Dynamic fuel mapping in the South Pennines using a multitemporal intensity and coherence approach

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).

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 focuses on (b) the dynamic fuel map.

The South Pennines covers the Peak District National Park (PDNP) which is the oldest national park in the UK and extends further north to Marsden Moor. The Marsden Moor Estate owned by the National Trust in West Yorkshire, 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). The South Pennines 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 skylark, curlew and lapwing (British Trust for Ornithology, 2021).

Wildfire disturbance in UK peatlands is of growing concern for example 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 at Marsden Moor (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 impacting this fragile landscape (National Trust, 2021). Regular wildfire activity extends throughout the South Pennines region as recorded by Incident Recording System (IRS) data provided to the UKFDRS Project by the Home Office.

This paper presents a SAR intensity and InSAR coherence multitemporal approach to monitor wildfire occurrence and to assess the impact of these events at the landscape scale for the South Pennines area. Fuel properties of peatland vegetation in the South Pennines vary spatially due to variation in land management activites/wildfire occurrence and also seasonally due to phenological change. We examined the dynamics of land cover types from 2017 – 2023 using a Sentinel-1A and -1B intensity time series for both VV and VH polarisations. Structural changes of the vegetation types is analysed using InSAR coherence. This work extends previous SAR intensity and InSAR coherence analysis reported by Millin-Chalabi (2015) using ERS-2, Envisat ASAR and ALOS PALSAR data in the PDNP.

The latest 10m land cover map from the Centre for Ecology and Hydrology is used to implement a stratified sampling technique for extracting intensity and coherence values for key land cover types e.g. bog, heather, heather grassland and acid grassland. Other environmental variable will be taken into consideration when sampling e.g. precipitation. topography and burn severity. Areas unburnt will also be sampled to act as a control and mode of comparison to burned areas (supplied by Moors for the Future Partnership).

The outcomes of this work will be combined in the future with dynamic fuel map analysis using optical sensors led by Labenski (2023) to provide a detailed understanding of the wildfire regime and potential wildfire risk for the South Pennines region.