SSS9.6

The Canadian Fire Weather Index (FWI) is a meteorologically based index designed initially to be used in Canada but it can also be used worldwide, including the Mediterranean, to estimate fire danger in a generalized fuel type based solely on weather observations. The four weather variables are measured and used as inputs to the FWI (rain accumulated over 24 h, temperature, relative humidity, and wind speed) are generally taken daily at noon local standard time.

Recent studies have shown that temperature and precipitation in the Mediterranean, and more specifically in Greece are expected to change, indicating longer and more intense summer droughts that even extend out of season. In connection to this, the frequency of forest fire occurrence and intensity is on the rise. In the present study, the FWI index is used in order to assess changes in future fire danger conditions.

To represent meteorological conditions, regional EURO-CORDEX climate model simulations over the Mediterranean and mainly Greece at a spatial resolution of 11 km, were utilized. In order to assess the impact of future climate change, we used two Representative Concentration Pathway (RCP) scenarios consisting of an optimistic emission scenario where emissions peak and decline beyond 2020 (RCP2.6) and a pessimistic scenario where emissions continue to rise throughout the century (RCP8.5).  We compare the FWI projections for two future time periods, 2021-2050 and 2071-2100 with reference to the historical time period 1971-2000. Based on the critical fire risk threshold values that have been established in previous studies for the area of Greece, the days with critical fire risk were calculated for different Greek domains.

How to cite: Rovithakis, A., Voulgarakis, A., Grillakis, M., Giannakopoulos, C., and Karali, A.: Future Climate Change Impact on Wildfire Danger over the Mediterranean: the case of Greece, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-11198, https://doi.org/10.5194/egusphere-egu21-11198, 2021.

The objective of this study was to compare the impact of Scots pine (Pinus sylvestris L.), European larch (Larix decidua Mill.) and common birch (Betula pendula Roth) on the properties of regenerated soils in a reforested post-fire site in southern Poland (Central European conditions). The samples of O horizons (litter) and uppermost mineral soil (0-5 cm) were taken under pure stands of investigated tree species, aged from 26 to 27 years old and growing on sandy and loamy soils. In the litter samples, the pH, carbon and macronutrient (N, Ca, Mg and K) content were determined. The mineral soil samples were measured for texture, pH, soil organic carbon (SOC), total nitrogen (N_t), exchangeable acidity (Hh), basic exchangeable cations (Ca²⁺, K⁺, Mg²⁺, Na⁺) and cation exchangeable capacity (CEC). The obtained results indicated that the effect of tree species on soil properties was evident. The litter layers under birch had a higher pH and a lower C:N ratio, and they contained more N, P, Ca, and Mg than the litter layers under pine and larch. In the mineral soil, birch brought about a higher accumulation of SOC and CEC than the studied coniferous species. Higher SOC accumulation in mineral soil under birch was related to higher acidity under the species compared with the conifers. Soil texture in the studied range - from sands to loams - had only a limited effect on the properties of the studied post-fire soils. Thus, our results indicate that the tree species used for the reforestation of post-fire sites are crucial to the properties of regenerating soils and restoring the ecological functions of soils. Among the studied tree species, the common birch has the most pronounced effect on soil properties, and this is especially significant because the species has appeared by spontaneous succession.

The study was financed by The National Science Centre, Poland, Grant No. 2018/31/D/ST10/02137.

How to cite: Woś, B., Józefowska, A., Likus-Cieślik, J., Chodak, M., and Pietrzykowski, M.: Impact of different tree species and soil texture on physicochemical properties, carbon and macronutrient content of post-fire forest soils, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-7561, https://doi.org/10.5194/egusphere-egu21-7561, 2021.

Boreal forests are among the ecosystems most significantly impacted by wildfires as a consequence of climate warming. A large proportion of the global boreal forest area is located in Siberia, however, its vast extent and restricted access limit datasets recording changes in wildfire activity, especially from a longer-term perspective. Such long-term records of wildfire activity are vital to understanding how fire regimes vary with changes in climate, vegetation composition and human-vegetation interaction, as well as the impacts of wildfires on boreal forests.

Here, we explore how patterns in fire regime (biomass burned, fire frequency, fire type) have changed over the Holocene. We focus on the relationship between fire regime, forest density and the fire-related traits of the main tree species, and peatland hydrology. We used charcoal-morphologies based reconstructions of fire regimes, along with pollen-based assessments of vegetation composition and testate amoebae-based hydro-climate reconstructions in Pinus-Betula dominated peatlands from central-western Siberia, Tomsk Oblast, Russia.

The occurrence of more severe fires (i.e., higher biomass burning per fire episode and abundant woody morphotypes) were recorded between 7500 and 5000 cal yr BP. Higher temperatures during that time, likely enhanced peatland dryness and fuel flammability creating conditions conducive to peat and forest fires. Drier peatland conditions also affected forest composition and density by favouring the expansion of a mix of light taiga and fire resisters (e.g., Pinus sylvestris, P. sibirica, Larix) with denser taiga and fire avoiders (Picea obovata and Abies sibirica) on the peatland. A shift to the lowest biomass burning and fire types affecting mostly litter and understorey vegetation, was registered between 4000 and 1500 cal yr BP. Temporally, it coincides with an increase in peatland surface moisture and a change in forest composition characterised by a decline in fire resisters, while fire avoiders remained abundant. An almost synchronous intensification in fires frequency and severity from ca. 2000 cal yr BP to the present at all sites, was concurrent with the rise to dominance of fire-invader species (Betula), as well as a more abundant biomass in the understory layer (shrubs, herbs, ferns, moss), while fire resisters and avoiders declined substantially. We found that Picea obovata to be highly vulnerable tree taxa to frequent, severe fires.

