Fires and floods are becoming all too common for coastal Southern California residents — but are these ‘extreme’ events likely to become even more frequent? Answering this question requires a comprehensive understanding of precipitation patterns in the region and how they are likely to change in the coming decades.

Most previous research on climate change and its impacts on streamflow has focused on drier inland regions of the southwestern U.S., but a new study from Santa Barbara Coastal (SBC) LTER scientists investigates climate change impacts on streamflow in the coastal California region, where rainfall is the dominant form of precipitation.

The study synthesized data from multiple climate and hydrologic models to better understand how climate change will affect streamflow in coastal California watersheds under two carbon dioxide emission scenarios (Representative Concentration Pathways, RCP, 4.5 and 8.5). They found that future climate conditions are predicted to produce more frequent, larger precipitation events occurring during a shorter rainy season with only a small change in annual precipitation. An increase in winter precipitation and a decrease in spring and fall was also predicted for coming decades. The duration of the wet season in the study region was an average of 124 days each year between 1961–2000. However, projected wet season length was shorter by 11 days and 18 days for 2061–2100, under RCP 4.5 and RCP 8.5, respectively.

A truck drives along a flooded street. Flood events are predicted to become more extreme and concentrated throughout this century.

Credit: Photo by Wade Austin Ellis on Unsplash

A truck drives along a flooded street. Flood events are predicted to become more extreme and concentrated throughout this century.

Enhanced precipitation extremes concentrated in a shorter period leads to more runoff and larger annual peak flows—making floods more likely. Current storm water infrastructure in Santa Barbara County lacks the capacity to handle predicted future runoff rates, which means a greater risk for flood damage. The changes in discharge and seasonality will also impact the export of nutrients and sediment to the coastal ecosystem, potentially harming coastal wildlife and ecosystem function. This study highlights a need for improvements to civil infrastructure and water resource management in the region to reduce future flood impacts.

While these results are specific to southern coastal California, they underscore the value of regional studies in determining place-specific impacts of climate projections on streamflow dynamics. Understanding these impacts will be critical for managing water resources and flood control measures into the future.

-Kristen Weiss

Source:

Feng, D., Beighley, E., Raoufi, R., Melack, J., Zhao, Y., Iacobellis, S., Cayan, D. 2019. Propagation of future climate conditions into hydrologic response from coastal southern California watersheds. Climatic Change.153: 199. https://doi.org/10.1007/s10584-019-02371-3