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When the smoke clears: predicting and preventing catastrophic erosion and flooding after wildfires in volcanic terrains

Periodic Reporting for period 1 - FireAndRiskPrevention (When the smoke clears: predicting and preventing catastrophic erosion and flooding after wildfires in volcanic terrains)

Reporting period: 2015-08-01 to 2017-07-31

Wildfires remove protective vegetation, produce ash with high content in potential pollutants, and enhance runoff processes, leaving the landscapes vulnerable to catastrophic flood, erosion and water contamination events. The resulting losses and costs of the actions taken to reduce risks to population and infrastructures, or to restore ecosystem functions following wildfires have increased dramatically in the last 30 years. For example, in the USA mitigation costs have increased from $6.3 M. in the 1970s to $188 M. in the 2000s (no data have been published for the EU).
Major advances have been made in the last decade to support land managers: (i) models to anticipate runoff and erosion events in the post-fire period, such as the Water Erosion Prediction Project model (WEPP, US Forest Service); and (ii) innovative hillslope stabilization treatments aimed at reducing runoff occurrence and erosion events.
Although widespread in the USA, the application of these advances is still in its infancy Europe due to the lack of region- and soil-specific calibration and effectiveness testing, leading in some cases to a risk to lives and resources in particularly vulnerable areas. Population and infrastructure in volcanic regions are usually extremely vulnerable to hydrological and erosional events due to their location in, or downstream of, fire-prone steep slopes, high population density, and the general instability of volcanic terrain. For example, in 2009 a severe erosion event occurred in a fire-affected area in volcanic terrain in La Palma (Canary Islands, Spain) that led to damages to infrastructure (€5 M.) and affected public safety during the first rainstorm after the fire. The lack of adapted models to predict runoff, erosion, and ash transport and knowledge on the effectiveness of post-fire mitigation treatments hinders the ability of managers to predict catastrophic events and protect human lives, infrastructure, and ecosystem services.
This project aimed to fill these knowledge and management gaps by using an innovative field, laboratory, and modelling approach and a carefully chosen implementation programme, involving global leaders in academia, industry and management. This successful collaboration resulted in (i) the validation and calibration of the WEPP model for the volcanic soils of the Canary Islands (Spain), (ii) the evaluation of the effectiveness of three alternative and innovative hillslope stabilization treatments for this terrain type, and (iii) the development of a model prototype to predict ash transport and contamination risk to water bodies.
The main objective of this proposal was to provide land managers from volcanic areas with a tool to predict the risk of occurrence of catastrophic runoff and erosion events. After a hands-on training course with Drs. Elliot and Robichaud (US Forest Service) we started to collect data on the hydrological and erosional response of fire-affected volcanic soils in the volcanic island of Tenerife (Spain). The data obtained enable us to calibrate and validate the WEPP model to the particularities of the volcanic soils of the island. This output has been transferred to land managers of the island for its use to plan post-fire mitigation actions based on this information.
The effectiveness of four hillslope stabilization treatments was compared for the first time for this terrain type: (i) log erosion barriers, the most common treatment currently used in the Canary Islands and in Spain; (ii) wood shred mulch, a novel method extensively used in USA but not tested for volcanic soils to date; (iii) pine needle mulch, a cheaper alternative to the wood-based mulches due to its lower density and transport costs; and (iv) polyacrylamide (PAM) a synthetic polymer extensively used in agriculture to stabilize degraded soils but not tested in fire-affected volcanic soils. The comparison provided critical knowledge from a management perspective since log erosion barriers and PAM provide limited effect in reducing runoff and erosion processes, whereas pine needle and wood shred mulches showed similarly high efficiency in reducing runoff and erosion. These results have been already transferred to Cabildo de Tenerife and we expect that this impact can be exported to other areas in volcanic terrain.
To address the critical knowledge and management gap regarding the impact of ash on water quality, we have developed the first conceptual model able to predict ash delivery risk and calculate the probability of occurrence of ash contamination events in fire-affected environments. The prototype model, designed in collaboration with Drs. Elliot and Robichaud (US Forest Service), has already been successfully tested using laboratory data. The prototype is now ready to be calibrated and validated for “real life” conditions using field data from key vulnerable ecosystems before being transferred to end-users. This ambitious objective is my next step in research through a recently funded 3-years project and will help me to definitively consolidate my position in science gained through this Marie Skłodowska-Curie fellowship.
This ambitious project has enabled me to achieve unprecedent results in the field of predicting and mitigating runoff, erosion, and contamination risks in fire-affected soils. From a societal perspective, the combined use of the successfully adapted WEPP model and the most effective hillslope stabilization treatments for volcanic terrain will lead to a more effective protection of human live and non-market cultural and ecological values. The result will be preventing the occurrence of catastrophic events such as the recent mudflows in California (January 2018) triggered by the combined effect of fire and rainstorms that sadly killed 20 people and destroyed many roads and buildings. From an economic perspective, the combined use of this knowledge, identifying the most vulnerable areas using WEPP and implementing the most effective treatments, will turn into average savings of €5 Mill. per year for the Canary Islands alone when compared to previous restoration procedures (figures calculated using economic estimations from the USA). Additionally, pine needle harvesting and production of wood shreds for livestock or agricultural use are stablished economic activities in some regions of the world. Thus, their use as hillslope stabilization treatments can promote the regional economy.
The ash transport model prototype we have developed through this project is the first of its type able to predict the probability of ash delivery and contamination risk in the post-fire period. This tool will have a direct impact on society by supporting managers in protecting water reservoirs located in fire-prone or fire-managed areas that, for example, supply 60% of the fresh-water to the 100 biggest cities in the world. Previous contamination events by ash led to expensive treatment expenses exceeding €22 Mill. in Denver (USA; 1996&2002), €25 Mill. in Canberra (Australia; 2003), and €4 Mill. in Belfast (UK; 2011). The model will support water-supply managers in designing, for example: (i) prescribed burn plans and silvicultural activities to reduce potential ash production in vulnerable locations; (ii) post-fire mitigation plans aimed at identifying critical sources of ash and implement actions to stabilize ash in critical areas; and (iii) emergency water treatment procedures to decontaminate water.
Dr. Jonay Neris collecting ash samples supported by US Forest Service at RedFord Canyon Fire (USA)
Dr. Jesus Notario (Universidad de La Laguna) applying a wood chip mulch at Candelaria (Spain)
Helicopter filling the bucket during the Thompson Falls fire (WA)
Performing rill simulations suported by Cabildo de Tenerife staff at Vilaflor (Spain)
Soil moisture data collection at Candelaria (Spain)
Prof. Stefan Doerr (Swansea University) during the rainfall simulations (Vilaflor, Spain)
Working in the Rim Fire with Dr. Robichaud and his crew
Silt fences installation by Cabildo de Tenerife staff at Candelaria (Spain)
Ash sampling with Dr. Elliot (US Forest Service)
Seed selection to be covered by waterproof coat
Silt fences collecting runoff during the storm in Oct 2015 (Vilaflor, Spain)
Installation of log barriers by Cabildo de Tenerife staff at Vilaflor (Spain)
Dr. Robichaud (US Forest Service) collecting ash samples at RedFord C
Dr. Marcos Lado (Universidade de A Coruna) during the soil sampling at Vilaflor (Spain)
Rainfall simulation plot covered by wood chips at Vilaflor (Spain)