Post-fire Temperature Research Articles

Experimental and numerical analysis on the post-fire flexural behavior of aluminum alloy gusset joints

Regarding the damage incurred by aluminum alloy latticed shells under fire loads, a crucial aspect in assessing structural integrity is examining the residual bearing capacity of aluminum alloy gusset (AAG) joints. Consequently, this paper conducted experimental and numerical analyses on the post-fire flexural behavior of AAG joints. Initially, twelve AAG joints underwent post-fire tests, revealing that the failure patterns differed between thin-plate joints (exhibiting block tearing of gusset plates) and thick-plate joints (exhibiting member buckling). Notably, the initial stiffness approximately remained constant, while a trilinear relationship emerged between the ultimate flexural bearing capacity and the maximum post-fire temperature. Subsequently, finite element (FE) analysis was carried out, and the accuracy of FE models was verified by comparing the FE results with the test results. A comprehensive parametric analysis, considering various plate thicknesses, post-fire temperatures, and aluminum alloy brands, was then conducted. Ultimately, employing statistical regression, theoretical equations were formulated to estimate both bending stiffness and bearing capacity for AAG joints after exposure to fire.

Post-fire response of S235 steel plates considering different bolt hole-making processes

PurposeThis study aims at investigating the effect of bolt hole-making processes on the post-fire behavior of S235 steel plates.Design/methodology/approachA total of nine steel plates with a single bolt hole are tested. The single bolt holes are fabricated using three different hole-making processes: drilling, waterjet and plasma. Among the nine steel plates, three fabricated specimens are control specimens and are tested at ambient temperature. The six remaining steel plates with a single bolt hole are subjected to a complete heating-cooling cycle and then monotonically loaded until failure. The six fabricated specimens are first heated up to two different temperatures 800 and 925 °C, and then cooled back to the ambient prior to loading.FindingsThe results show that after being exposed to post-fire temperatures (800 and 925 °C), the maximum decrease in strength of the S235 steel plate was 6% (at 925 °C), 14% (at 925 °C) and 22% (at 800 °C) when compared to the results of ambient specimens for waterjet, drilled and plasma bolt holes, respectively. For post-fire temperature tests, drilled and waterjet bolt hole-making processes result in having approximately the same load-displacement response, and both have larger strength and ductility than those obtained using plasma cutting.Originality/valueThis study provides preliminary data to guide the steel designers and fabricators in choosing the most suitable hole-making process for fire applications and to quantify the post-fire reduction in capacity of S235 plates.

Wildfire-induced shifts in groundwater discharge to streams identified with paired air and stream water temperature analyses

Within the western United States, increasingly severe and frequent wildfires may alter the magnitude, timing, and quality of water exported from burned areas by streams. Post-fire hydrologic studies often focus on peak stream flow responses to shifts in runoff generation or on annual streamflow yield response to changes in evapotranspiration following fire. However, the magnitude and duration of wildfire effects on groundwater recharge, changes in subsurface routing, and consequences for stream low flows sourced predominately by baseflow are poorly understood. Here, we demonstrate an approach using the amplitude and phase of paired annual air and stream water temperature signals to broadly identify changes in watershed subsurface flow contributions after fire. Watersheds were classified using pre-fire temperature data, as having air-coupled (i.e., reduced apparent groundwater signature), deep groundwater, or shallow groundwater stream temperature signals. Changes in pre- and post-fire paired air and stream water temperature metrics were compared for locations (n = 17) spanning a large range of physiographic and climatic conditions across the western United States. Pre- and post-fire comparisons were computed by quantile using bootstrapped confidence intervals (ci = 95), as well as in aggregate using Kruskal-Wallis and post-hoc Dunn tests. Statistical comparisons of pre- and post-fire temperature metrics suggest that overall, watersheds classified as having minimal groundwater influence are the most likely to experience fire-induced subsurface hydrologic change. More specifically, watersheds classified as having air-coupled or shallow groundwater signals experienced increases in the magnitude of groundwater discharge, with more stable annual thermal regimes post-fire that are less-coupled to ambient air temperature. These findings form the basis of a conceptual framework for watershed resistance to subsurface hydrologic change following fire that can be broadly applied as a first approximation for water management, impacts on aquatic habitat, and post-wildfire response planning.