This long-term perspective demonstratesthat peatland hydrology is connected to, and feedbacks on peatland and forest composition and fuel dryness and ultimately fire regime. It also shows that more frequent fires of higher severity can lead to compositional or structural changes of forests, if trees cannot reach reproductive ages prior to the next burning events. Future predicted increases in temperatures are likely to enhance peatland drying, with cascading effects on forest and peat plant composition, subsequently exacerbating wildfire activity. This study thus contributes to an understanding of disturbance regimes in boreal forests and considers their potential to adapt to new climate conditions and fire regimes.

How to cite: Feurdean, A., Diaconu, A.-C., Butiseaca, G., Galka, M., Hutchinson, S. M., Kirpotin, S., Pfeiffer, M., and Tonkov, S.: Interaction between peatland moisture and plant functional types drives fire dynamics in forested peatlands in central-western Siberia, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-12975, https://doi.org/10.5194/egusphere-egu21-12975, 2021.

Wildfires have an important influence on desertification’s advance. Due to climate change, it is foreseeable that the number of wildfires and their burned surface will increase. The alteration of fire regimes and its effect on the vegetation recovery, soil properties and fuel structure are one of the imperative research needs at this time to be able to establish vegetation vulnerability limits or ranges and vegetation resilience against forest fires.

The aim of this study is to implement a conceptual model assessment of vegetation vulnerability and-or vegetation resilience after forest fires. It starts with a bibliographic research to establish the concepts and definitions of vulnerability and resilience, with which undertake the practical case of generating a model or an indicator of resilience and vulnerability from the effects that the severity and recurrence of forest fires have had in two large forest fires in the southeast of Spain in 1994 and 2017. From the processing of the satellite scenes within the Google Earth Engine platform, several spectral vegetation indices are calculated such as NDVI, NBR or dNBR and four zones belonging to the Habitat type 9540 of Annex I of Directive 92/43/EEC are digitalized depending on their fire severity and fire recurrence: not burned in 1994 and burned in 2017; burned in 1994 and not burned in 2017; burned in both 1994 and 2017 and, finally, not burned in both 1994 and 2017. From this design a time series graph is made to evaluate the vegetation recovery rate in each of the areas.

Once this is done, it is possible to check how many years each zone requires to recover the spectral values before wildfires, which zones require more time to get recovered and, depending on the severity values, which zones should be treated to improve its natural recovery. With all the results, the last process is to create the cartography for identifying the most vulnerable zones depending on their ecological characteristics so we can be aware and do preventive treatments to increase the resilience of those most vulnerable areas in future extreme events. Google Earth Engine has proved to be an extremely useful tool for managing big datasets due to its high-level processing, versability and reproducibility, because once the script is done it is way easy to update the current study or to implement the same case of study in other areas to compare both results.

How to cite: Peña Molina, E., Marino del Amo, E., Tomé Morán, J. L., Moya Navarro, D., and de las Heras Ibañez, J.: Conceptual model assessment of vegetation vulnerability to fire in SE Spain: severity and recurrence effects using Google Earth Engine, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-14466, https://doi.org/10.5194/egusphere-egu21-14466, 2021.

Forest fires are a global problem that affects almost all parts of the world. Southern Europe has been a fire prone area since prehistoric times. The northwest of the Iberian Peninsula, despite being an area abundant in rainfall, is currently a hotspot for forest fires. Forest fires produce carbon and ash as a result of the combustion of vegetation, these products can affect the germination behavior of plants.

Due to climate change, forest fires are becoming more severe, more intense and more recurrent, and this context of disturbances facilitates and accelerates the replacement of native species by invasive alien species in many forest ecosystems. For this reason, we propose to compare the role of carbon and ash in the germination of two native species versus two invasive alien species. The two selected native species were Pinus pinaster Aiton and Salix atrocinerea Brot. and the two invasive species Paraserianthes lophanta (Willd.) I.C. Nielsen and Acacia melanoxylon R. Br. For it, 5 concentrations of ash and 1 concentration of carbon from 2 different origins (carbon from the same studied species and carbon from Ulex europaeus L.) were applied to seeds of these species. Mainly it stands out that the control germination of the native species was higher than that of the invasive species and the germination obtained under ash or carbon treatments was always similar or lower than the control germination. The germination obtained with the carbon of the own species was similar to the control germination and significantly higher than that achieved with the carbon of U. europaeus. Germination timing depends on each species studied, and invasive species take longer to complete their germination than native species (30-42 days versus 80-125 days). The carbon of the own species did not modify the germination timing while the carbon of Ulex did it in the two native species.

Therefore, carbon and ash are two factors that modify the germination behavior of both the native species and the invasive species studied and can be used to manage plant regeneration after forest fire.

Funding. This work was supported by the Spanish Ministry of Science, Innovation and Universities, the Castilla y León Regional Government, the Galicia Regional Government and the European Regional Development Fund (ERDF) in the framework of the FIRESEVES (AGL2017-86075-C2-2-R) and WUIFIRECYL (LE005P20) projects and the Competitive Reference BIOAPLIC (ED431C2019/07) and the Strategic Researcher Cluster BioReDeS (ED431E 2018/09).

How to cite: Cruz, O., Reyes, O., and F. Riveiro, S.: Effect of charcoal and ash from forest fires on the reproductive behavior of two native species versus two invasive species., EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-7273, https://doi.org/10.5194/egusphere-egu21-7273, 2021.

