SSS9.8

Wildfires around the world continue to increase in size, severity, and cost. Major concerns after wildfires include the increased runoff and erosion due to loss of the protective forest floor layer, loss of water storage, and creation of water repellent soil conditions. Salvage logging is often a post-fire forest management action to recoup the economic loss of the burned timber, yet concerns arise due to the impacts of this activity on erosion and downstream sedimentation. A decade of research dedicated to impacts of post wildfire salvage logging throughout the Western US has been conducted using rill experiments, paired swales, and remote sensing imagery. Using 2-m resolution WorldView imagery, we are now able to map logging equipment tracks spatially and ground-truth the imagery with field measurements. The Normal Difference Vegetation Index (NDVI) of the 2-m resolution WorldView imagery has allowed us to detect disturbed bare soil from the logging equipment tracks and can differentiate when wood slash was added to the track. Adding wood slash increased ground cover significantly which resulted in an order of magnitude decrease in hillslope erosion with the rill experiment and was confirmed with hillslope plots under natural rainfall as well. Riparian buffers are often managed for timber harvest disturbances to decrease the risk of hillslope erosion entering stream channels during runoff events. However, after wildfires, burned riparian buffers may become less efficient at infiltrating runoff and trapping and reducing soil loss. We investigated the efficiency of burnt over riparian buffers with a sediment-laden runoff experiment to determine how much infiltration occurs and how much sediment is removed by the buffer. Rill travel length significantly decreased through the buffer as vegetation regrowth provided increasing ground cover. In the high burn severity areas, sediment concentrations were 19 g/L immediately after the wildfire and reduced to 7–14 g/L after 10 months due to abundant vegetation recovery. The amount of sediment dropping out of the flow consistently increased over the study period and varied by burn severity. The sediment removal rate in the low burn severity area of 1.2 g/L/m approached the removal rate in the unburned buffer of 1.3 g/L/m after 2 years post-fire. Forest managers may need to increase the widths of burned stream buffers 2x to 8x during post-wildfire salvage logging operations to minimize sediment delivery to streams. Integrating erosion mitigation strategies into salvage logging operations should be commonplace when hillslope erosion and downstream sedimentation is a concern.

How to cite: Robichaud, P.: Post Wildfire Forest Management: Can We Reduce the Impact of Salvage Logging on Erosion and Stream Sedimentation?, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-10185, https://doi.org/10.5194/egusphere-egu22-10185, 2022.

The METEO unit of the National Observatory of Athens has developed and applies a set of operational services that employ state-of-the-art observational and modeling techniques with the aim to assist both the citizens and the authorities in better preventing, addressing, and ultimately mitigating the adverse impacts of forest fires. The early warning system platform, which has been initially developed in the frame of DISARM project, had been upgraded with improved functionalities in the frame of the CLIMPACT project, a flagship initiative on climate change to coordinate a Pan-Hellenic network of institutions.

The presentation focuses on the description of the system that encompasses the following pillars:

(a) Forecasting of forest fire danger: four widely used indices (Canadian Fire Weather Index - CFWI, Modified Nesterov, Fosberg and Haines) are operationally calculated for the next 3 days at 6kmx6km and 2kmx2km spatial resolution based on 3 state-of-the-art numerical weather prediction models (WRF, Bolam, Moloch). Especially for CFWI the fire danger thresholds have been adapted to the fire environment of Greece;

(b) Real time monitoring of the fire weather conditions: The monitoring is based on the online network of meteorological stations operated by the METEO Unit of NOA that includes ~450 stations across Greece. Fire weather monitoring also includes the daily estimation of landscape flammability using as a proxy the dead fuel moisture content (DFMC). DFMC is calculated using a physically based fuel moisture model and weather station data.

