Propagation of future climate conditions into hydrologic response from coastal southern California watersheds
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As a biodiverse region under a Mediterranean climate with a mix of highly developed and natural watersheds, coastal Santa Barbara County (SB), located in southern California, is susceptible to the hydrologic impacts of climate change. This study investigates the potential changes in hydro-meteorological variables in this region as well as their societal and ecological implications for projected climate conditions during the twenty-first century. Daily streamflow ensembles from 135 coastal watersheds for the period 2021–2100 are developed using the Hillslope River Routing (HRR) model forced with downscaled precipitation and temperature projections derived from 10 climate models in the Coupled Model Inter-Comparison Project, Phase 5, and two emission scenarios (Representative Concentration Pathways, RCP, 4.5 and 8.5). Analysis of the projected ensemble precipitation and streamflow series relative to historical conditions (1961–2000) shows (i) minimal change in annual precipitation (median change within ±3%); (ii) an altered seasonal rainfall distribution with a decrease in rainfall at the beginning of the rainy season (Oct–Dec), an increase during the Jan–Mar period, and a decrease at the end of the season (Apr–Jun); (iii) increases in the magnitude and frequency of large storms (> 36 mm/day) which combined with a shorter rainy season, lead to increases in annual peak flows; and (iv) the propagation of the altered precipitation characteristics resulting in nonlinear changes in the magnitude and variability of annual maximum discharges (i.e., mean, standard deviation, skew) impacting estimated return period discharges (e.g., estimated 100-year flood discharges for the period 2061–2100 under 8.5 increase by up to 185%). While these results are specific to southern coastal California, the nature of nonlinear hydrologic response to altered precipitation characteristics underscores the value of regional studies investigating potential impacts of climate projections on streamflow dynamics.
We thank Dr. David Pierce for the climate model downscaling datasets, support for which was provided by the California Energy Commission (CEC-500-10-041) and the US Geological Survey through the Southwest Climate Science Center and from NOAA through the California Nevada Climate Applications Project (CNAP) Regional Integrated Science Applications (RISA) program.
D.F., E.B., J.M. and D.C. designed the framework of this study. D.F. and E.B. wrote the paper with support from J.M. R.R. developed PET data, Y.Z. contributed to the HRR model setup, S.I. performed the precipitation and temperature downscaling. D.F. performed the model calibration, future simulations, and results analyses.
This research was supported by the Santa Barbara Area Coastal Ecosystem Vulnerability Assessment (SBA CEVA) with funding from the NOAA Climate Program Office Coastal and Ocean Climate Applications (COCA) and Sea Grant Community Climate Adaptation Initiative (CCAI), NASA’s Terrestrial Hydrology (NNX12AQ36G, NNX14AD82G) and SWOT (NNX16AQ39G) Programs, and the National Science Foundation’s Long-Term Ecological Research (LTER) program (Santa Barbara Coastal LTER—OCE9982105, OCE-0620276, and OCE-123277).
Compliance with ethical standards
Conflict of interest
The authors declare that they have no competing interests.
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