Fire is an ecological factor that affects ecosystem structure and functioning and determines later recovery of the ecosystem through the modification of biological processes, such as seed germination and seedling establishment. Another factor that modifies ecosystems is the presence of invasive alien species, which easily colonize new habitats after disturbances such as forest fires. Within this research, we analyzed the germination response to fire trough carbon and ash of three species that share habitat, one native species (Daucus carota L.) and two invasive alien species (Helichrysum foetidum (L.) Moench and Oenothera glazioviana Micheli) to identify and compare the effects of carbon and ash on the germination of these three species. For this purpose, germination tests were performed by using seeds treated with carbon and five concentrations of ash (from lower to higher -Ash1, Ash2, Ash3, Ash4, Ash5-), simulating remanent conditions after forest fires. Carbon and ash were obtained from the native species Ulex europaeus due to its abundancy in Atlantic shrubby ecosystems.

In control conditions, germination of the three species studied was: D. carota (34.4%), H. foetdum (77.6%) and O. glazioviana (12.0%). The three species showed slightly different responses to fire factors. Carbon slightly reduced germination of native D. carota and stimulated germination of O. glazioviana, but statistically differences were not found with control. Germination response to ash depended on the species and the ash concentration applied. Lower concentrations of ash did not affect germination, intermediate concentrations reduced it, and higher concentrations inhibited germination at all. Regarding the species, both D. carota and O. glazioviana maintained its germination similar to control with Ash1 and Ash2, reduced it with Ash3, and inhibited it with Ash4 and Ash5. Germination of H. foetidum was the most affected. It only remained unaltered with Ash1 and was reduced progressively with Ash2 and Ash3. Treatments Ash4 and Ash5 totally inhibited it, as the other two species studied.

At high concentrations, ash prevented the germination of the three species. In contrast, carbon did not modify it. After a forest fire, with soil covered by carbon and ash, germination of this species would be reduced or even removed if the concentration of ash is high. The difference success in this species after a forest fire could be explained by the amount of seeds produced or its response to other fire factors as heat or smoke.

Funding. This work was supported by the Spanish Ministry of Science, Innovation and Universities, the Castilla y León Regional Government, the Galicia Regional Government and the European Regional Development Fund (ERDF) in the framework of the FIRESEVES (AGL2017-86075-C2-2-R) and WUIFIRECYL (LE005P20) projects and the Competitive Reference BIOAPLIC (ED431C2019/07) and the Strategic Researcher Cluster BioReDeS (ED431E 2018/09).

How to cite: F. Riveiro, S., Cruz, Ó., and Reyes, O.: Exploring the effects of carbon and ash derived from forest fires in relation to germination of two invasive alien species and one native species., EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-8239, https://doi.org/10.5194/egusphere-egu21-8239, 2021.

Recently burnt areas across the world have been documented to produce strong to extreme runoff and erosion responses. At the same time, they are well known to lose their typically blackish colour due to wildfire ashes (sensu latu, including char) relatively quickly during the early phases of the window-of-disturbance. The contribution of wildfire ash to post-fire erosion rates, however, remains poorly quantified. Arguably, this is first and foremost due to the difficulties of separating the ash and char fractions from the mineral soil fractions, at least at the routinely basis that is required for field erosion studies with high temporal resolution (say, less than 1 month) and an absolute minimum of three replicate plots per slope or treatment. To this end, the national ASHMOB project (CENTRO-01-0145-FEDER-029351) is trying to advance the knowledge of the mobilization of wildfire ash by wind and water erosion by studying it first under controlled laboratory conditions. The present study concerns the first phase of wildfire ash erosion by water, using Morgan cups to quantify the splash erosion of wildfire ash by high-intensity simulated rainfall in the Laboratory of Hydraulics, Water Resources and Environment of the University of Coimbra. More specifically, this study assessed the importance of the following factors in ash splash erosion: (1) extreme rainfall intensities, ranging from 150 to 450 mm/h; (2) source of the ash, from recently burnt woodlands dominated by maritime Pinus pinaster, Eucalyptus globulus, and Arbutus unedo; (3) ash depth or load. Preliminary analysis of the obtained results suggested that splash erosion of wildfire ash: (1) varied strongly with the applied rainfall intensity, increasing in a linear manner with increasing intensity; (2) differed markedly with the dominant tree cover, being clearly lower for the pine and eucalypt stands than for the strawberry tree stands, possibly due to the differences in soil burn severity as indicated by blackish and whitish ashes, respectively; (3) depended noticeably on ash depth, decreasing clearly with increasing ash depth and, arguably, with a greater damping capacity.

How to cite: Martins, R., Keizer, J., Abrantes, J. R. C. B., González-Pelayo, O., de Lima, I. P., and de Lima, J. L. M. P.: Wildfire ash mobilization by splash under simulated rainfall in controlled laboratory conditions, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-12765, https://doi.org/10.5194/egusphere-egu21-12765, 2021.

Wildfire ash is a mixture of pyrogenic organic and inorganic materials with high concentration in nutrients and potential contaminants that is easily mobilized by runoff. Ash has been identified as a major threat to water quality since it can impact aquatic life and disrupt water treatment operations when is washed off into water bodies. The ability to modelling ash transport, however, is in its infancy.  One reason for this is that the relationship between runoff and ash transport for concentrated flow has not been described yet, limiting the capabilities of current runoff-erosion models to predict ash transport and delivery in fire-affected areas.

