Spatially-explicit information on canopy fuel parameters is key for wildfire propagation modelling, emission estimations and risk assessment. This work aims to develop easily-replicable methods to estimate critical fuel canopy parameters from spaceborne LiDAR observations acquired by the Global Ecosystem Dynamics Investigation (GEDI) sensor onboard the International Space Station. GEDI-like pseudowaveforms were modelled from discrete Airborne Laser Scanning (ALS) data and used to select the best GEDI predictor metrics to derive European wall-to-wall forest height and canopy cover maps. Then, GEDI spaceborne footprints were used to generate continental maps of canopy parameters through a two-steps approach: 1) Spatial interpolation of GEDI footprints inside homogeneous forest fuel type polygons, and 2) Modelling machine learning algorithms for the forest fuel type polygons without GEDI footprints inside, using auxiliary multispectral and RADAR imagery and biophysical variables. Our results show the capabilities of remote sensing and GEDI to estimate and map the spatial patterns of critical forest canopy fuel parameters in fire risk prevention and contribute to generating the necessary tools to develop an integrated risk-wise strategy that reduces fire vulnerability of ecosystems across Europe.

How to cite: Aragoneses, E., García, M., and Chuvieco, E.: Estimating and mapping forest canopy fuel parameters from GEDI LiDAR data in Europe, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-2268, https://doi.org/10.5194/egusphere-egu23-2268, 2023.

Changing climate is likely to increase the intensity of forest fires in Austria. Consequently, the investigation of the fire danger situation at the wildland-urban interface is crucial for the planning of prevention measures against future damages. Hence, a comprehensive fire risk assessment study was performed for Austria, in which five components were considered (natural cause for ignition of forest fires, socioeconomic causes for ignition, vegetation structure, meteorological factors and exposition of important infrastructures). The approach for the fire danger assessment determined for the city of Graz, the second largest city in Austria, as high danger level for fire occurrences. Therefore, the present work introduces a case study for this city, focusing on the exposure of settlements and infrastructure to fire events. The relevant infrastructure features were selected, such as residential buildings, power lines, radio stations, railways, highways and traffic and communication buildings, as well as three types of forests with different management objectives (production forest, site protection forest and object protection forest). In order to analyze the interaction between settlements and vegetation in case of forest fires, buffers were used (i.e. buffer sizes for buildings are 10m, 50m and 150m and other settlements are 60m, 100m and 200m). Infrastructure and forest cover were also classified due to their importance: high, medium and low risk of exposition. For example, production forest was considered to bear a lower risk of exposition due to their economic importance compared to protection forests, that have to protect the city from natural hazards like rock falls or mudflows. On the other hand, radio stations carry a high risk of exposition because of their importance for facilitating the communication of the community. In combing the results of the fire danger assessment for the city of Graz with final exposition map the results indicate that areas around radio stations situated in the northwestern area of the city have a higher risk of exposition. As a result, firefighters must pay particular attention to this region for management and evacuation plans.

How to cite: Silva Andrade, M., M. Müller, M., Dioszegi, G., and Vacik, H.: Exploring the fire danger and exposition of settlements at the wildland urban interface: a case study in Graz, Austria, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-13012, https://doi.org/10.5194/egusphere-egu23-13012, 2023.

Intensifying wildfires in high-latitude forest and tundra ecosystems are a major source of greenhouse gas emissions, releasing carbon through direct combustion and long-term degradation of permafrost soils and peatlands. Several remotely sensed burned area and active fire products have been developed, yet these do not provide information about the ignitions, growth and size of individual fires. Such object-based fire data is urgently needed to disentangle different anthropogenic and bioclimatic drivers of fire ignition, spread and extinction.

We developed an object-based fire tracking method to map the evolution of fires at a sub-daily scale using Visible Infrared Imaging Radiometer Suite (VIIRS) active fire detections. The dataset includes ignitions and sub-daily perimeters of individual fires between 2012 and 2021, which are corrected using finer-scale information on waterbodies. Here, we present first results of this circumpolar arctic-boreal fire atlas. We show circumpolar patterns of arctic-boreal fire activity and disentangle the spatially varying influence of drivers of fires. Most fires, as well as the largest fires, occur on the Eurasian continent. Latitudinal differences in fire characteristics and drivers are important, yet regional and continental differences emerge. Knowledge about regional differences in fire regimes and their drivers is required to better understand contemporary arctic-boreal fire regimes and to constrain models that predict changes in future arctic-boreal fire regimes.

How to cite: Scholten, R., Chen, Y., Veraverbeke, S., and Randerson, J.: Circumpolar patterns of arctic-boreal fire activity, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-16785, https://doi.org/10.5194/egusphere-egu23-16785, 2023.