(c) IRIS a rapid response system for fire spread forecasting:  WRF-ARW NWP model and FIRE two-dimensional fire spread model are applied, along with a prototype high-resolution geospatial dataset for the representation of fuels, in a fully-coupled mode in order to account for the two-way interaction between fire and the atmosphere . Major upgrades of the IRIS system achieved in the frame of CLIMPACT include the online calculation of dead fuel moisture, the increase of spatial resolution (40mx40m pixels) of the prototype fuel model for Greece, and the delivery of a forecast guidancewhich includes the categorization (using a 7-level scale) of forest fires based on the forecasted behavioral characteristics.

How to cite: Kotroni, V., Giannaros, T., Dragozi, E., Lagouvardos, K., Bezes, A., and Koletsis, I.: Early warning system for forest fires in Greece: developments and upgrades in the frame of Climpact project, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-4443, https://doi.org/10.5194/egusphere-egu22-4443, 2022.

This work focuses on the extreme pyroconvective wildfires that impacted southern Greece in early August 2021. These wildfires were unprecedented in extent, intensity, and impacts. They broke out in Attica, Euboea, Elis, Messenia, and Laconia, on August 03 and 04, 2021, and kept burning for several days. Observational evidence indicates that all wildfires exhibited extreme fire behavior, characterized by erratic fire spread, prolific spotting, and the formation of pyroclouds. The factors that contributed to this outbreak of extreme wildfires are sought in the combination of (1) antecedent meteorological conditions that allowed for the accumulation and extreme dry-out of fuels, and (2) concurrent adverse fire weather that enabled the wildfires to couple with the atmosphere and evolve into extreme pyroconvective events. Both topics serve as the motivation of this work, which presents a preliminary analysis of the extreme early August 2021 wildfires in Greece. The analysis was conducted employing ground-based and spaceborne observations. Results indicate the build-up of large potential for the occurrence of extreme wildfires in the affected regions since at least the beginning of the 2021 fire season. Our overarching goal is to consolidate the need for early detection and warning of elevated potential for extreme pyroconvective events, which are becoming a globally increasing concern due to inter alia climate change. The presented work was conducted in the frame of the CLIMPACT and FLAME (project number: 00559) research projects.

How to cite: Giannaros, T., Papavasileiou, G., Lagouvardos, K., Kotroni, V., Dafis, S., Karagiannidis, A., and Dragozi, E.: Lessons learned from the extreme wildfires of early August 2021 in Greece, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-5727, https://doi.org/10.5194/egusphere-egu22-5727, 2022.

The Eastern Alps are an important tourist destination and attract many visitors every year for their scenic beauty, sports attractions and rich cultural heritage. Tourism is an important source of income and contributes to the revival or maintenance of local traditions. However, tourism also has potential negative impacts on the regions, for example Austria's largest forest fire in Hirschwang near Reichenau an der Rax (district of Neunkirchen) in the period 25.10.2021 to 6.11.2021 was anthropogenically triggered by tourists.

In addition to the anthropogenic factors, the increase in extreme weather events caused by climate change and its scale dependent variations are a major challenge in the preparation of wildfire risk maps.

Wildfires in steep Alpine valleys behave differently than those on flat or moderate inclined slopes. The present work describes a wildfire that occurred in August 2018 in a famous world-heritage site in Austria (Melzner et al. 2019), which was presumably initiated by a carelessly discarded cigarette or the reflection of a broken glass bottle at the foot of the rockwall. Indicators of fire severity and rockfall occurrence during and after the fire are described.

The vertical rockwalls, the anabatic winds and patchy vegetation pattern, caused an upward jumping of the fire resulting in a spotty fire pattern. This most probably resulted in spatially varying fire intensities, and consequently highly heterogenic changes in soil and rockmass structure. The wildfire clearly showed that wildfires can have a significant impact on ecosystems and pose a high risk to settlements in the Alpine area. The rockfall hazard and risk assessment conducted in 2014 (Melzner 2015) enabled a fast decision making as part of an emergency response during and after the wildfire catastrophe in terms of identification of possibly endangered houses and planning of preliminary rockfall preventive measures.

