continuous temperature increase during the past few decades from 1970 to 2005. The 5-year running mean temperature increased from 10 C^o to 12 C^o.

The HSPF model was calibrated and validated with measured historical data. It was then used to simulate the hydrologic responses of the watershed to the projected CCS. Results indicate that the streamflow of USJRW is sensitive to the projected climate change. The total volume of annual streamflow would vary between -41% and +16% compared to the baseline years (1970–1990). Even if the precipitation remains unchanged, the total annual flow would still decrease by 8–23% due to temperature increases. A larger portion of the streamflow would occur earlier in the water year by 15–46 days due to the temperature increases, causing higher seasonal variability of streamflow.