High-resolution modeling of historical forest fires in the Canton of Bern

Abstract

Forest fires are considered an important hazard in forested areas and a serious threat to forest ecosystem and buildings. The combination of drought, high temperatures, and wind increases the risk of forest fires. To better understand the fundamental causes and consequences of fire, we need to study the historical fire regimes. In this study, the meteorological conditions were simulated with the WRF model (Weather Research and Forecasting; Skamarock et al. 2008) for three historical forest fires, in the Canton of Bern, Switzerland (La Neuveville, April 1893, Simmenflueh, August 1911, Kirchberg, April 1915). In terms of area, these are the largest fires in the canton of Bern in the Swiss fire database. The "Twentieth Century Reanalysis" version 3 (20CRv3, Slivinski et al. 2019) was used as a boundary condition. 20CRv3 has a spatial resolution of about 75 km and a temporal resolution of three hours. Using WRF version 4.1.2 20CRv3 has now been gradually downscaled to a resolution of 1x1 km^2. Simulations suggest that the soil had dried out in the previous week and soil moisture had reached low values on the day the fire broke out. High-resolution fire weather indices are also calculated. A lack of precipitation and high temperatures led to high forest fire index values and a high to very high risk of forest fires. References[1] Slivinski, L. C.et al. (2019), Towards a more reliable historical reanalysis: Improvements to theTwentieth Century Reanalysis system. , Q. J. Roy. Meteorol. Soc. 145, 2876-2908.[2] Pfister, L. , S. Brönnimann, M. Schwander , FA Isotta , P. Horton, and C. Rohr, (2020) StatisticalReconstruction of Daily Precipitation and Temperature Fields in Switzerland back to 1864, Clim.past 16, 663-678.[3] Skamarock, WC, et al. (2008) A Description of The Advanced Research WRF Version 3. NCARTechnical Note.[4] Van Wagner, C.E. (1987): Development and Structure of the Canadian Forest Fire Weather IndexSystem, Forestry Technical Report, Canadian Forestry Service Headquarters, Ottawa.