How to cite: Melzner, S., Shtober-Zisu, N., Katz, O., and Wittenberg, L.: Characteristics of wildfires in the Eastern Alps, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-6435, https://doi.org/10.5194/egusphere-egu22-6435, 2022.

The identification of the type and extent of the area damaged by natural hazards such as wildfires using Earth Observation data can contribute to a better understanding of the processes affecting the Man-Nature system and, thereby, Man’s capability for sustainable land management. Fire effects are not limited to vegetation and litter cover and composition but include topsoil properties, both of which contribute to the enhanced hydrological and geomorphological activity typically observed in recently burnt areas. The present study focusses on fire-induced changes in topsoil properties, vegetation and ground cover and how this latter parameter can be acquired via satellite multi- and hyperspectral analysis for the determination of soil erosion model ground cover inputs. This objective has been achieved via the comparison of field ground cover data with multi and hyperspectral satellite derived data. Hence, we applied both types of ground cover data – i.e. field and satellite-based to the same erosion model to assess how the different model input values affected the differences between predicted and observed soil erosion rates.
To this end, the present study applied the modified Morgan-Morgan-Finney (MMF) erosion model to a pine plantation that had recently been burnt by the dramatic, June-2017 Pedrógão wildfire in Central Portugal. The MMF model was calibrated against the observed plot-scale erosion rates and the seasonal patterns therein, operating on the effective hydrological depth, fire severity impact and ground cover. Furthermore, we tested satellite and field based burn severity assessments and compared both model predictions with the field erosion measurements at plot scale. Additionally, the MMF input parameters linked to vegetation cover were estimated from field observations as well as various remotely-sensed indexes derived from Sentinel-2 MSI (MultiSensing Instrument) and PRISMA (HyperSpectral Precursor of the Applicative Mission) hyperspectral data. The results showed that remote sensing data can provide valuable estimates of post-fire vegetation recovery for parameterization of the MMF model for the first post-fire year. An important condition, however, is that the spatio-temporal resolution of the satellite-based data match the spatial patterns in fire severity on the one hand, and, on the other, the changes in soil erosion processes with time-since-fire. Therefore, factors such as pre-fire fuel load, vegetation composition and topsoil properties will require careful consideration when extrapolating the current results to other burnt areas.

How to cite: Lazzeri, G., Vieira, D. C. S., González-Pelayo, O., Frodella, W., Keizer, J. J., and Moretti, S.: Ground cover retrieval with Hyper- and Multi- spectral data fusion for post-fire soil erosion modelling - The Castanheira de Pêra study site., EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-6561, https://doi.org/10.5194/egusphere-egu22-6561, 2022.

Slash-pile burning is a common practice in land management across the Mediterranean environment mainly for removing unwanted biomass. This practice is known to have negative effects on topsoil due to high temperatures.  However, the impact on water quality has often been neglected. To address this issue, two experimental burns were conducted: one with moderate (MS), and one with high (HS) severity, to monitor the impact of these practices on water quality. The unburned (UB) treatment, was set aside from the burn treatments. The natural vegetation is composed of Maquis shrubland and meadow plants (Foeniculum vulgare Mill., Elymus repens (L.) Gould, Digitaria sanguinalis (L.) Scop.). The soil type is classified as Leptosol and has a silty clay loam texture with 11.5%, 58.9%, and 29.6% of sand, silt, and clay content, respectively. Treatments were carried out on a sloping terrain (~ 18 °) characteristic of the Mediterranean landscape. Runoff and erosion samples were collected 22 times during the two-year study after major rainfall events. The properties studied were: surface runoff, sediment yield, total carbon in sediment (TC), and water quality parameters such as pH, electrical conductivity (EC), and concentrations of bromine (Br¯), chloride (Cl¯), sulfate (SO₄²¯), phosphate (PO₄³¯), fluoride (F¯), potassium (K⁺), sodium (Na⁺), calcium (Ca²⁺), and magnesium (Mg²⁺). Overall, changes in water quality were consistent with the effects of burning in the first post-burn months, while runoff and sediment yield were more dependent on precipitation patterns, regardless of vegetation cover in the later sampling period. TC had higher levels in HS than in MS, and was increased in both burn treatments at later sampling dates. In the context of changes in water chemistry, the observed effect was more pronounced in HS, while the hydrological response showed high levels in MS. However, the UB also showed significant changes in water quality following major rain events, which was attributed to soil saturation. Our research suggests that slash-pile burning has negative impact on water quality, and it is recommended that biomass be used in other ways, especially in the context of soil and water conservation.