Forest fires and extreme droughts will continue to be main disturbances in Mediterranean ecosystems, given the ongoing and projected climatic changes. In fact, an exacerbation of some aspects of their regime is expected. In this perspective, it is fundamental to design adaptive management strategies that can reduce the impact of disturbances and increase ecosystem resilience. To achieve this, it is necessary to develop an integrated management, able to select the best combination of restoration actions for different scenarios. Here, we address the effectiveness of the combination of several actions related to fuel reduction and restoration after fire in the long term, to increase the presence of resprouting species and mitigate fire occurrence, for different future climate change scenarios. Fuel reduction treatments include the application of shrub clearing at different intensities and frequencies. Restoration actions comprise the plantation of resprouting species, aiming to increase ecosystem resilience. We used a simple, ecological, published model, specifically developed for Mediterranean ecosystems and including species competition and post-fire responses, which we calibrated using the recorded vegetation response to treatments. Our results point out that, if we look for more resilient ecosystems in the next decades, we will need an intensification of fuel reduction treatments. Noticeably, including resprouting species has an important effect in the ecosystem. However, the success of these actions will be variable depending on the climate scenario.

How to cite: Baudena, M., Vallejo, V. R., Baeza, J., Moghli, A., Valdecantos, A., and Santana, V. M.: Long-term management actions of fire-prone Mediterranean ecosystems under climate change using fuel reduction and post-fire restoration, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-9283, https://doi.org/10.5194/egusphere-egu23-9283, 2023.

Fire is a major factor shaping plant communities, and plant species have evolved to persist through a fire regime, broadly characterised by the frequency, intensity, and season of burns typical of their region. However, historical fire regimes are shifting with changing climate and other factors, including increased ignition sources, and implemented fires, producing more frequent burns of varying intensity. As such, seasonality of fire is shifting and despite the effects of fire on plant persistence being well studied, there is still little understanding on the effects of fire season. In this study, we set up two sites with five treatment areas, an early autumn burn, late autumn burn, early spring burn, late spring burn and a control. We surveyed multiple shrub species for impacts of seasonal burns on resprouting vigour and post-fire flowering in the mediterranean region of South Australia. Fire severity was also measured using soil temperatures, canopy cover consumption and minimum twig diameter. We found that fire response to fire season varied between trait type included seed storage type and seed dormancy type. This study highlights the impact of season of fire and that it should be considered when making species management decisions for plant species persistence.

How to cite: Thomsen, A. and Ooi, M.: Shifting fire season: who has it worse resprouters, or obligate seeders?, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-10798, https://doi.org/10.5194/egusphere-egu23-10798, 2023.

In New Caledonia, a significant fraction of soils developed on the Peridotite Nappe are naturally enriched in trace metals, such as nickel and chromium, that can be remobilized upon wildfires (Thery et al., 2022). In this Pacific archipelago, the average annual burnt vegetation surface is estimated to be 30,000 ha, representing 2% of the total land surface (Dumas et al., 2013). However, much larger surfaces can burn during strong El Nino years. This was notably the case in 2016 at Ile des Pins, in the South part of the archipelago, where the burnt surface reached 1000 ha compared to an average annual value of 300 ha. Concomitantly, a dramatic increase in nickel concentrations could be observed in some water supply catchments, with some values reaching up to 4000 µg/L compared to the WHO and European guidelines of 70 µg/L and 20 µg/L, respectively. This situation led the authorities to order some investigations to better understand the link between these increased wildfires and the degradation of freshwater quality.

In this presentation, we will discuss the results of these investigations performed for two years on the dynamics and biogeochemistry of nickel across a drinking water catchment supplied by both surface and groundwater. The surface water originates from a doline, which is a characteristic feature of karstic landscapes frequently observed in the lateritic landscapes on ultramafic rocks from New Caledonia (Jeanpert et al., 2016). Geochemical analyses of the surface water collected in the burnt doline showed very high nickel concentration (i.e. up to 300,000 µg/L) compared to groundwaters (i.e below 30 µg/L). These surface waters were also found enriched in sulfate (i.e. up to 3200 mg/L) compared to groundwaters (i.e. below 8 mg/L). Water isotopes analyses allowed to propose a simple mixing model between these two end-members to reconstitute the water supply at the drinking water catchment. In addition, mineralogical characterization of the doline sediments and XAS-derived analysis of nickel speciation allowed to evidence a mixed Mg/Ni-sulfate and Ni/Fe-sulfides as the two major Ni-bearing mineral species. Although the sulfides are common species in sedimentary settings, the occurrence of a mixed Mg/Ni sulfate was considered to result from the large 2016 wildfires that impacted the nickel biogeochemistry in the sediments. The high solubility of this latter mineral species is probably playing a major control on nickel concentration in the water that is supplied to the downstream drinking water catchment.

This study brings further understanding on how wildfires can impact drinking water catchments quality by modifying the biogeochemical cycling of trace metals across their related watersheds. In the case of New Caledonia where most of drinking water catchments are supplied by surface water (a significant fraction of them being related to ultramafic watersheds), it spreads awareness to local policy-makers about the vulnerability of the water resource relative to wildfires. At a larger scale, it also put some warning on the possible impact of wildfires on drinking water catchments related to ultramafic watersheds worldwide.

