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Over the past four decades, annual area burned has increased significantly in California and across the western USA. This trend reflects a confluence of intersecting factors that affect wildfire regimes. It is correlated with increasing temperatures and atmospheric vapour pressure deficit. Anthropogenic climate change is the driver behind much of this change, in addition to influencing other climate-related factors, such as compression of the winter wet season. These climatic trends and associated increases in fire activity are projected to continue into the future. Additionally, factors related to the suppression of the Indigenous use of fire, aggressive fire suppression and, in some cases, changes in logging practices...
Categories: Publication; Types: Citation
Natural climate variability can strongly temporarily enhance or obscure long-term trends in regional weather due to global climate change. We planned to explore (from our original proposal): (1) The influence of low frequency climate variability (interannual and decadal) on the seasonal probability distributions of daily weather (temperature and precipitation) within the Southwest, with a view on how natural variability modulates regional trends due to global warming. We explored natural climate variability and its impacts on extreme temperatures in Guirguis et al. (2015). We also explored natural climate variability and its impacts on precipitation extremes in Cavanaugh et al. (2015), Cavanugh and Gershunov (2015)...
Categories: Publication; Types: Citation
A new method for automatic detection of atmospheric rivers (ARs) is developed and applied to an atmospheric reanalysis, yielding an extensive catalog of ARs land-falling along the west coast of North America during 1948–2017. This catalog provides a large array of variables that can be used to examine AR cases and their climate-scale variability in exceptional detail. The new record of AR activity, as presented, validated and examined here, provides a perspective on the seasonal cycle and the interannual-interdecadal variability of AR activity affecting the hydroclimate of western North America. Importantly, AR intensity does not exactly follow the climatological pattern of AR frequency. Strong links to hydroclimate...
A new satellite-derived low cloud retrieval reveals rich spatial texture and coherent space-time propagation in summertime California coastal low cloudiness (CLC). Throughout the region, CLC is greatest during May–September but has considerable monthly variability within this summer season. On average, June is cloudiest along the coast of southern California and northern Baja, Mexico, while July is cloudiest along northern California's coast. Over the course of the summer, the core of peak CLC migrates northward along coastal California, reaching its northernmost extent in late July/early August, then recedes while weakening. The timing and movement of the CLC climatological structure is related to the summer evolution...
(Abstract from Geophysical Research Letters): Increasing wildfire and declining snowpacks in mountain regions threaten water availability. We combine satellite-based fire detections with snow seasonality classifications to examine fire activity in California's seasonal and ephemeral snow zones. We find a nearly tenfold increase in fire activity during 2020–2021 versus 2001–2019. Accumulation season broadband snow albedo declined 25%–71% at two burned sites (2021 and 2022) according to in-situ data relative to un-burned conditions, with greater declines associated with increased burn severity. By enhancing snowpack susceptibility to melt, both decreased snow albedo and canopy drove midwinter melt during a multi-week...
Categories: Publication; Types: Citation
Abstract (from Springer): Analyses of observed non-Gaussian daily minimum and maximum temperature probability distribution functions (PDFs) in the Southwest US highlight the importance of variance and warm tail length in determining future heat wave probability. Even if no PDF shape change occurs with climate change, locations with shorter warm tails and/or smaller variance will see a greater increase in heat wave probability, defined as exceedances above the historical 95th percentile threshold, than will long tailed/larger variance distributions. Projections from ten downscaled CMIP5 models show important geospatial differences in the amount of warming expected for a location. However, changes in heat wave probability...
(Abstract from Springer): The Sierra Nevada and Southern Cascades—California’s snowy mountains—are primary freshwater sources and natural reservoirs for the states of California and Nevada. These mountains receive precipitation overwhelmingly from wintertime storms including atmospheric rivers (ARs), much of it falling as snow at the higher elevations. Using a seven-decade record of daily observed temperature and precipitation as well as a snow reanalysis and downscaled climate projections, we documented historical and future changes in snow accumulation and snowlines. In four key subregions of California’s snowy mountains, we quantified the progressing contribution of ARs and non-AR storms to the evolving and projected...
Categories: Publication; Types: Citation
Abstract (from http://onlinelibrary.wiley.com/doi/10.1002/2015GL063238/pdf): The probability tail structure of over 22,000 weather stations globally is examined in order to identify the physically and mathematically consistent distribution type for modeling the probability of intense daily precipitation and extremes. Results indicate that when aggregating data annually, most locations are to be considered heavy tailed with statistical significance. When aggregating data by season, it becomes evident that the thickness of the probability tail is related to the variability in precipitation causing events and thus that the fundamental cause of precipitation volatility is weather diversity. These results have both theoretical...
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The Southwest Climate Adaptation Science Center supports conservation and management of the Southwest’s natural resources and cultural heritage by building partnerships between scientists and decision-makers, fostering development of research products to inform decisions, and assisting American Indian communities in adapting to climate change in the southwestern United States. Our vision it to help to maintain and sustain the Southwest’s unique biodiversity, its ecosystems’ diverse contributions to human welfare, and its diverse cultures, [both indigenous and adventitious,] as the region’s climate undergoes change in the coming years and decades. The SW CASC is hosted by the University of Arizona. Other consortium...
Abstract Low-level stratiform clouds modulate California's coastal climate during the warm season. Previous work describing the seasonal and daily variability of coastal low cloudiness (CLC) suggests that in July, August, and September southern California's CLC is under the influence of an additional driver, which has less impact in northern California. In this work, we introduce the link in which free-tropospheric moisture dictated by North American Monsoon (NAM) processes can impact southern California CLC. We use in situ and remote sensing observations, as well as reanalysis and single column model simulations to identify and investigate this previously missing component. We find that monsoonal moisture advected...
Categories: Publication; Types: Citation
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The Colorado River provides water to 40 million people in the southwestern United States. Consistent water level declines in Colorado River Basin reservoirs have focused research attention on the long-term changes in winter precipitation and the timing of snowmelt and runoff. Research on how warming temperatures affect winter precipitation and spring snowmelt is ongoing, however, less attention has been given to changes in spring and summer precipitation which also affects water supply, plant growth, and competition between native and non-native plants, and, in turn affects wildfire dynamics and wildlife habitat. The amount and timing of summer precipitation is largely influenced by variation in the North American...
    map background search result map search result map Southwest Climate Adaptation Science Center Consortium- Hosted by University of Arizona (2018-2023) Understanding the Effects of Seasonal Precipitation Changes on Hydrology and Ecosystems in the Colorado River Basin Understanding the Effects of Seasonal Precipitation Changes on Hydrology and Ecosystems in the Colorado River Basin Southwest Climate Adaptation Science Center Consortium- Hosted by University of Arizona (2018-2023)