Effect of Reduced Summer Cloud Shading on Evaporative Demand and Wildfire in Coastal Southern California

Williams, A. Park; Gentine, Pierre; Moritz, Max A.; Roberts, Dar A.; Abatzoglou, John T.

doi:10.1029/2018gl077319

Cited by 26 publications

(28 citation statements)

References 52 publications

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“…The Santa Monica Mountains and greater Simi Valley experienced the most repeat fire driven by Santa Ana winds, and had little evidence of non-katabatic large fire growth, consistent with prior assessments of high fire danger during Santa Ana conditions [26,27]. As there is a high rate of fire ignitions in the study area due to high human population density [5], this may suggest that fires occurring under non-katabatic conditions are easily suppressed, due to factors such as relatively high fuel moisture associated with the marine layer [28]. Additionally, the spatial dichotomy of these fire regimes is likely also a byproduct of the seasonality of extreme fire danger, defined by days where the Burning Index calculated using the US National Fire Danger Rating System and a gridded surface meteorological dataset [29] from 1979-2017 exceeds the 95th percentile.…”

Section: Fire Frequency and Patternsupporting

confidence: 67%

Spatial Distribution of Wildfires Ignited under Katabatic versus Non-Katabatic Winds in Mediterranean Southern California USA

Kolden

Abatzoglou

2018

Fire

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Wildfires are a major hazard to humans in the southern California Mediterranean ecosystem and improving our understanding and delineation of different fire regimes is critical to mitigating wildfire-related hazards. Recent research has demonstrated that there are two distinct fire regimes in this region based on the presence or absence of katabatic winds (primarily Santa Ana winds) concurrent with the fire. Here, we expand the katabatic wind category to include Sundowner winds along the Santa Barbara front range and analyze the spatial relationships and difference in ignition sources between fires associated with katabatic and non-katabatic wind events from 1948-2017. We found distinct spatial extents for katabatic versus non-katabatic fires, with areas of the higher number of repeat fires generally associated with one fire type or the other. These spatial delineations were consistent with prior analyses of katabatic wind patterns and were also related to the climatology of marine influences across the region. Finally, we contextualize the burn perimeter of the 2017 Thomas Fire, the largest fire in modern California history, relative to spatial patterns of katabatic and non-katabatic fires. The 2017 Thomas Fire began during the longest Santa Ana event in the last 70 years in an area that has been burned repeatedly by Santa Ana fires. However, the Thomas Fire ultimately burned into a region where there were no prior Santa Ana fires. The spatial delineation of two relatively distinct fire regimes is critical to making management decisions, such as where to locate suppression resources at critical times and where fuel treatments might be most effective. However, the anomalous pattern of the Thomas Fire also points to the potential for changes in anthropogenic and environmental factors to disrupt historical spatial patterns and suggests that spatial patterns of fire regimes are themselves prospective metrics of global change.

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Section: Fire Frequency and Patternsupporting

confidence: 67%

Spatial Distribution of Wildfires Ignited under Katabatic versus Non-Katabatic Winds in Mediterranean Southern California USA

Kolden

Abatzoglou

2018

Fire

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“…In summer, when fires are most frequent in California, large burned areas are promoted by the cumulative drying effects of atmospheric aridity and precipitation deficits mainly in forest ecosystems where fuel availability is not a limiting factor (Abatzoglou & Kolden, 2013;Jin et al, 2014;Keeley & Syphard, 2016;Swetnam, 1993;Swetnam & Betancourt, 1998;Westerling et al, 2003;Williams et al, 2018). In summer, when fires are most frequent in California, large burned areas are promoted by the cumulative drying effects of atmospheric aridity and precipitation deficits mainly in forest ecosystems where fuel availability is not a limiting factor (Abatzoglou & Kolden, 2013;Jin et al, 2014;Keeley & Syphard, 2016;Swetnam, 1993;Swetnam & Betancourt, 1998;Westerling et al, 2003;Williams et al, 2018).…”