To fill this knowledge gap, we conducted a series of laboratory experiments on ash transport using concentrated flow on flumes. Ash collected from US conifer forest burned at high severity was applied at two different rates (corresponding to layers of 1 and 3 cm thickness) to an artificial substrate of gravel and sand attached to the bottom of the flumes that simulates soil roughness. Three different flow rates were consecutively applied to each flume in all possible combinations (6 flow rate combinations and 6 replicates per combination and ash thickness).

The results show that ash is easily transported by concentrated flow, confirming previous observations on ash mobility. The runoff rate required to start transporting the ash was close to 0 (0.005 L min^-1 for both 1 and 3 cm ash layers) and the average concentration of ash in the runoff once this process started was considerably high (120 and 176 g L^-1 for 1 and 3 cm ash layers respectively), probably due to the low density and cohesion of this fire by-product. The results also show that ash depletion is a critical process when modelling ash transport and, thus, that ash transport by concentrated flow is better modelled using a variable sediment transport rate to account for ash decay with consecutive rainfall events. This is especially true for the 1 cm ash layer. The relationships between runoff and ash transport for concentrated flow obtained here for the evaluated ash type and loads are critical parameters to predict ash transport and will be used to refine ash transport capabilities of WEPPcloud-WATAR, a new tool aimed at predicting ash contamination risks after wildfires.

How to cite: Neris, J., Brown, R. E., Robichaud, P. R., Elliot, W. J., Santin, C., and Doerr, S. H.: Modelling wildfire ash transport by concentrated flow, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-15336, https://doi.org/10.5194/egusphere-egu21-15336, 2021.

Forested watersheds are critical sources of the majority of the world’s drinking water. Almost one-third of the world’s largest cities and two-thirds of cities in the United States (US) rely on forested watersheds for their water supply. These forested regions are vulnerable to the increasing incidence of large and severe wildfires due to increases in regional temperatures and greater accumulation of fuels. When wildfires occur, increases in suspended sediment and organic carbon can negatively affect aquatic ecosystem health and create many costly challenges to the drinking water treatment process. These effects are often largest in the first year following a wildfire. While past research has shown the likelihood of source water impacts from wildfire, the magnitude of effects remains uncertain in most regions. In our study, we will quantify the projected short-term effects of three large (>70,000 ha) wildfires on key water quality parameters (sediment and organic carbon) in two important forested source watersheds in the Cascade Range of Oregon, US. We calibrated and validated a modified Soil and Water Assessment Tool (SWAT) to simulate streamflow, sediment loads and transport, as well as in-stream organic carbon processes for a historical period prior to wildfire. The calibrated model parameters were then modified based on literature values and burn severity maps to represent post-fire conditions of the three large wildfires. The parameter adjustments for simulating wildfire will be validated with post-fire water quality field samples from the wildfires. We will present estimations of future water quality impacts in the burned watersheds under different precipitation conditions at a daily scale for the first year following the wildfires, which will provide testable hypotheses. Additionally, we will determine catchment characteristics most critical in determining the post-fire water quality response. This work will help predict the magnitude of effects from these historic wildfires, which can inform forest and drinking water management decision making.

How to cite: Wampler, K., Bladon, K. D., and Faramarzi, M.: Predicting Source Water Quality Following Wildfires Using Hydrologic Modeling, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-78, https://doi.org/10.5194/egusphere-egu21-78, 2021.

Wildfires constitute a diffuse source of contamination to aquatic ecosystems. In burnt hillslopes, ash and sediments transported by overland flow are a source of potentially hazardous substances, like metals, posing a risk for downstream water bodies. In the present study, post-fire metal mobilization by overland flow was evaluated in 16 m² bounded plots at a eucalypt stand in Albergaria-a-Velha (Aveiro district, North-Central Portugal) that burnt with moderate severity in September 2019. Overland flow samples were collected on a weekly to bi-weekly basis, depending on the occurrence of rain, during the first 6 months after fire. Aside from overland flow samples collected at slope scale, water and sediment samples were also collected in a fire-affected stream within the Albergaria burned catchment, to assess the contamination risk posed by the fire. Samples were collected at three sites along the stream: one upstream, one within and another downstream from the burnt area, after major rainfall events. The metals analysed in this study included, vanadium (V), chromium (Cr), manganese (Mn), iron (Fe), cobalt (Co), nickel (Ni), copper (Cu), zinc (Zn), arsenic (As), cadmium (Cd) and lead (Pb). Results showed that most metals exhibited a peak in exports immediately after the first significant post-fire rainfall event likely due to the wash-off of the ash layer and high sediment losses, but for some elements like Zn and Cu, exports were more or less constant over time. The fire seems to have had a low impact on the water quality of the affected stream, since metal concentrations were similar between the three study sites. The quality of stream sediments, on the other hand, was clearly affected by the fire, especially after the rainy season. As fire severity and frequency is forecasted to increase in the near future due to climate changes, the results of this work reinforce the importance of water managers to define adaptative strategies to effectively protect freshwater bodies.

How to cite: Serpa, D., Machado, A., Santos, M., Campos, I., Jesus, F., Oliveira, B., Gholamahmadi, B., Martins, M., González-Pelayo, O., Jacob Keizer, J., Abrantes, N., and Consortium, L.-R.: Post-fire mobilization of metals in a recently burnt area in North-Central Portugal: a contamination risk for waterbodies?, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-4929, https://doi.org/10.5194/egusphere-egu21-4929, 2021.