Assessing Modern Calluna Heathland Fire Temperatures Using Raman Spectroscopy: Implications for Past Regimes and Geothermometry

Charcoal geothermometry continues to offer considerable potential in the study of palaeowildfires over decadal, centennial, millennial, and deep time scales—with substantial implications for the understanding of modern wildfire intensification. Recent developments in the application of Raman spectroscopy to carbonaceous organic material have indicated its capability to potentially reconstruct the palaeocharcoal formation temperature, and equivalent palaeowildfire pyrolysis intensity. Charcoal reflectance geothermometry (which also relies upon microstructural change with thermal maturation) has also been the subject of extensive modern evaluation, with multiple studies highlighting the key influence of energy flux on the resultant charcoal microstructure. The ability to accurately quantify modern wildfire temperatures based upon novel Raman-charcoal analyses has not yet been attempted. Using Raman band width-ratios (i.e., FWHMRa) and accompanying geothermometric trends to natural wildfire charcoals, our results identify differences between microstructurally-derived fire temperatures compared to those recorded during the fire event itself. Subsequent assessments of wildfire energy flux over time indicate no dominant influence for the observed differences, due to the inherent complexity of natural fire systems. Further analysis within this study, regarding the influence of reference pyrolysis methodology on microstructural change, also highlights the difficulty of creating accurate post-fire temperature reconstructions. The application of Raman spectroscopy, however, to the quantification of relative changes in fire temperature continues to prove effective and insightful.

Wildfire effects on mass and thermal tolerance of Hydropsyche oslari (Trichoptera) in southwestern USA montane grassland streams

Large-scale disturbances, such as wildfire, can markedly affect streams for years. As terrestrial areas within a watershed slowly recover, stream environments and biota can experience repeated and long-lasting challenges. In 2011, the Las Conchas wildfire burned 1/3 of the Valles Caldera National Preserve in northern New Mexico, USA. Seven y post-fire, streams located near the burn perimeter continue to experience varying levels of alteration (e.g., channel alteration with large diel temperature swings), whereas the terrestrial uplands have begun to recover. Extreme temperatures in stream systems may affect the aquatic community, including ectotherms such as caddisflies. These post-fire temperature ranges may increase an ectotherm’s breadth of thermal adaptation, but at metabolic costs that diminish organismal performance, such as growth, development, and fecundity. In this study we characterized in-situ effects of varied thermal regimes across preserve streams on the performance of the caddisfly Hydropsyche oslari Banks, 1905. We measured mass and critical thermal maximum (CTmax) in H. oslari larvae from preserve streams affected by wildfire (high temperature range) and in streams minimally affected by wildfire (low temperature range). We predicted that increased daily temperature maxima and reduced daily temperature minima (i.e., large diel temperature swings) would be associated with reduced H. oslari mass because of the limiting effects of suboptimal temperatures on growth. As predicted, in the weeks prior to their emergence as terrestrial adults, 5th-instar larvae within the high-temperature range stream had reduced mass (mean 3.3 ± SE 0.55 mg) relative to larvae from the low-temperature range stream (6.2 ± 0.69 mg). We also predicted that CTmax of H. oslari would reflect stream thermal history. Indeed, larvae H. oslari from the high-temperature range stream exhibited increased CTmax (35.4 ± 0.17°C) compared with larvae from the low-temperature range stream (34.4 ± 0.28°C). We demonstrated that the effects of wildfire on caddisflies can be long lasting, as evidenced by the reduced size at maturity and higher thermal tolerance in a caddisfly population 7 y post-fire.

