Progressive forest canopy water loss during the 2012–2015 California drought

Asner, Gregory P.; Brodrick, Philip G.; Anderson, Christopher B.; Vaughn, Nicholas R.; Knapp, David; Martin, Robert E.

doi:10.1073/pnas.1523397113

Cited by 322 publications

(300 citation statements)

References 29 publications

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“…The factors catalysing mortality in these forests are the subject of intensive current research and include physiological stress from increasingly hot droughts and secondary effects such as increased beetle outbreaks and fire frequency or intensity (e.g. Allen et al 2015;Anderegg et al 2015;Moritz et al 2014;Mann et al 2016;Asner et al 2016). This paper adds spatial predictions of the forested areas most likely to experience climatic stress to the context, which represents in situ risk.…”

Section: Discussionmentioning

confidence: 99%

“…This approach portrays a rate of climate change that could directly impact dominant vegetation but does not account for annual variability or large-scale disturbances that may serve as tipping points for vegetation transition from one type to another, such as wildfire or severe drought (e.g. Allen and Breshears 1998;Breshears et al 2005;Asner et al 2016). While we do not predict the likelihood of one climate future over another, we assert that even if there is greater precipitation in the future, plant stress is likely to become higher due to increasing temperatures .…”

Section: Discussionmentioning

confidence: 99%

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Climate change vulnerability assessment of forests in the Southwest USA

et al. 2017

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Climate change effects are already apparent in some Southwestern US forests and are expected to intensify in the coming decades, via direct (temperature, precipitation) and indirect (fire, pests, pathogens) stressors. We grouped Southwestern forests into ten major types to assess their climate exposure by 2070 using two global climate models (GCMs) and two emission scenarios representing wetter or drier conditions and current or lowered emission levels. We estimate future climate exposure over forests covering 370,144 km 2 as the location and proportion of each type projected to experience climate conditions that fall outside 99% of those they currently occupy. By late century, 27-77% is climatically exposed under wetter or drier current emission levels, while lowered emission levels produce 10-50% exposure, respectively. This difference points to the benefits of reducing emissions from the RCP8.5 to the RCP4.5 track, with regard to forest retention. Exposed areas common to all four climate futures include central Arizona and the western slope of the Sierra Nevada. Vulnerability assessments also comprise sensitivity and adaptive capacity, which we scored subjectively by forest type according to the number of key stressors they are sensitive to and the resilience conferred by life history traits of their dominant tree species. Under the 2070 RCP8.5Climatic Change

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Section: Discussionmentioning

confidence: 99%

Section: Discussionmentioning

confidence: 99%

Climate change vulnerability assessment of forests in the Southwest USA

et al. 2017

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“…Caspar NDVI values are near the saturation limit of approximately 0.90 [52], which may be limiting the ability to detect vegetation changes and likely contributes to the extremely low standard deviation. The lowest NDVI and EVI values for mixed rain and snow Providence and snow-dominated Bull occur during 2014-2016, coinciding with drought-related canopy water loss [53] and tree mortality [46]. In contrast, the lowest NDVI value for Caspar occurs in 2004, while the lowest EVI value occurs in 2016, which may reflect the lower sensitivity of NDVI and the higher sensitivity of EVI in regions of high biomass [52].…”

Section: Vegetation Indicesmentioning

confidence: 98%

Recent Patterns in Climate, Vegetation, and Forest Water Use in California Montane Watersheds

Saksa

Safeeq

Dymond

2017

Forests

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California has recently experienced one of the worst droughts on record, negatively impacting forest ecosystems across the state. As a major source of the region's water supply, it is important to evaluate the vegetation and water balance response of these montane forested watersheds to climate variability across the range of rain-to snow-dominated precipitation regimes. The Standardized Precipitation Index (SPI) and the Standardized Runoff Index (SRI) were used to capture the hydrologic drought signal, and MODIS vegetation indices (i.e., the normalized difference vegetation index and the enhanced vegetation index) were used to evaluate the vegetation and evapotranspiration response in three headwater catchments. The study catchments comprised a low elevation rain-dominated site (Caspar Creek) on the northern California coast, a mid-elevation site with a mix of rain and snow (Providence Creek) in the California Sierra Nevada, and a high elevation snow-dominated site (Bull Creek) in the Sierra Nevada. Lowest SPI values occurred in the third drought year of 2014 for all sites. Lowest SRI was in 2014 for Caspar, but in 2015 for Providence and Bull, reflecting differences in snowpack-delayed runoff and subsurface storage capacity between the lower and higher elevation watersheds. The most accurate water balance closure using evapotranspiration estimates from vegetation indices was within 10% of measured precipitation at snow-dominated Bull. The rain-dominated Caspar watershed had the highest vegetation index values and annual evapotranspiration, with the lowest variability over the previous 13 years (2004-2016). Vegetation index values and annual evapotranspiration decreased with increasing elevation and snow contribution to precipitation. Both snow-influenced Sierra Nevada watersheds showed elevated vegetation and evapotranspiration responses to interannual climate variability. There remains a need for institutional support to expand long-term observations in remote forested mountain watersheds to monitor and research these changing and extreme environmental conditions in source watershed regions.

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“…Prior to water year [49], due to chronic below normal precipitation and exceptionally high rates of potential evapotranspiration associated with the warmest years in the observational record [50]. This chronic drought resulted in large scale loss of tree canopy water [51] and tree mortality across the Sierra Nevada. By contrast, the 2017 water year delivered well above normal to record precipitation across much of the state, with parts of the central to northern Sierra Nevada, and scattered locations near the San Francisco Bay Area receiving the most October-April precipitation since 1895 (Figure 5a).…”

Section: Climatic Basismentioning

confidence: 99%

The 2017 North Bay and Southern California Fires: A Case Study

Nauslar

Abatzoglou

Marsh³

2018

Fire

140

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Two extreme wind-driven wildfire events impacted California in late 2017, leading to 46 fatalities and thousands of structures lost. This study characterizes the meteorological and climatological factors that drove and enabled these wildfire events and quantifies their rarity over the observational record. Both events featured key fire-weather metrics that were unprecedented in the observational record that followed a sequence of climatic conditions that enhanced fine fuel abundance and fuel availability. The North Bay fires of October 2017 occurred coincident with strong downslope winds, with a majority of burned area occurring within the first 12 h of ignition. By contrast, the southern California fires of December 2017 occurred during the longest Santa Ana wind event on record, resulting in the largest wildfire in California's modern history. Both fire events occurred following an exceptionally wet winter that was preceded by a severe four-year drought. Fuels were further preconditioned by the warmest summer and autumn on record in northern and southern California, respectively. Finally, delayed onset of autumn precipitation allowed for critically low dead fuel moistures leading up to the wind events. Fire weather conditions were well forecast several days prior to the fire. However, the rarity of fire-weather conditions that occurred near populated regions, along with other societal factors such as limited evacuation protocols and limited wildfire preparedness in communities outside of the traditional wildland urban interface were key contributors to the widespread wildfire impacts.

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Progressive forest canopy water loss during the 2012–2015 California drought

Cited by 322 publications

References 29 publications

Climate change vulnerability assessment of forests in the Southwest USA

Climate change vulnerability assessment of forests in the Southwest USA

Recent Patterns in Climate, Vegetation, and Forest Water Use in California Montane Watersheds

The 2017 North Bay and Southern California Fires: A Case Study

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