Wildfire events have severe effects over mountain environments, changing dramatically the local terrain hydrogeological conditions and frequently affecting slope stability. Besides burning vegetation, wildfires induce a modification on soil properties that could result in a decreased capacity of infiltration. This leads to an increase of erosion and, potentially, of the related geohazards, such as flash flooding and debris flows, in the vicinity of the affected sites.

Past studies found that this reduced infiltration rate changes over time and the original hydrogeological soil properties are expected to recover in as long as 10 years after the wildfire event, depending on the environmental characteristics and on the soil properties of the site.

Our work aims to investigate the impact of a wildfire on the infiltration conditions of a slope located in the Southern Alps, considering as a case study a wildfire event occurred in Sorico (CO) in December 2018.

The effects of the wildfire on the infiltration rates and the subsequent recovery of the original hydrogeological properties were evaluated over the span of more than two years after the event. Infiltration tests were performed both within the most affected area as well as in the nearest unburnt area. Results were then correlated with precipitation and satellite imagery data in order to retrieve a recovery factor, necessary for the calibration of a simple 1D hydrogeological model.

How to cite: Corti, M., Abbate, A., Ivanov, V., Papini, M., and Longoni, L.: Wildfire impact on the hydrological conditions of an Alpine slope, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-12305, https://doi.org/10.5194/egusphere-egu21-12305, 2021.

There are several different infiltration, overland flow routing, and channel routing schemes that can be used in conjunction with recommended hydrodynamic and infiltration parameter values, which are found within the literature, to provide critical flooding assessments for stakeholders and decision makers.  We focus on post wildfire debris flow and flood analysis in two tributaries of the Snake River in Idaho, Trapper Creek and Rock Creek.  The Badger Fire started on September 12, 2020 in the Sawtooth National Forest in Idaho, USA, and burned sub-alpine fir, lodgepole pine, juniper, mountain brush and grass communities, in the upper part of both the Trapper Creek and Rock Creek watersheds.  Trapper Creek has a U.S. Geological Gaging station, and there are two snow gaging sites available.   The biggest concern for flooding and debris flow is the result of a wintertime rain-on-snow event, which resulted in the largest storm in the gaging record period.    

To estimate runoff in ungaged stream locations, existing process-based hydrodynamic models can be applied in a distributed form to solve the governing equations for mass, momentum and energy in a spatially explicit way. The purpose of this study is to predict potentially inundated land areas as a result of a rain-on-snow event, using the data in the gages basin to provide flood analysis information for both the gaged (Trapper Creek) and ungaged watershed (Rock Creek).  Rain-on-snow events are rainfall events that occur on the snowpack and frozen ground, resulting in a larger magnitude and volume of streamflow.  To predict these flows, Gridded Surface Subsurface Hydrologic Analysis (GSSHA) watershed models are prepared and calibrated to simulate rain-on-snow events in both watersheds.  The runoff generated from a two dimensional overland flow grid is transferred over land with a finite volume numerical method into a one dimensional channel network.  The channel network also uses a finite volume method.    The consistency in the identified range of the parametric values and their physical applicability make GSSHA an ideal candidate for this study, as the model equations provide a methods to evaluate a rain-on-snow event.

How to cite: Turnbull, S., Pradhan, N., and Floyd, I.: Post Wildfire Debris Flow and Flood Analysis of the September 2020 Badger Fire in the Trapper Creek and Rock Creek Watersheds, Idaho, USA., EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-14210, https://doi.org/10.5194/egusphere-egu21-14210, 2021.

Wildfires have become a major concern to society in recent decades because increases in the number and severity of wildfires have negative effects on soil and water resources, especially in headwater areas. Models are typically applied to estimate the potential adverse effects of fire. However, few modeling studies have been conducted for meso-scale catchments, and only a fraction of these studies include transport and deposition of eroded material within the catchment or represent spatial erosion patterns. In this study, we firstly designed the procedure of event-based automatic calibration using PEST, parameters ensemble, and jack-knife cross-validation that is suitable for event-based OpenLISEM calibration and validation, especially in data-scarce burned areas. The calibrated and validated OpenLISEM proved capable of providing reasonable accurate predictions of hydrological responses and sediment yields in this burned catchment. Then the model was applied with design storms of six different return periods (0.2, 0.5, 1, 2, 5, and 10 years) to simulate and evaluate pre- and post-wildfire hydrological and erosion responses at the catchment scale. Our results show rainfall amount and intensity play a more important role than fire occurrence in the catchment water discharge and sediment yields, while fire occurrence is regarded as an important factor for peak water discharge, indicating that high post-fire hydro-sedimentary responses are frequently related to extreme rainfall events. The results also suggest a partial shift from flow to splash erosion after fire, especially for higher return periods, explained by a combination of higher splash erosion in burnt upstream areas with a limited sediment transport capacity of surface runoff, preventing flow erosion in downstream areas. In consequence, the pre-fire erosion risk in the croplands of this catchment is partly shifted to a post-fire erosion risk in upper slope forest and natural areas, especially for storms with lower return periods, although erosion risks in croplands are important both before and after fires. This is relevant, as a shift of sediment sources to burnt areas might lead to downstream contamination even if sediment yields remain small. These findings have significant implications to identify areas for post-wildfire stabilization and rehabilitation, which is particularly important given the predicted increase in the occurrence of fires and extreme rainfall events with climate change.

How to cite: Wu, J., Nunes, J. P., and Baartman, J. E. M.: Testing the impacts of wildfire on hydrological and sediment response using the OpenLISEM model, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-3941, https://doi.org/10.5194/egusphere-egu21-3941, 2021.

