234 research outputs found
Water waves generated by moving atmospheric pressure: Theoretical analyses with applications to the 2022 Tonga event
Both 1DH (dispersive and non-dispersive) and 2DH axisymmetric (approximate,
non-dispersive) analytical solutions are derived for water waves generated by
moving atmospheric pressures. In 1DH, three wave components can be identified:
the locked wave propagating with the speed of the atmospheric pressure, ,
and two free wave components propagating in opposite directions with the
respective wave celerity, according to the linear frequency dispersion
relationship. Under the supercritical condition (, which is the
fastest celerity of the water wave) the leading water wave is the locked wave
and has the same sign (i.e., phase) as the atmospheric pressure, while the
trailing free wave has the opposite sign. Under the subcritical condition () the fastest moving free wave component leads and its free surface
elevation has the same sign as the atmospheric pressure. For a long atmospheric
pressure disturbance, the induced free surface profile mimics that of the
atmospheric pressure. The 2DH problem involves an axisymmetric atmospheric
pressure decaying in the radial direction as . Only two wave
components, locked and free, appear due to symmetry.
The tsunami DART data captured during Tonga's volcanic eruption event is
analyzed. Corrections are necessary to isolate the free surface elevation data.
Comparisons between the corrected DART data and the analytical solutions,
including the arrival times of the leading locked waves and the trailing free
waves, and the amplitude ratios, are in agreement in order-of-magnitude. The
differences between them highlight the complexity of problems
Wildfires and geochemical change in a subalpine forest over the past six millennia
Citation: Bérangère Leys and Philip E Higuera and Kendra K McLauchlan and Paul V Dunnette. (2016). Wildfires and geochemical change in a subalpine forest over the past six millennia. Environmental Research Letters, 11(12), 125003.Bérangère Leys and Philip E Higuera and Kendra K McLauchlan and Paul V Dunnette. (2016). Wildfires and geochemical change in a subalpine forest over the past six millennia. Environmental Research Letters, 11(12), 125003.The frequency of large wildfires in western North America has been increasing in recent decades, yet the geochemical impacts of these events are poorly understood. The multidecadal timescales of both disturbance-regime variability and ecosystem responses make it challenging to study the effects of fire on terrestrial nutrient cycling. Nonetheless, disturbance-mediated changes in nutrient concentrations could ultimately limit forest productivity over centennial to millennial time scales. Here, we use a novel approach that combines quantitative elemental analysis of lake sediments using x-ray fluorescence to assess the geochemical impacts of high-severity fires in a 6200 year long sedimentary record from a small subalpine lake in Rocky Mountain National Park, Colorado, USA. Immediately after 17 high-severity fires, the sedimentary concentrations of five elements increased (Ti, Ca, K, Al, and P), but returned to pre-fire levels within three decades. Multivariate analyses indicate that erosion of weathered mineral material from the catchment is a primary mechanism though which high-severity fires impact element cycling. A longer-term trend in sediment geochemistry was also identified over millennial time scales. This decrease in the concentrations of six elements (Al, Si, K, Ti, Mn, and Fe) over the past 6200 years may have been due to a decreased rate of high-severity fires, long-term ecosystem development, or changes in precipitation regime. Our results indicate that high-severity fire events can determine elemental concentrations in subalpine forests. The degree of variability in geochemical response across time scales suggests that shifting rates of high-severity burning can cause significant changes in key rock-derived nutrients. To our knowledge, these results are the first to reveal repeated loss of rock-derived nutrients from the terrestrial ecosystem due to high-severity fires. Understanding the future of fire-prone coniferous forests requires further documentation and quantification of this important mechanism linking fire regimes and biogeochemical cycles
Social Vulnerability of the People Exposed to Wildfires in U.S. West Coast States
Understanding of the vulnerability of populations exposed to wildfires is limited. We used an index from the U.S. Centers for Disease Control and Prevention to assess the social vulnerability of populations exposed to wildfire from 2000–2021 in California, Oregon, and Washington, which accounted for 90% of exposures in the western United States. The number of people exposed to fire from 2000–2010 to 2011–2021 increased substantially, with the largest increase, nearly 250%, for people with high social vulnerability. In Oregon and Washington, a higher percentage of exposed people were highly vulnerable (\u3e40%) than in California (~8%). Increased social vulnerability of populations in burned areas was the primary contributor to increased exposure of the highly vulnerable in California, whereas encroachment of wildfires on vulnerable populations was the primary contributor in Oregon and Washington. Our results emphasize the importance of integrating the vulnerability of at-risk populations in wildfire mitigation and adaptation plans
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