Post-fire Soil Erosion

Post-fire soil erosion in Europe is long lasting and burned soils require attention

We use an integrated approach combining soil erosion modelling with RUSLE, post-fire remote sensed data, and revision of the literature in order to assess the impact of the 2017 wildfires in Europe for the following 5 years. Results show that despite the initially expected increase in soil erosion, the recovery of such erosion rates until the background levels was not achieved during the 5 years assessment. Moreover, by the end of the study period 46% still presented vegetation cover levels bellow the pre-fire conditions, somehow explained by a reduced natural recovery, but also by additional impacts from post-fire land management actions such as logging, or the occurrence of other wildfires in the same location. Despite its reduced operationalization in Europe, the application of post-fire mitigation measures could attenuate 63-77% of the soil erosion impacts.

Fig. 1. Overall methodological modelling approach.

Main highlights

• Sharp increase in the soil erosion was found after wildfire (11.8-fold).
• No full recovery was found after the 5-years assessment.
• After 5 years, 46% of the burned area presented vegetation cover lower than the pre-fire.
• Post-fire mitigation has the potential to reduce post-fire soil erosion impacts by 63–77%.

Fig. 2. Post-fire soil erosion estimations averaged by 25 × 25 km grid for EU and UK, for the first year following the 2017 wildfires, and location of the reference sites Pedrógão Grande for Portugal, Attica for Greece, and Enna for Italy.

Summary

Annually, millions of hectares of land are affected by wildfires worldwide, disrupting ecosystems functioning by affecting on-site vegetation, soil, and above- and belowground biodiversity, but also triggering erosive off-site impacts such as water-bodies contamination or mudflows. Here, we present a soil erosion assessment following the 2017’s wildfires at the European scale, including an analysis of vegetation recovery and soil erosion mitigation potential. Results indicate a sharp increase in soil losses with 19.4 million Mg additional erosion in the first post-fire year when compared to unburned conditions. Over five years, 44 million Mg additional soil losses were estimated, and 46% of the burned area presented no signs of full recovery. Post-fire mitigation could attenuate these impacts by 63-77%, reducing soil erosion to background levels by the 4th post-fire year. Our insights may help identifying target policies to reduce land degradation, as identified in the European Union Soil, Forest, and Biodiversity strategies.

Conclusions

This is the first study that assesses soil erosion in post-fire conditions at the European scale following the 2017 wildfires. By adapting the RUSLE model to consider post-fire impacts in function of burn severity, and vegetation recovery for forests, grasslands, and shrubland, the Pan-European Soil Erosion assessment was updated with an additional source of soil erosion. Moreover, this work also assesses the current post-fire erosion and vegetation recovery dynamics, and the potential mitigation of such impacts if appropriate forest management actions take place. The principal findings of this modelling exercise with respect to the 2017 EU burned area are as follows:

• a sharp increase in the soil erosion estimations was found after wildfire (11.8-fold), representing an addition of 2% (19.4 million Mg) to the reference soil erosion for EU, for the first post-fire year alone, despite represents only 0.2% of the area;
• a full recovery of the soil erosion rates to the background levels was not observed within the study period, as also evidenced by the 46% of the burned area with vegetation cover lower than the pre-fire;
• post-fire natural recovery was affected by post-fire land management operations, and high fire recurrence;
• post-fire mitigation has the potential to reduce post-fire soil erosion impacts by 63–77% in the first year, and allow a reduction in soil erosion to the background levels by the 4th post fire year.

The results of this assessment evidence that not sufficient attention has been given to the mitigation of wildfire impacts given the importance of forest soils for the ecosystems services provision. Moreover, the new climate demands evidence the urgent improvement of EU's forest resilience and adaptation to climate change, in order also to halt land degradation in forest soils.

Data and additional material

The soil erosion data mapping post-fire soil erosion in EU and UK following the 2017’s wildfires during 5 post-fire years is provided. Five maps (GeoTIFF) and their corresponding dataframe (Rdata) are provided at 25m resolution, from year 1 (2017) to year 5 (2021).

Download the data

Reference:

Vieira, D.C.S., Borrelli, P., Jahanianfard, D., Benali, A., Scarpa, S. and Panagos, P., 2023. Wildfires in Europe: Burned soils require attention. Environmental research, 217, Art. No. 114936.

More studies on post-fire erosion

Study aims to assess the impact of the Mati, Attika (Greece) wildfire on soil erosion.The event caused 102 fatalities, inducing severe consequences to the local infrastructure network; economy; and natural resources. As such, the Revised Universal Soil Loss Equation (RUSLE) was implemented (pre-; post-fire) at the Rafina, Attika watershed encompassing the Mati. Fire severity was evaluated based on the Normalized Burn Ratio (NBR). This index was developed utilizing innovative remotely sensed Earth Observation data (Sentinel-2). The high post-fire values indicate the fire's devastating effects on vegetation loss and soil erosion.

Reference: Efthimiou, N., Psomiadis, E. and Panagos, P., 2020. Fire severity and soil erosion susceptibility mapping using multi-temporal Earth Observation data: The case of Mati fatal wildfire in Eastern Attica, Greece. Catena, 187, art.no 104320.

Post-fire soil erosion risk assessment in Portugal. A post-fire soil erosion risk map for the forest and shrubland areas in mainland Portugal and assess its reliability. To this end, the semi-empirical Morgan–Morgan–Finney erosion model was used to assess the potential post-fire soil erosion according to distinct burn severity and climate scenarios, and the accuracy of the predictions was verified by an uncertainty analysis and validated against independent field datasets.

Reference: Parente, J., Girona-García, A., Lopes, A.R., Keizer, J.J. and Vieira, D.C.S., 2022. Prediction, validation, and uncertainties of a nation-wide post-fire soil erosion risk assessment in Portugal. Scientific Reports, 12(1)