Predicting debris yield under post-wildfire conditions is important for hazard mitigation and flood risk planning. Current prediction efforts aim to reduce the amount and impacts of debris flows that minimizes environmental and economic impacts for communities. However, recovery efforts are difficult and costly. Debris flows and excess runoff block access roads and bridges, inhibiting emergency responses. It also effects the surrounding community's water supply and property. Therefore, having a debris flow sediment management plan is crucial. Predicting debris yield volume, estimating debris basin capabilities, and developing yield mitigation alternatives will mitigate future debris yield disasters. In previous versions of the Hydrologic Engineering Center, Hydrologic Modeling System (HEC-HMS) contains no capacity to simulate debris yield. However, the need for debris yield modeling exists throughout the Corps of Engineers, especially mountainous in arid and semi-arid regions. The HEC has added empirical models for prediction debris yield volumes under post-wildfire conditions. The goal is to develop tools within HEC-HMS that provide outputs necessary for developing debris yield mitigation strategies for managing debris yields within the burned watershed. This research discusses the addition of debris yield methods under post-wildfire situations within the watershed available in HEC-HMS 4.5. The new debris yield modeling capabilities will increase the application of HEC-HMS for debris yield modeling studies by directly computing yields from burn watersheds. Additionally, the model was coupled with the Hydrologic Engineering Center, River Analysis System (HEC-RAS) to ensure that debris yield output from HEC-HMS could be easily used as boundary conditions for predicting the hydraulic non-Newtonian debris flow runout and inundation.  The new debris yield methods use precipitation, topography, and soil burn severity information within the watershed to model debris yield. Reach and reservoir debris routing methods are being further developed, meanwhile existing sediment flow routing methods in reach and reservoir elements can be used with certain limitations.

Keywords: Debris Yield Prediction; Post-Wildfire; Hazard Mitigation; Hydrology Modeling System

How to cite: Pak, J., Floyd, I., and Ely, P.: Debris Yield Modeling Application under Post-Wildfire Conditions with the Hydrologic Modeling System (HEC-HMS), EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-494, https://doi.org/10.5194/egusphere-egu21-494, 2021.

Abstract

Wildfires have become an increasing threat for Mediterranean ecosystems, due to increasing climate change induced wildfire activity and changing land management practices. Apart from the initial risk, fire can alter the soil in various ways depending on different fire severities and thus post-fire erosion processes are an important component in assessing wildfires’ negative effects. Recent post-fire erosion (modelling) studies often focus on a short time window and lack the attention for sediment dynamics at larger spatial scales. Yet, these large spatial and temporal scales are fundamental for a better understanding of catchment sediment dynamics and long-term destructive effects of multiple fires on post-fire erosion processes. In this study the landscape evolution model LAPSUS was used to simulate erosion and deposition in the 404 km² Águeda catchment in northern-central Portugal over a 41 year (1979-2020) timespan. To include variation in fire severity and its impact on the soil four burnt severity classes, represented by the difference Normalized Burn Ratio (dNBR), were parameterized. Although model calibration was difficult due to lack of spatial and temporal measured data, the results show that average post-fire net erosion rates were significantly higher in the wildfire scenarios (5.95 ton ha^-1 yr^-1) compared to those of a non-wildfire scenario (0.58 ton ha^-1 yr^-1). Furthermore, erosion values increased with a higher level of burnt severity and multiple fires increased the overall sediment build-up in the catchment, fostering an increase in background sediment yield. Simulated erosion patterns showed great spatial variability with large deposition and erosion rates inside streams. Due to this variability, it was difficult to identify land uses that were most sensitive for post-fire erosion, because some land-uses were located in more erosion-sensitive areas (e.g. streams, gullies) or were more affected by high burnt severity levels than others. Despite these limitations, LAPSUS performed well on addressing spatial sediment processes and has the ability to contribute to pre-fire management strategies. For instance, the percentage soil loss map (i.e. comparison of erosion and soil depth maps) could identify locations at risk.

How to cite: Föllmi, D., Baartman, J., Nunes, J. P., and Benali, A.: A multi-decade assessment of the impact of large fire events on sediment redistribution using LAPSUS - the Águeda catchment, north-central Portugal, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-4615, https://doi.org/10.5194/egusphere-egu21-4615, 2021.

Land use change, as well as changes in the soil physical and chemical properties impact the runoff and erosion generation processes, and overall transport mechanism. Therefore, research and development of a watershed’s physics-based distributed runoff and erosion processes is needed to better predict discharge and erosion under different environments. This is important   for not only local floods and droughts and, geomorphological and landform changes point of view but also for a better understanding of the hydrology, erosion and land surface processes and its impact on ecosystem, transport system, environment and socio-economy and safety. One of the natural and/or manmade causes that brings about changes in land use and soil property is wildfires. In an effort to represent the physics of the watershed under post-fire conditions, this study presents a  detailed analysis of runoff and erosion generation processes, by including soil hydrophobicity and burn severity related soil hydraulic properties changes,  and transport responses, under sediment laden fluid flow conditions, in watersheds under burn conditions.  This study also conducted distributed hydro-geomorphological parameter value identification process for enabling engineers and hydrologists to provide critical post-fire flooding assessments for stakeholders and decision makers in relatively short period.

How to cite: Pradhan, N. R., Floyd, I., Berli, M., Pak, J., Price, M., Turnbull, S., Hobbs, B., Aguilera, F. O. D., Shillito, R., and Giovando, J.: Modelling post-fire runoff and erosion processes for emergency assessment of post-fire flood hazards, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-14028, https://doi.org/10.5194/egusphere-egu21-14028, 2021.

