A multisensor and multitemporal approach to assess wildfire occurrence and landscape disturbance at Marsden Moor Estate, West Yorkshire.

UK peatlands are of great environmental importance, they are a major carbon store locking-in approximately 3.2 billion tonnes of carbon and cover 12% of UK land area (CEH, 2021). Wildfire disturbance in UK peatlands is of growing concern. The European Forest Fire Information System (EFFIS) reported 111 burned areas for the UK in 2019 burning a total of 28,754 hectares. This is the highest total area burnt since EFFIS burned area monitoring began in 2008 with the fire season of 2018 providing the second highest record of area burnt, totalling 18,472 hectares.

This research is part of the Natural Environment Research Council (NERC) funded project “Towards a UK fire danger rating system: Understanding fuels, fire behaviour and impacts” (https://ukfdrs.com/). Work package 1 focuses on the use of Earth Observation techniques to assess (a) the spatial distribution of vegetation fuel-loads across the UK and (b) to develop a dynamic fuel map based on seasonal change and land cover management in the South Pennines, England. This research provides some initial investigation of wildfire occurrence and landscape disturbance for the Marsden Moor Estate in the South Pennines from 2019 - 2021.

The Marsden Moor Estate owned by the National Trust in West Yorkshire, UK, is a Site of Special Scientific Interest (SSSI), a Special Area of Conservation (SAC) and Special Protection Area (JNCC, 2021) (https://sac.jncc.gov.uk/site/UK0030280). This blanket bog habitat is home to rare upland species such as the mountain hare and red listed Birds of Conservation Concern 4 (BoCC4) such as the lapwing, skylark and the curlew (British Trust for Ornithology, 2021). Since 2019, the National Trust reported a total of £700,000 worth of damage caused by wildfires on the Marsden Moor Estate (National Trust, 2021). Over the past three years there have been large wildfire events (26 February 2019, 22 April 2019, 23 March 2020 and 25 April 2021) with the biggest fire in April 2019 with a reported 700 hectares of peatland damaged degrading this fragile landscape (National Trust, 2021).

This paper presents a multisensor and multitemporal approach to monitor wildfire occurrence and to assess the impact of these events at the landscape scale at Marsden Moor. We examined (a) the hydrological and topographic characteristics of the estate and (b) the dynamics of vegetation conditions during 2019 – 2021. The estate had a 0.5m spatial resolution LiDAR survey commissioned in 2013 but there was limited onsite knowledge of how to process this data and create derived hydrological and topographic products. The hydrological and topographic assessment used LiDAR derived products for obtaining slope, aspect and a Topographic Wetness Index (Beven and Kirkby, 1979). The Topographic Wetness Index was important in spatially mapping drier v's wetter areas across the peatland, with drier areas potentially being areas of degradation. Previous to this work, there was no multitemporal analysis of vegetation greenness, vegetation stress and regular mapping of areas of bare ground for the estate. Landsat 8 Operational Land Imager (OLI) and Sentinel-2A/-2B data were used to quantify the total area burnt from 2019 – 2021. Furthermore, these optical sensors were analysed to assess land cover dynamics and to assess post-fire vegetation recovery using spectral indices e.g. Normalised Burn Ratio (NBR), Bare Soil Index (BSI), Enhanced Vegetation Index and Normalised Vegetation Index (NDVI).

Vision-1 four-band (visible and near-infrared channel) multispectral 3.5m and panchromatic 0.87m data was acquired by Airbus UK Satellite Services Operations Team on 31 July 2020 and 8 November 2021. The Vision-1 data was atmospherically corrected using ENVI Quick Atmospheric Correction (QUAC) tool with NDVI and EVI spectral indices generated. The Vision-1 acquisitions provided a unique opportunity to generate 3.5m resolution NDVI and EVI maps to compare with the medium resolution Sentinel-2 and Landsat 8 OLI time series. The Vision-1 data enables a more detailed assessment of the Marsden Moor landscape to check if any subtle differences in vegetation greenness are visible especially for areas previously burnt which may not be possible with the Sentinel-2 and Landsat 8 OLI data.

These research outputs will support peatland restoration decision making at the Marsden Moor Estate by identifying areas of vegetation stress and understanding where dry areas are located across the estate which could benefit from peatland rewetting interventions e.g. installation of timber dams and sphagnum moss plug planting. In addition, the estate will gain a more comprehensive understanding of