Coastal Santa Barbara (SB) County in Southern California, characterized by a Mediterranean climate and complex topography, is a region prone to downslope windstorms that create critical fire weather conditions and rapidly spread wildfires. The Santa Ynez Mountains, oriented from east to west, rise abruptly from the coast, separating air masses from the ocean and the Santa Ynez Valley. The juxtaposition of these geographic features generates spatiotemporally variable wind regimes. This study analyzes diurnal‐to‐seasonal wind cycles and extremes in this region using hourly data from eight weather stations and four buoys for the period 1998–2019. Data from a vertical wind profiler at the Santa Barbara airport in Goleta, CA was extracted from August 2016 to September 2020. Air temperature, dew point temperature, and the Fosberg fire weather index are examined at land stations. We show that cycles in wind speed vary spatiotemporally; mountain (valley and coastal) stations exhibit a pronounced semiannual (annual) cycle, and wind maxima is observed during the evening (afternoon) at mountain (valley and coastal) stations. Differences in wind speed percentiles were evident among stations, particularly at and above the 75th percentile. Strong winds recorded at buoys were significantly correlated (between
The increase in wildfire risk in the United States in recent decades has been linked to rapid growth of the wildland‐urban interface and to changing climate. While there have been numerous studies on wildfires and climate change, few have separately assessed the impact of climate response to land‐use‐land‐cover change (LULCC) on wildfires. In this study, we analyse two 10‐year regional climate simulations driven by the current (2011) and future (2100) land‐use‐land‐cover patterns to assess modifications by the projected LULCC to the frequency and severity of fire‐prone atmospheric conditions described by two fire weather indices, the Canadian Forest Fire Weather Index and the Hot‐Dry‐Windy Index. The simulation corresponding to future land‐use‐land‐cover pattern yields higher surface temperature and vapour pressure deficit and lower precipitation compared to the simulation with the current pattern in areas where urbanized landscapes replace forests and grasslands, such as along the Piedmont and outside the Chicagoland region, while in areas where croplands replace forests, such as the southeast Coastal Plains, the results are reversed. These changes to local and regional atmospheric conditions lead to longer fire seasons and more extreme fire‐weather conditions in much of the eastern United States, specifically in the Southeast and Ohio River Valley where significant urban expansion is projected by the end of the century. Whereas in Southern California where some highly flammable shrublands will be replaced by urban or crop lands, fire‐prone atmospheric conditions are likely to be less frequent and less extreme in the future. However, much of California moves towards a year‐round fire season under the projected LULCC. The results suggest that by altering atmospheric conditions, LULCC may play an important role in determining fire regime, but the effects are highly heterogeneous and regionalized.
more » « less- NSF-PAR ID:
- 10360916
- Publisher / Repository:
- Wiley Blackwell (John Wiley & Sons)
- Date Published:
- Journal Name:
- International Journal of Climatology
- Volume:
- 41
- Issue:
- 6
- ISSN:
- 0899-8418
- Page Range / eLocation ID:
- p. 3578-3597
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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Abstract r = 0.3–0.5) to land stations. However, cross‐correlational analysis did not reveal any temporal lags between mountain stations and buoys. Distributions of temperature and dew point during extreme winds differed between east and west mountain stations. Significant fire weather conditions were most frequent at mountain stations in Refugio and Montecito, with 5% occurrence in the spring and over 3% occurrence in fall. Weaker summertime winds lowered fire weather conditions at Montecito in the summer. -
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Abstract Earlier studies of land use land cover change (LULCC) normally used only a specified LULCC map with no interannual variations. In this study, using an Atmospheric General Circulation Model (AGCM) coupled with a land surface model, biophysical impacts of LULCC on global and regional climate are investigated by using a LULCC map which covers 63 years from 1948 to 2010 with interannual variation. A methodology has been developed to convert a recently developed LULCC fraction map with 1° × 1° resolution to the AGCM grid points in which only one dominant type is allowed. Comprehensive evaluations are conducted to ensure consistency of the trend of the original LULCC fraction change and the trend of the fraction of grid point changes over different regions. The model was integrated with a potential vegetation map (CTL) and the map with LULCC, in which a set of surface parameters such as leaf area index, albedo and other soil and vegetation parameters were accordingly changed with interannual variation. The results indicate that the interannual LULCC map simulation is able to reproduce better interannual variability of surface temperature and rainfall when compared to the control simulation. LULCC causes negative effect on global precipitation, with the strongest significant signals over degraded regions such as East Asia, West Africa and South America, and some of these changes are consistent with observed regional anomalies for certain time periods. LULCC causes reduction in net radiation and evapotranspiration which leads to changes in monsoon circulation and variation in magnitude and pattern of moisture flux convergence and subsequent reduction in precipitation. Meanwhile, LULCC enhances surface warming during the summer in the LULCC regions due to greatly reduced evapotranspiration. In contradiction to the surface, upper troposphere temperatures are cool because of less latent heat released into the upper troposphere, which leads to weaker circulation in LULCC regions.
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