Wildfires are considered to be one of the main causes of soil erosion and land degradation processes in fire-prone areas [1], which are expected to increase in the future because of fire patterns shifting worldwide as a consequence of changes in climate and land use [2]. To maintain the sustainability of ecosystems and protect the values at risk downstream from the fire-affected areas, it is vital to mitigate the increased hydrological and erosive response after fires. Despite soil erosion mitigation treatments have been widely applied after wildfires, their effectiveness has only been assessed in local and regional-scale studies, so the obtained conclusions might be heavily influenced by site-specific conditions.

To overcome this constraint, a meta-analysis was applied on the scientific literature on post-fire soil erosion mitigation treatments indexed in Scopus. The search resulted in 34 publications from which 53 and 222 pairs of treated/untreated observations on post-fire runoff and erosion, respectively, were obtained. The overall effectiveness of mitigation treatments, expressed as effect size, was determined for the runoff and erosion observations, and further analyzed for four different types of treatments (mulching, barriers, seeding, and chemical). The erosion observations concerning mulches were analyzed for differences in effect size between 3 different types of materials (straw, wood, and hydromulch) as well as between different application rates of straw and wood. The erosion observations were also analyzed for the overall effect size of post-fire year, burn severity, rainfall amount and erosivity, and ground cover.

The results showed that all four types of treatments significantly reduced post-fire soil erosion, but that only the mulch and barrier treatments significantly reduced post-fire runoff. From the 3 different mulch treatments, the straw and wood were significantly more efficient in mitigating erosion than the hydromulch. The different straw and wood mulch application rates also influenced their effectiveness. Straw mulch was less effective at rates below than above 200 g m^-2, while mulching with wood at high rates (1300 to 1750 g m^-2) produced more variable outcomes. Results also suggested that the overall effectiveness of the treatments was greatest shortly after fire, in severely burned sites, providing or promoting the development of ground cover over 70%, and with increasing rainfall erosivity.

It can be concluded that, in overall terms, the application of the studied post-fire erosion mitigation treatments represented a better choice than doing nothing, especially in sites where erosion is high. However, works on this topic are underrepresented outside of the USA, Spain and Portugal. Most of the studies were conducted at hillslope scale and tested mulching and/or barriers, while larger scales and other treatments were neglected. Further efforts are needed in testing, from field and modelling experiments, combinations of existing and/or emerging erosion mitigation treatments to ensure that the most suitable measures are applied after fires.

[1] Shakesby (2011). Earth-Sci. Revs. 105:71-100. DOI: 10.1016/j.earscirev.2011.01.001

[2] Andela et al. (2017). Science 356: 1356-1362. DOI: 10.1126/science.aal4108

How to cite: Girona-García, A., Vieira, D., Silva, J., Fernández, C., Robichaud, P., and Keizer, J.: A meta-analysis on the effectiveness of post-fire soil erosion mitigation treatments, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-3097, https://doi.org/10.5194/egusphere-egu21-3097, 2021.

Recently burnt areas across the world have been documented to produce strong to extreme erosion responses but these responses are much better quantified for (micro-)plots and planar hillslopes than for convergent hillslopes and catchments. The same applies, mutatis mutandis, for the effectiveness of so-called emergency stabilization measures to reduce the risks of such strong to extreme responses. The only prior study in Portugal on the mitigation of post-fire erosion beyond the planar slope scale (i.e. swales of 500-800 m2) tested mulching with eucalypt logging residues. It found the treatment to be highly effective during the first two post-fire hydrological years in the sense that soil losses were, average, 88 and 77% smaller at the three mulched swales than at the 3 untreated swales. This in spite the mulch had been applied at reduced rate (2.4 Mg ha-1) compared to preceding, plot-scale studies in the region (>8 Mg ha-1). Against this background, the present study decided to test the effectiveness of log barriers to reduce post-fire erosion beyond the planar slope scale, in particular to provide evidence supporting the post-fire land management strategy that is being developed by the INTERREG-SUDOE project EPyRIS (SOE2/P5/E0811). The study area is located in the Aveiro District of central Portugal and burnt during early  September 2020. In the part of the burnt area that is being managed by the Portuguese Nature Conservation and Forests Institute (ICNF), three pairs of neighbouring micro-catchments of 0.3-0.8 ha and, in one exceptional case (due to run-on from a forest track), 2.7 ha were instrumented with sediment fences at their outlets before the occurrence of the first significant rainfall event after the wildfire. The barriers, however, could not be installed until after the subtropical storm ALPHA that hit continental Portugal on 18-19 September, also due to some delay in the contracting of a company that would have prior experience in implementing post-fire emergency stabilization measures. The sediment yields produced by this first post-fire rainfall event were used to select which of each pair of micro-catchments to be treated, i.e. the one producing most erosion. Furthermore, the initial sediment yields of the three to-be-treated micro-catchments were used to decide the number of barriers per catchment, ranging from one to three. Both these aspects of the experimental design imply that the quantification of (cost-)effectiveness will less straightforward than in case of a randomized design. In compensation, the upslope part of each barrier was covered with geotextile immediately after construction to estimate the barrier’s capacity to induce sediment deposition and, at the scale of the entire micro-catchment, its effectiveness to reduce post-fire sediment yields, even if sediment deposition will only be measured at the end of each hydrological. This envisaged poster will present the differences in sediment yields between the paired, treated and untreated micro-catchments during the first post-fire autumn-winter period, and discuss them in function of terrain characteristics of the micro-catchments, RS-based fire severity, rainfall regime and changes in surface cover as derived from RGB imagery acquired with a low-cost drone.