Section: Introductionmentioning

confidence: 99%

Observed Impacts of Anthropogenic Climate Change on Wildfire in California

et al. 2019

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Recent fire seasons have fueled intense speculation regarding the effect of anthropogenic climate change on wildfire in western North America and especially in California. During 1972-2018, California experienced a fivefold increase in annual burned area, mainly due to more than an eightfold increase in summer forest-fire extent. Increased summer forest-fire area very likely occurred due to increased atmospheric aridity caused by warming. Since the early 1970s, warm-season days warmed by approximately 1.4°C as part of a centennial warming trend, significantly increasing the atmospheric vapor pressure deficit (VPD). These trends are consistent with anthropogenic trends simulated by climate models. The response of summer forest-fire area to VPD is exponential, meaning that warming has grown increasingly impactful. Robust interannual relationships between VPD and summer forest-fire area strongly suggest that nearly all of the increase in summer forest-fire area during 1972-2018 was driven by increased VPD. Climate change effects on summer wildfire were less evident in nonforested lands. In fall, wind events and delayed onset of winter precipitation are the dominant promoters of wildfire. While these variables did not change much over the past century, background warming and consequent fuel drying is increasingly enhancing the potential for large fall wildfires. Among the many processes important to California's diverse fire regimes, warming-driven fuel drying is the clearest link between anthropogenic climate change and increased California wildfire activity to date.Plain Language Summary Since the early 1970s, California's annual wildfire extent increased fivefold, punctuated by extremely large and destructive wildfires in 2017 and 2018. This trend was mainly due to an eightfold increase in summertime forest-fire area and was very likely driven by drying of fuels promoted by human-induced warming. Warming effects were also apparent in the fall by enhancing the odds that fuels are dry when strong fall wind events occur. The ability of dry fuels to promote large fires is nonlinear, which has allowed warming to become increasingly impactful. Human-caused warming has already significantly enhanced wildfire activity in California, particularly in the forests of the Sierra Nevada and North Coast, and will likely continue to do so in the coming decades.

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“…A wide range of processes can potentially alter observed anomalies during any individual event, and therefore, these episodes do not provide a definitive basis for attributing changes in the strength of ENSO or its teleconnections, a challenge that relates to both the evaluation of events in nature (e.g., Seager et al, ; Yeh et al, ) and models (Deser et al, ; Guilyardi et al, ). They do, however, raise questions regarding the role a warming climate may have had on both these and even more recent ENSO‐related extremes in California (Swain et al, ; Williams et al, , ; Yoon, Wang, Gillies, Hipps, et al, ) and other regions (Herrera & Ault, ; Wang, Huang, et al, ; Williams et al, ).…”

Section: Introductionmentioning

confidence: 99%

ENSO's Changing Influence on Temperature, Precipitation, and Wildfire in a Warming Climate

Fasullo

Otto‐Bliesner

Stevenson

2018

Geophysical Research Letters

134

115

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On interannual to decadal time scales, the climate mode with many of the strongest societal impacts is the El Niño–Southern Oscillation (ENSO). However, quantifying ENSO's changes in a warming climate remains a formidable challenge, due to both the noise arising from internal variability and the complexity of air‐sea feedbacks in the tropical Pacific Ocean. In this work, we use large (≥30‐member) ensembles of climate simulations to show that anthropogenic climate change can produce systematic increases in ENSO teleconnection strength over many land regions, driving increased interannual variability in regional temperature extremes and wildfire frequency. As the spatial character of this intensification exhibits strong land‐ocean contrasts, a causal role for land‐atmosphere feedbacks is suggested. The identified increase in variance occurs in multiple model ensembles, independent of changes in sea surface temperature variance. This suggests that in addition to changes in the overall likelihoods of heat and wildfire extremes, the variability in these events may also be a robust feature of future climate.

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Effect of Reduced Summer Cloud Shading on Evaporative Demand and Wildfire in Coastal Southern California

Cited by 26 publications

References 52 publications

Spatial Distribution of Wildfires Ignited under Katabatic versus Non-Katabatic Winds in Mediterranean Southern California USA

Spatial Distribution of Wildfires Ignited under Katabatic versus Non-Katabatic Winds in Mediterranean Southern California USA

Observed Impacts of Anthropogenic Climate Change on Wildfire in California

ENSO's Changing Influence on Temperature, Precipitation, and Wildfire in a Warming Climate

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