Seed tolerance to post-fire temperature fluctuation of Cerrado legume shrubs with micromorphological implications

Multiple environmental cues may break seed physical dormancy (PY) in fire-prone ecosystems, but disentangling the roles of such cues remains challenging. Current research has mostly focused on the role of high temperatures (heat shocks) in PY alleviation, while post-fire environmental conditions are less understood. Here, we examined the role of post-fire temperature fluctuation on seed germination and viability of Cerrado legume shrubs. Specifically, we investigated (1) whether PY is broken by temperature fluctuation; (2) whether seed viability is affected by temperature fluctuations; and (3) micromorphological changes in the seed coat following exposure to temperature fluctuation. Seeds of nine legume species were collected in frequently burned Cerrado savannas. We simulated post-fire temperature fluctuation in germination chambers, with daily temperature fluctuation ranging from 18 to 55 °C for 90 days; controls consisted of untreated seeds (room temperature). We conducted germination trials with unblocked and blocked hilar region of seeds. In addition, seed samples were fixed and subjected to micromorphological analysis. Instead of dormancy break, three species showed decreased seed germination for both unblocked and blocked hilar regions, while other two species showed decreased germination in blocked seeds only. Nevertheless, random cracks formed across the seed coat were found in control and treated seeds, which displayed a proportion of nondormant seeds. Within nondormant seeds, both hilar and extra-hilar regions (such as the pleurogram) may take part on water uptake. Despite the lack of dormancy break, most Cerrado legume seeds persisted viable after post-fire temperature fluctuation, thus avoiding establishment under hazardous conditions. Seed tolerance to heat shocks and post-fire temperature fluctuation likely drives regeneration from seed in burned Cerrado areas.

Origins of abrupt change? Postfire subalpine conifer regeneration declines nonlinearly with warming and drying

AbstractRobust tree regeneration following high‐severity wildfire is key to the resilience of subalpine and boreal forests, and 21st century climate could initiate abrupt change in forests if postfire temperature and soil moisture become less suitable for tree seedling establishment. Using two widespread conifer species, lodgepole pine (Pinus contorta var. latifolia) and Douglas‐fir (Pseudotsuga menziesii var. glauca), we conducted complementary experiments to ask (1) How will projected early‐ to mid‐21st‐century warming and drying affect postfire tree seedling establishment and mortality? (2) How does early seedling growth differ between species and vary with warming and drying? With a four‐year in situ seed‐planting experiment and a one growing season controlled‐environment experiment, we explored effects of climate on tree seedling establishment, growth, and survival and identified nonlinear responses to temperature and soil moisture. In our field experiment, warmer and drier conditions, consistent with mid‐21st‐century projections, led to a 92% and 76% reduction in establishment of lodgepole pine and Douglas‐fir. Within three years, all seedlings that established under warmer conditions died, as might be expected at lower elevations and lower latitudes of species’ ranges. Seedling establishment and mortality also varied with aspect; approximately 1.7 times more seedlings established on mesic vs. xeric aspects, and fewer seedlings died. In the controlled‐environment experiment, soil temperatures were 2.0°–5.5°C cooler than the field experiment, and warming led to increased tree seedling establishment, as might be expected at upper treeline or higher latitudes. Lodgepole pine grew taller than Douglas‐fir and produced more needles with warming. Douglas‐fir grew longer roots relative to shoots, compared with lodgepole pine, particularly in dry soils. Differences in early growth between species may mediate climate change effects on competitive interactions, successional trajectories, and species distributions. This study demonstrates that climate following high‐severity fire exerts strong control over postfire tree regeneration in subalpine conifer forests. Climate change experiments, such as those reported here, hold great potential for identifying mechanisms that could underpin fundamental ecological change in 21st‐century ecosystems.