How to cite: Keizer, J. J., Silva, J., Augustijn, M., Martins, R., Martins, M., Basso, M., Girona-García, A., Simões, L., and Vieira, D.: Mitigation of post-fire erosion from terraced micro-catchments using timber barriers, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-13677, https://doi.org/10.5194/egusphere-egu21-13677, 2021.

The extensive afforestation of the Mediterranean rim of Europe in recent decades has increased the number of wildfire disturbances on hydrological and sediment processes, but the impacts on headwater catchments is still poorly understood, especially when compared with the previous agricultural landscape. This work monitored an agroforestry catchment in the north-western Iberian Peninsula, with plantation forests mixed with traditional agriculture using soil conservation practices, for one year before the fire and for three years afterwards, during which period the burnt area was plowed and reforested. During this period, continuous data was collected for meteorology, streamflow and sediment concentration at the outlet, erosion features were mapped and measured after major rainfall events, and channel sediment dynamics were monitored downstream from the agricultural and the burnt forest area. Data from 202 rainfall events with over 10 mm was analysed in detail.

Results show that the fire led to a notable impact on sediment processes during the first two post-fire years, but not on streamflow processes; this despite the small size of the burnt area (10% of the catchment) and the occurrence of a severe drought in the first year after the fire. During this period, soil loss at the burnt forest slopes was much larger than that at most traditionally managed fields, and, ultimately, led to sediment exhaustion. At the catchment scale, storm characteristics were the dominant factor behind streamflow and sediment yield both before and after the fire. However, the data indicated a shift from detachment-limited sediment yield before the fire, to transport-limited sediment yield afterwards, with important increases in streamflow sediment concentration. This indicates that even small fires can temporarily change sediment processes in agroforestry catchments, with potential negative consequences for downstream water quality.

How to cite: Nunes, J. P., Bernard-Jannin, L., Rodríguez-Blanco, M. L., Boulet, A.-K., Santos, J. M., and Keizer, J. J.: Impacts of wildfire and post-fire land management on hydrological and sediment processes in a humid Mediterranean headwater catchment, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-4436, https://doi.org/10.5194/egusphere-egu21-4436, 2021.

As in any other Mediterranean region, wildfires highly affect Portuguese forests leading to substantial economic and ecological losses. Wildfires are also an important cause for the degradation of forest ecosystem services, which are responsible for the maintenance of water quality, flooding and soil erosion control. Considering that wildfire frequency is expected to increase in the future due to changes in climate and socio-economic drivers, future land degradation cause by wildfires is considered with great concern.

To tackle the impacts of wildfires on the affected ecosystems such as soil erosion is highly recommendable the use of adequate post-fire management practices for its mitigation. However, the dimension of the area affected by the 2017 wildfires in Portugal (500 thousand ha) showed the impossibility to effectively treat a nation-wide burned area for erosion control. Given this context, hydrological modelling arises as a key–tool for post-fire land management decision making, by identifying potential on-and-off-site post-fire impacts, and by allowing the selection of target areas with a higher soil erosion risk for the implementation of mitigation treatments.

To address this problem, the ESP team - under the FEMME project - defined the strategy of using soil erosion models at hillslope scale to address on-site impacts at the national level and catchment scale models to address off-site impacts. A national soil erosion risk map in case of a wildfire will help land managers to choose the priority areas for the implementation of emergency stabilization measures. While continuous and event-based hydrological models, will allow assessing the risks of water quality degradation and the occurrence of extreme hydrological events, which can impact downstream values-at-risk.

To understand if the chosen model approach is adequate to the problem in hand since it resulted in outputs with distinct spatial and temporal scales, we have decided to perform an evaluation focused on scales and model adaptations to burned areas. We were able to conclude that simple empirical models such as the Morgan-Morgan-Finney [1], which can provide predictions at hillslope and seasonal-to-annual scale, are well adapted to post-fire conditions and are useful to identify high risk areas for the implementation of mitigation treatments. On the other side, their simplicity does not allow to determine the risk of flooding or water bodies contamination, outside the burned area, and under specific rainfall events which implies a daily or sub-daily time-steps. For that purpose, spatially-explicit process-based such as SWAT [2] or LISEM [3] can provide a more detailed feedback, although there have been few model adaptations to burned conditions at this scale, especially considering the implementation of post-fire mitigation measures.

[1] Morgan, R., 2001. A simple approach to soil loss prediction: a revised Morgan–Morgan–Finney model. Catena 44 (4): 305–322. https://doi.org/10.1016/S0341-8162(00)00171-5

[2] Arnold, J.G., Fohrer, N., 2005. SWAT2000: Current capabilities and research opportunities in applied watershed modelling. Hydrol. Process. 19, 563–572. https://doi.org/10.1002/hyp.5611

[3] De Roo APJ, Wesseling CG, Ritsema CJ (1996) LISEM: a single‐event physically based hydrological and soil erosion model for drainage basins. I: theory, input and output. Hydrological processes 10, 1107–1117.

How to cite: Vieira, D., Parente, J., Basso, M., Lopes, A., and Girona-García, A.: Tackling post-fire impacts and their mitigation by modelling hydrological processes at different scales in Portugal, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-3182, https://doi.org/10.5194/egusphere-egu21-3182, 2021.