Keywords: burning, runoff, rainfall, vegetation, water conservation

Acknowledgment: The work was supported by the Croatian science foundation under the project “Influence of Summer Fire on Soil and Water Quality” (IP-2018-01-1645).

How to cite: Delač, D., Kisić, I., Zgorelec, Ž., Perčin, A., and Pereira, P.: Water quality response to slash-pile burning in a Mediterranean environment (Croatia), EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-1096, https://doi.org/10.5194/egusphere-egu22-1096, 2022.

With current global warming, the exacerbation of climate change and the progression of neglect in rural areas, forest fires are increasing in extent and severity. To alleviate these changes in the fire regime and seek the reduction of large severe fires, the use of fire as a preventive management tool is being implemented through the application of prescribed burns in Mediterranean forests, used in forestry actions to reduce the understory and break both vertical and horizontal continuity of fuels. In this study we want to see the efficacy of the treatment by determining the effects of the prescribed burns on the soil, both physical-chemical and biological parameters, as well as on the vegetation, in a semi-arid forest ecosystem. The prescribed burns were performed in the municipality of Ayna, Albacete (SE Spain). To evaluate and monitor the ecological damage to the soil in the short term (1 year), CO2 flow measurement cameras were used to measure soil respiration, mini-disk infiltrometers, with a monthly monitoring period throughout the year. The results do not show significant alterations in all the parameters studied due to these prescribed burns over a long period, stabilizing together with the unburned plots. However, in the short period of time (3 months later), some variables are affected. This study aims to observe, and make known, the effects that these actions have on the soil, being these of great relevance to carry out a design, management, and application of these tools to forest management in the Mediterranean area.

How to cite: Fajardo, Á., Moya, D., Peña, E., Plaza-Álvarez, P., González, J., Díaz, A., Botella, R., Borja-Lucas, M.-E., Gómez, E., and De las Heras, J.: Effects on soil and vegetation of prescribed burn in the southeast of the iberian peninsula, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-2469, https://doi.org/10.5194/egusphere-egu22-2469, 2022.

Wildfire in peatlands is of global importance due to the risk of direct carbon release. While considerable attention is given to carbon release, other wildfire impacts and indirect risks, such as the impact on soil pH, remain less studied. Peatlands characteristically require acidic conditions (soil pH ≤ 4.5) for optimal functioning. However, wildfire-produced ash often has a high pH and ash input into soil could potentially increase soil pH.

We studied a wildfire in a raised-bog peatland in the south of the Netherlands – where considerable peat smoldering and ash production occurred – by combining field observations with lab experiments. We measured the pH of topsoil and ash samples, which were collected from the area approximately two months after the wildfire. A smoldering experiment with peat was done to estimate the alkalinity in freshly produced ash (herein: ‘fresh ash’) and to able to compare it to ash collected in the field (herein: 'aged ash'). Finally, the amount of fresh ash needed to increase soil pH was quantified in an incubation and titration experiment with ash and peat soil.

All topsoil samples collected from the field were acidic (pH ~3-4), even in sampling locations with ash present. Fresh ash produced in the smouldering experiment was alkaline, while aged ash collected during field work was slightly acidic. This indicates that alkalinity was likely leached from the ash by the time of field work. The incubation experiments showed that a ≥3 cm ash layer is needed to increase soil pH by at least 1 unit. Results suggest that ash, when produced in high enough quantity, can change peatland soil pH. However, dilution and ageing of the ash after a wildfire, as likely occurred in our field site, will constrain the period of elevated soil pH after wildfires and subsequent ash input. This transit increase in soil pH suggests that even wildfires with considerable ash production do not lead to increased soil pH.

