Climate Change Suppresses Santa Ana Winds of Southern California and Sharpens Their Seasonality

Abstract

We downscale Santa Ana winds (SAWs) from eight global climate models (GCMs) and validate key aspects of their climatology over the historical period. We then assess SAW evolution and behavior through the 21st century, paying special attention to changes in their extreme occurrences. All GCMs project decreases in SAW activity, starting in the early 21st century, which are commensurate with decreases in the southwestward pressure gradient force that drives these winds. The trend is most pronounced in the early and late SAW season: fall and spring. It is mainly determined by changes in the frequency of SAW events, less so by changes in their intensity. The peak of the SAW season (November–December–January) is least affected by anthropogenic climate change in GCM projections.

Santa Ana Winds of Southern California Impact PM2.5With and Without Smoke From Wildfires

“…Recent work suggests that wildfire severity and risk specifically in SoCal will likely intensify in the warming future, while gradually shifting from fall to winter (Williams et al, ). This seasonal shift is associated with a projected weakening of SAW activity, particularly in the fall and spring (that is coincident with a projected decrease in fall precipitation; Pierce et al, ; Swain et al, ; and thus more likelihood of dry fuels persisting into winter) and a sharper seasonal SAW peak in December (Guzman‐Morales & Gershunov, ).…”

“…Examination of projected health risks due to future wildfire risk and changes in SAW is warranted. Confounding the smoke‐health impacts associated with SAW and wildfires, SAW also drive coastal heat waves that incur their own health risks (Kalkstein et al, ), which will change in a warmer future as SAW‐driven heat waves become less frequent (Guzman‐Morales & Gershunov, ) but hotter (Hughes et al, ). The ventilation effect of SAW without wildfires, meanwhile, should be beneficial to respiratory health—a hypothesized effect to be examined and quantified in future research.…”

Observed Impacts of Anthropogenic Climate Change on Wildfire in California

“…There has been no observed statewide or regional trend in the number of fall days with high (top 15%) FFWI values Earth's Future (Figure 6c) or in the mean FFWI among of the most intense 10 FWI days per fall ( Figure S21a) since at least 1958, when our FFWI records begin ( Figures S17-S20). Extending the records from those studies through 2018, there were no significant trends in fall Santa Ana frequency or intensity since the mid-1900s ( Figure S22), despite projected negative trends (Guzman-Morales & Gershunov, 2019;Hughes et al, 2011). Extending the records from those studies through 2018, there were no significant trends in fall Santa Ana frequency or intensity since the mid-1900s ( Figure S22), despite projected negative trends (Guzman-Morales & Gershunov, 2019;Hughes et al, 2011).…”

“…However, many climate models have systematic biases in North Pacific storm tracks and tropical Pacific sea surface temperatures that should lead to strong skepticism regarding model simulations of future precipitation in California (Seager et al, 2019;Simpson et al, 2016). In fall, models project reduced frequency and intensity of Santa Ana wind events (Guzman-Morales & Gershunov, 2019;Hughes et al, 2011). In fall, models project reduced frequency and intensity of Santa Ana wind events (Guzman-Morales & Gershunov, 2019;Hughes et al, 2011).…”

“…Climate models also project precipitation frequency declines in spring through fall that would partly offset winter increases, resulting in increased precipitation variability (AghaKouchak et al, 2018;Pierce et al, 2018;Polade et al, 2014;Polade et al, 2017;Swain et al, 2018). However, concurrent warming and decreased fall precipitation may, to some degree, counteract the effects of reduced offshore winds on fall fire risk in southwestern California (Hughes et al, 2011;Pierce et al, 2018), possibly extending the fire season towards the winter peak of the downslope wind season (Guzman-Morales & Gershunov, 2019;Syphard et al, 2018). However, concurrent warming and decreased fall precipitation may, to some degree, counteract the effects of reduced offshore winds on fall fire risk in southwestern California (Hughes et al, 2011;Pierce et al, 2018), possibly extending the fire season towards the winter peak of the downslope wind season (Guzman-Morales & Gershunov, 2019;Syphard et al, 2018).…”