The Effect of Postfire Temperature Anomalies on Seasonal Soil Thawing in the Permafrost Zone of Central Siberia Evaluated Using Remote Data

This article contains data on the dynamics of thermal fields in postfire areas obtained using remote satellite imagery. It is found that postfire areas of the permafrost zone have a background thermal field in the range of 10.780–11.280 μm, which is caused by changes in the parameters of the stand, the ground cover, and the litter. The average surface temperature of postfire areas in larch forests is characterized by increasing up to ΔT = 7.2 ± 1.3°С relative to the control values in summer, which is 20–40% higher than the temperature of the control undisturbed areas. Temperature anomalies last for more than 10 years under conditions of the natural restoration of the ground cover. It is found that the rate of recovery of temperature anomalies is 2.5 times lower than the dynamics of the NDVI vegetative index. It is numerically evaluated that temperature anomalies on the soil surface could lead to an increase in the thawing depth of the soil layer by up to 20% more than the average statistical rate.

The Effect of Post-Fire Temperature Anomalies on Seasonal Thawing of Soils in the Permafrost Zone f Central Siberia Evaluated Using Remote Data

The Effect of Post-Fire Temperature Anomalies on Seasonal Thawing of Soils in the Permafrost Zone f Central Siberia Evaluated Using Remote Data

Effects of fire severity and post-fire climate on short-term vegetation recovery of mixed-conifer and red fir forests in the Sierra Nevada Mountains of California

Abstract Forest ecosystems in the Sierra Nevada Mountains of California are greatly influenced by wildfire as a natural disturbance, and increased fire severity and drought occurrence may alter the course of post-fire recovery in these ecosystems. We examined effects of fire severity, post-fire climate, and topographic factors on short-term ( 405 ha) between 1999 and 2006 were examined. According to the modeling results provided by ordinary least squares (OLS) regressions including spatial variation coefficients, fire severity, post-fire wet eason precipitation, post-fire January minimum temperature, and topographic factors explain variations in short-term post-fire NDVI values (adjusted R-squared = [0.680, 0.688] for red fir forests; adjusted R-squared = [0.671, 0.678] for mixed-conifer forests). The modeling results indicated that burned mixed-conifer forest was sensitive to post-fire drought, while burned red fir forest, with higher summer soil moisture availability, was sensitive to post-fire temperature. We also found that differences in recovery related to fire severity disappeared more quickly in burned mixed-conifer forest than in burned red fir forest. Future efforts should focus on long-term recovery, including competition between forest and shrub species in previously burned areas.

Simulated post-fire temperature affects germination of native and invasive grasses in cerrado (Brazilian savanna)

Background: Although fire is an important factor in determining cerrado vegetation, information about its effect on seed banks is sparse. Cerrado fires are rapidly moving surface fires with low residence time, producing only short-term heating of the uppermost centimetres of the soil. However, the reduction in vegetation cover and deposition of ashes increases the daily amplitude of soil temperature by as much as 35 °C.Aims: To assess the effect of post-fire daily soil temperatures on the germination of one alien and nine native grasses.Methods: Seeds were stored at alternating temperatures of 45 ºC/10 ºC (10 h/14 h) for 7 d or 30 d, simulating two different storage times in the soil seed bank before the onset of the rainy season. Germination was monitored over 30 d.Results: The variation in temperature had a significant effect on the rate of seed germination in some species, either enhancing it (Aristida setifolia) or reducing it (Schizachyrium sanguineum). Increased storage time reduced the viability of S. sanguineum and Echinolaena inflexa. The invasive Melinis minutiflora had the highest germination rate and it also showed the best toleration of post-fire conditions (45 ºC/10 ºC) after 7 d, with significant reduction in the germination time after 30 d.Conclusions: Fire seems to have a significant effect in the early life of cerrado grasses. Some native species responded positively to temperature oscillation, suggesting that they should be better prepared to compete with alien species after a fire, with more of their seeds germinating and/or at a more rapid rate.