How to cite: Thery, G., Juillot, F., Jeanpert, J., Calmels, D., Morin, G., Montarges-Pelletier, E., Bourbon, E., Kieffer, I., Genthon, P., and Quantin, C.: How wildfires can impact nickel concentration and biogeochemistry at ultramafic drinking water catchments: An example study in New Caledonia, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-4580, https://doi.org/10.5194/egusphere-egu23-4580, 2023.

Wildfires are recognized as one of the most affecting ecological agents, altering geomorphological processes, hydrologic cycles, and water quality. On average from 50,000 to 65,000 fires occur in Europe every year, burning approximately 500,000 ha of forested areas. Between September 2018 and February 2019 two large wildfires burnt nearly 1,400 ha of forests and farmlands in the Pisano Mount area (northwestern Tuscany). The mountainous morphology of the area linked to the proximity to the sea causes high precipitation variability and intensity. This, joined with low permeability bedrock (mainly quartzites, schists, and phyllites) and with the extensive vegetation coverage, make the study site a hot spot for surface waters analysis. Moreover, burnt catchments are of primary importance in the recharge processes of the groundwater resources of the costal plain, which are exploited by a large number of inhabitants and agricultural facility. Consequently, the present study is aimed at understanding and quantifying the wildfire impacts on the hydrogeological dynamics and water quality in the studied catchments. Such impacts are being evaluated by comparing burnt and unburnt catchments, which were selected to be as similar as possible from geological, morphological, and vegetational perspectives. The multi-parameter selection method involved Principal Component Analysis and Distance analysis on many potentially feasible catchments. A network of automatic monitoring instruments was deployed on site. Five hydraulic sections of the main streams draining the area were monitored for hydraulic level and physico-chemical parameters. Hydrographs analysis was performed to infer differences in hydrogeological dynamics between burnt and unburnt basins. Monthly samples were collected for stream water and groundwater chemical analysis. In addition, four plate lysimeters were installed to sample soil water for its chemical characterization. The chemical analysis involved major anions and cations, trace elements, water isotopes, and organic compounds, to search for chemical perturbation potentially arising from the wildfire. The investigation highlighted various differences between the burnt and unburnt basin, mainly for the surface waters. The streams draining the burnt areas present different hydraulic behaviour and changes in physiochemical parameters in response to rainfall events. Moreover, the yearly variation of physiochemical parameters and chemical characteristics present an higher variance for those streams draining wildfire affected catchments.

How to cite: Nigro, M., Giannecchini, R., Doveri, M., Menichini, M., and Baneschi, I.: Mediterranean catchments post-fire hydrogeological behavior and water quality: insights from the Pisano Mount area (Tuscany, Italy), EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-14379, https://doi.org/10.5194/egusphere-egu23-14379, 2023.

Wildfires play the role of ecosystem shapers in the majority of terrestrial biomes. Nowadays, their regimes are changing as a consequence of land abandonment and climate change. After-fire dynamics are widely studied in North America and Mediterranean environments. However, soils developed in different biomes might not unequivocally respond to fire-induced heating, and forests of the Western Italian Alps are not unfamiliar to fire occurrence.

For these reasons, we conducted several experiments (at plot and lab scale) at environmentally realistic conditions to systematically assess the impacts of fire on the physico-chemical properties of soils belonging to the Italian Alpine ecological region.

A homogenous pine forest (Pinus sylvestris L.) located in a mountain region near Torino experienced the passage of a severe and large wildfire in fall 2017. The field survey carried out in 2020 revealed that lower organic carbon (OC) contents and higher bulk density (BD) values were associated to a greater fire severity. Abundance of pyrogenic carbon was related to the steepness degree, as a consequence of erosion. In the superficial horizons, the naturally high WR expected from soils developed under a conifer stand was not present.

To elucidate mechanisms regulating WR occurrence and evolution, the thermal transformations borne by Alpine soils were investigated at controlled laboratory conditions. Topsoil samples displayed extremely different wettable behaviors upon increasing temperatures (Ts), with or without WR build-up. This occurred mainly in relation to content and composition of organic matter (OM), particle size distribution and abundance of iron (Fe) oxides. Notwithstanding the initial sample hydrophobicity, WR was dramatically lost above 200 °C due to increasing pH values, inducing OM de-sorption from the negatively charged mineral surfaces.

In the same T range, the thermal transformation of soil Fe oxides were found to be primarily directed towards oxidative processes (hematite formation). Ts up to 300 °C could have potentially promoted the stabilization of the remaining (non-combusted) OM, with the synthesis of defect-rich Fe oxides and enrichment in condensed and aromatic compounds, and yet OM was highly dispersible at the high pH values resulting from the thermal treatment, such that OC might be weakly retained on mineral phases in an after-fire scenario.

How to cite: Negri, S., Giannetta, B., Mantero, G., Stanchi, S., Marzano, R., Garbarino, M., Celi, L., and Bonifacio, E.: Heating response patterns of Alpine soils: from a plot-scale to lab experiments., EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-13669, https://doi.org/10.5194/egusphere-egu23-13669, 2023.