How to cite: Marcotte, A. L., Limpens, J., Stoof, C., and Stoorvogel, J.: The impact of peatland wildfires on soil acidity, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-11713, https://doi.org/10.5194/egusphere-egu22-11713, 2022.

Ash and sediments transported by post-fire runoff are a source of hazardous substances, like metals, posing a risk of contamination to the downstream aquatic ecosystems. In the present study, metal mobilization was evaluated using 16 m² bounded runoff-erosion plots at a eucalypt plantation in Albergaria-a-Velha (Aveiro district, North-Central Portugal) that burnt with moderate severity in September 2019. In total, 9 plots were installed: 3 were treated with eucalypt chopped-bark mulch, another 3 were treated with an innovative barrier-based technique developed within the scope of the LIFE REFOREST project (LIFE17 ENV/ES/000248) consisting of geotubes containing a mycotechnosol and, 3 others were left untreated. Eroded sediments and overland flow were collected during the first post-fire hydrological year. Sediment and overland flow samples were analysed for vanadium (V), chromium (Cr), manganese (Mn), iron (Fe), cobalt (Co), nickel (Ni), copper (Cu), zinc (Zn), arsenic (As), cadmium (Cd) and lead (Pb), which are of concern for both environmental and human health. Given the most recent climate change scenarios, which foresee an increase in fire severity and frequency for the Mediterranean region, this work provides key information for resource managers to define adaptative strategies to effectively safeguard surface water resources.

How to cite: Serpa, D., Machado, A., Campos, I., Santos, M., Jesus, F., Oliveira, B., Gholamahmadi, B., Martins, M., González-Pelayo, O., Abrantes, N., Keizer, J., and Consortium, L.-R.: Post-fire metal exports in a recently burnt eucalypt plantation in North-Central Portugal, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-12625, https://doi.org/10.5194/egusphere-egu22-12625, 2022.

Wildfires are documented to affect physical, chemical and biological properties of topsoil. Besides through the direct heating-induced impacts, wildfires can also affect topsoil properties indirectly through the ash layer deposited on the soil surface immediately after fire. These indirect ash effects are less well understood, because of the marked dynamics in ash loads with time-since-fire due to mobilization by wind and water erosion. Therefore, we took advantage of a lysimeter study - a controlled experiment under field conditions - into the mobilization of ashes by overland flow, to address the ash impacts on topsoil nutrient contents. The lysimeter study involved a total of 15 lysimeters with a surface area of 50 cm by 120 cm and at a slope angle of approximately 10°. The lysimeters were equally and randomly distributed over five treatments. Four treatments involved the application of two types of ash at a rate of 500 g.m^-2 on a 2-3cm-thick layer of soil (in fact, sediments from the Mondego river), while the fifth, control treatment did not. One ash type consisted of black ashes collected in a 2020 burnt mature pine plantation in north-central Portugal, while the white ashes were obtained from a paper mill factory. In turn, two treatments per ash type involved the presence vs. absence of a 10cm-wide strip of 1cm-diameter PVC bars with a density of 1000 bars per m^-2, mimicking a riparian vegetation zone and, assess its effectiveness to retain eroded ashes preventing them from entering streams. The lysimeter experiment ran for 7 weeks, starting on September 6 (ash application) and ending on 22 October 2021, covering the period that typically corresponds to the initial phase of the post-fire window-of-disturbance in the study region. At the end of the experiment, the upper 2cm of the soil were sampled at 3 locations within each lysimeter, in its middle and halfway its upper and lower halves. This was done after removing the remaining ashes on the soil surface. All soil samples were analysed for their contents of available Phosphorus (Pav) and total Nitrogen (TN) but, at this moment, only the Pav analyses have been concluded. The preliminary Pav results revealed a much smaller enrichment by the black than white ashes. The median Pav contents were 4.6 microgram per gram of soil for the control lysimeters as opposed to  5.6 and 9.2  microgram per gram of soil for the lysimeters with black and white ashes, respectively.  This difference in enrichment could be linked to the differences in Pav content of the two ash types, being 1.9 and 1.0 microgram per gram of the white and black ash, respectively. Furthermore, the Pav enrichment was not affected by the presence/absence of the simulated riparian zone at the bottom of the lysimeters, as the differences in Pav contents of the lysimeters with and without these zones amounted to 0.1 microgram Pav per gram of soil in the case of both the black and the white ashes.

