A phenology-driven fire danger index for northern grasslands

Johan Sjöström; Anders Granström

doi:10.1071/WF23013

RESEARCH ARTICLE (Open Access)

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A phenology-driven fire danger index for northern grasslands

Johan Sjöström

^A ^* and Anders Granström

^B

+ Author Affiliations

- Author Affiliations

^A Department of Fire and Safety, RISE Research Institutes of Sweden, Box 857, 501 15 Borås, Sweden.

^B Department of Forest Ecology and Management, Swedish University of Agricultural Sciences, 901 83, Umeå, Sweden. Email: anders.granstrom@slu.se

^* Correspondence to: johan.sjostrom@ri.se

International Journal of Wildland Fire 32(9) 1332-1346 https://doi.org/10.1071/WF23013

Submitted: 30 January 2023 Accepted: 8 July 2023 Published: 31 July 2023

© 2023 The Author(s) (or their employer(s)). Published by CSIRO Publishing on behalf of IAWF. This is an open access article distributed under the Creative Commons Attribution-NonCommercial-NoDerivatives 4.0 International License (CC BY-NC-ND)

Abstract

Background

Directly after snowmelt, northern grasslands typically have highly flammable fuel-beds consisting of 100% grass litter. With green-up, the addition of high-moisture foliage leads to progressively decreasing fire hazard.

Aims

Our aim was to create a fire-danger index for northern grasslands that incorporated grass phenology.

Methods

We made use of 25 years of Swedish wildfire data and 56 experimental fires conducted during one full fire-season, merged with established models for moisture content and flame spread rates. Refined data on equilibrium moisture content of grass litter were obtained through laboratory tests.

Key results

The RING (Rate of spread In Northern Grasslands) model uses cumulative air temperature as a proxy for growing season progression. Three independent functions account for impact of wind, moisture content and the damping effect of live grass, respectively. The latter results in exponentially decaying rate of spread (ROS) with the progressing season. Following the field experiments, green grass proportion as low as 10–20% (live/dead dry-mass) resulted in model-ROS so reduced that the grassland fire season could effectively be considered over.

Conclusions

The model, calculated from standard meteorological data only, matches the experimental results and separately performed validation tests, as well as wildfire dispatch data.

Implications

RING has been used in Sweden since 2021 and is likely applicable to other northern regions as well.

Keywords: ecosystems, boreal, fire behaviour, northern grasslands, phenology, propagation, fire danger, fuel, wildland–urban interface.

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