How to cite: Simões, L. B., Silva, J., Macedo Godoy, L., Machado, A. I., Martins, R., Campos, I., and Keizer, J. J.: A lysimeter study of nutrient mobilization from wildfire and factory ashes by overland flow and soil leaching, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-9680, https://doi.org/10.5194/egusphere-egu22-9680, 2022.

Wildfires are now widely documented to produce strong to extreme runoff and erosion responses during the so-called window-of-disturbance. However, the role of wildfire ash in post-fire runoff generation and especially the contribution of wildfire ash to post-fire erosion rates are still poorly studied. The same applies for the effectiveness of erosion control measures to reduce ash mobilization by runoff. To address these knowledge gaps, we carried out a lysimeter experiment in which overland flow and the associated transport of sediments and ashes was compared for five treatments. Four treatments involved the application of black ash from a wildfire or white ash from a paper pulp factory, both with and without a simulated riparian strip at the bottom of the slope, while the fifth treatment was the control without ash as well as without the riparian strip. Each of the five treatments was applied to three randomly selected lysimeters. The lysimeters had a surface area of 50 cm by 120 cm, a slope angle of approximately 10 degrees and were topped up with a 2-3cm-thick layer of soil (in fact, sediments from the Mondego river) over a sand and a gravel layer. Overland flow was collected at the bottom of the lysimeters and diverted into a tank using a garden hose. The experiment started on 6 September 2021 with the application of the ash at a rate of 500 g m-2 and ended on 22 October 2021, coinciding with the initial phase of the post-fire window-of-disturbance in the study region. During this 7-week period, overland flow was measured at a total of five occasions following significant rainfall events and, whenever possible, samples collected for laboratory analysis of their concentration of total suspended sediment (TSS) and their organic matter fractions.  The preliminary results for the lysimeters without riparian strip suggested that the two types of ashes played contrasting roles in overland flow generation. The average amount of overland flow over the 7-week period was higher for the lysimeters with white ashes than for the control lysimeters (36.0 vs. 31.2 l), while the opposite was true for the lysimeters with black ashes (26.8 l). These differences in overland flow were associated with differences in TSS concentrations that were the opposite, averaging 11.7 and 20.4 g l-1 over the entire study period in the case of the lysimeters with white and black ashes, respectively. The overall TSS concentrations also suggested a marked role for the riparian strips but only in the case of the black ashes, dropping to 15.3 g l-1. In the case of the white ashes, the overall TSS concentrations were the same with as without the riparian strips.

How to cite: Macedo Godoy, L., Beatriz Simões, L., Machado, A. I., Martins, R., Campos, I., and Jacob Keizer, J.: Mobilization of black and white ashes by overland flow and their retention by riparian vegetation - preliminary results from a lysimeter experiment, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-9699, https://doi.org/10.5194/egusphere-egu22-9699, 2022.

Globally, high erosion rates are being triggered by extreme rainfall/runoff events. Ashes and char, by-product of devastating wildfires are the first particles mobilized and depleted. The contribution of the ash/char layer to the overall erosion process is still unestablished especially since separating ash and char fraction from litter, soil and eroded sediments is far from trivial. To address this knowledge gap, ASHMOB project (CENTRO-01-0145-FEDER-029351) is studying the mobilization of wildfire ash by wind and water erosion under controlled laboratory conditions as well as field conditions. The present study aims at contributing to the current knowledge on the physical process behind the mobilization of ashes and char when subject to runoff. This research is the second phase of the physical experiments on the mobilization by water of wildfire ash and char, performed at the Laboratory of Hydraulics, Water Resources and Environment of the University of Coimbra. To characterize ash erosion, a multi-channel flume was used (i.e., 5 parallel equal channels), which runs 5 replicate run-on events with exactly the same hydraulic conditions. To collect the full sample, a cart with trays moved at an established and controlled pace under the flumes, allowing the collection of water, ashes and sediments, thus characterising both hydrographs and ash yields for all event and replicate. Temporal resolution was fixed at 20 seconds per tray. Six major variables were tested: (1) Ash depth; (2) Type of burnt vegetation; (3) Ash layer length; (4) Ash particle size; (5) Slope. Preliminary results show that: (1) Smaller ash depths require lower flows to be mobilised by; (2) Pinus pinaster and Eucalyptus globulus have a different behaviour from Arbutus unedo ashes as the former tend to be transported more as a "aggregated block or chunk", possibly due to buoyancy, and the latter more like sediments; It was also observed that a higher number of large particles of char tend to provide a somewhat larger protection to the finer ashes than having little or no large particles of char; (3) a longer, in the flow direction,  layer of Arbutus unedo ashes has little to no impact in the mobilisation process, whereas for the other vegetations, a longer layer implies less transport relative to the initial amount of ashes; (4) smaller particle sizes, when left without the "protection" of larger char particles are transported more easily; (5) Slope has a large impact on the transport of ashes, especially when considering the same bed roughness.

How to cite: Martins, R., Keizer, J., Gama, I., de Lima, I. P., and de Lima, J. L. M. P.: Wildfire ash mobilization by run-on under controlled laboratory conditions: Qualitative analysis, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-9851, https://doi.org/10.5194/egusphere-egu22-9851, 2022.

Wildfires have historically been a natural alteration in Mediterranean ecosystems. Despite these ecosystems' high resilience, the expected climate change scenarios may lead into more recurrent and severe wildfires, and erosion and degradation processes can be enhanced.

Post-fire restoration measures, seek to minimize wildfire negative impacts on the burned area as well as its ecological rehabilitation. Among these measures, soil stabilization treatments like erosion barriers or mulching are key for erosion and flood control. Nevertheless, its economic viability can be limited, and therefore these treatments must be thoroughly evaluated considering their costs and their efficiency to achieve the objective. Additionally, there is a need to evaluate new techniques, which can be implemented in places where, due to the scarce vegetation, some traditional treatments as log barriers cannot be implemented.  This study seeks to evaluate the cost-efficiency of alternative post-fire emergency measures for erosion control in a semi-arid Mediterranean area.

The study area is located in the SE of Spain, more specifically in Hellín (Albacete). Wildfire took place on July 27 of 2020, and severely affected 266 ha of Pinus halepensis forest. Soil erosion was measured in 9 different micro-catchments (≈0.5 ha) located in the burned area. Three groups of micro-catchments were created, and a different treatment was randomly applied to each group. The applied treatments were the combination of straw mulch (0.25 kg/m²) with contour-felled logs (ML), and prefabricated biodegradable barriers (350 m/ha), Easy-Barriers ® (EB). The last three micro-catchments were designated as control and no treatment was applied.  At the outlet of each micro-catchment, sediment traps were settled to measure sediment yield. Additionally, rainfall intensity and erodibility were measured with pluviometers installed on the field.

The outcomes of the experiment, show that only the ML treatment resulted in a significant reduction (Kruskal-Wallis H test) of the eroded sediment for the first 15 months after fire. For the studied period, a total mean eroded sediment of 9.61 and 8.41 ton/ha was measured at the control and the EB traps respectively, while at the ML traps this amount was significantly lower (1.43 ton/ha).  The difference between the two applied treatments increased as the rainfall events occurred, due to the breaking of the EB and the transport downstream of the sediment they were retaining. Therefore, the measured sediment yield at the EB traps during the autumn of the second year was higher than in the control ones. According to these results, ML must be considered as an effective treatment to soil stabilization, whereas EB did not perform as expected. That underlines the need to improve the strength and durability of the EB, as their aim is to hold on until the vegetation recovery is sufficient to retain those sediments. As well, the efficiency of the combination of EB with mulch treatments should be studied as the use of EB considerably reduce costs and allows managers not to depend on the availability of material to place contour-felled logs throughout the burned area.

How to cite: González-Romero, J., Lucas-Borja, M. E., Plaza-Álvarez, P., Gómez-Sánchez, E., Fajardo, A., Moya, D., Peña-Molina, E., Ferrandis, P., Botella, R., Díaz-Montero, A., and De las Heras, J.: Alternative post-fire emergency measures efficiency for soil erosion control in semi-arid Mediterranean environments., EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-11586, https://doi.org/10.5194/egusphere-egu22-11586, 2022.

Extreme erosive responses after wildfires and the effectiveness of so-called emergency stabilization measures have been poorly quantified for convergent hillslopes and catchments, especially in comparison with (micro)plots and planar hillslopes. Yet, in Portugal, the barrier-based measures have been preferred in operational emergency stabilization. This recent study assessed the effectiveness of log barriers at reducing post-fire erosion at the swale scale within the framework of the INTERREG-SUDOE project EPyRIS (SOE2/P5/E0811). The study was conducted in Penouços (Aveiro, central Portugal), in an area burned by a wildfire in early September 2020, affecting 2035 ha. Before the first rainfall event after the wildfire occurred, three pairs of swales (0.3-2.7 ha), located in the part of the burned area managed by the Portuguese Nature Conservation and Forests Institute, were instrumented at their outlets with sediment fences. The magnitude of the erosion produced at each micro-catchment after the first post-fire rainfall was the criteria on which it was decided how many barriers needed to be installed and in which swale. In this way, 2, 1 and 4 barriers were installed in swales 2, 4, and 5, respectively, because of their higher sediment delivery, while swales 1, 3, and 6 were left untreated and used as control.

Over the first post-fire year, only swale 4 wasn’t producing less sediment than the respective control, swale 3, in absolute terms. Yet, in relative terms, the three swales with the barriers are producing 0-1 % of the sediment yields prior to the barriers’ installation. The initial, pre-treatment ratio of the erosion rates of the to-be-treated swale divided by the erosion rates of the paired untreated swale ranged from 6.3 for pair 2/1 to 10.4 for pair 4/3. Over the post-treatment period, the ratios markedly decreased, to 7.5 in the case of pair 4/3 and even well below 1 in the case of pairs 2/1 (0.1) and 5/6 (0.5). To validate these estimates of mitigation effectiveness, the sediments deposited at the upstream side of the barriers were collected at the end of the first post-fire year. The deposited sediments varied widely between the six barriers, from 8.9 to 192 kg, as well as between the three treated swales, from 8.9 to 462 kg. When summing the deposited sediments to the results of the outlets, the total sediment production is 606, 99.6, and 4271 kg/ha on swales 2, 4 and 5, respectively. These indicate that the sediments collected in the outlet of the swales represent only 24, 66 and 34% of the total sediments redistributed within the micro-catchment.

This poster will present the detailed differences of the sediment production in each paired micro-catchment during the first post-fire year and the efficiency of the barriers as an emergency stabilization measure discussing them in function of terrain characteristics and rainfall regime.

How to cite: Silva, J., Girona-Garcia, A., Augustijn, M., Machado, A., Martins, R., Martins, M., Basso, M., Simões, L., Cretella, C., Vieira, D., and Keizer, J.: Effectiveness of log timber barriers to reduce erosion from terraced swales, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-9293, https://doi.org/10.5194/egusphere-egu22-9293, 2022.