Forest fire danger rating in complex topography – results from a case study in the Bavarian Alps in autumn 2011

Abstract

Abstract. Forest fire danger rating based on sparse meteorological stations is known to be potentially misleading when assigned to larger areas of complex topography. This case study examines several fire danger indices based on data from two meteorological stations at different elevations during a major drought period. This drought was caused by a persistent high pressure system, inducing a pronounced temperature inversion and its associated thermal belt with much warmer, dryer conditions in intermediate elevations. Thus, a massive drying of fuels, leading to higher fire danger levels, and multiple fire occurrences at mid-slope positions were contrasted by moderate fire danger especially in the valleys. The ability of fire danger indices to resolve this situation was studied based on a comparison with the actual fire danger as determined from expert observations, fire occurrences and fuel moisture measurements. The results revealed that, during temperature inversion, differences in daily cycles of meteorological parameters influence fire danger and that these are not resolved by standard meteorological stations and fire danger indices (calculated on a once-a-day basis). Additional stations in higher locations or high-resolution meteorological models combined with fire danger indices accepting at least hourly input data may allow reasonable fire danger calculations under these circumstances.

Influence of extreme climate conditions on the forest fire risk in the Timočka Krajina region (northeastern Serbia)

“…• when I ≤ 2.0, fire occurrence was very likely. Although the Angström index is a simple day-to-day fire danger indicator, it was successfully applied for different regions in the central part of Europe: Slovakia (Skvarenina et al, 2003), southern Germany (Schunk et al, 2013), Austria (Arpaci et al, 2013), Serbia (Lukić et al, 2017), etc. The Angström index might be a good indicator if there are rapid changes in weather situations, which increase the fire danger situation so quickly, that fuel or soil moisture models are not able to capture that moment (Arpaci et al, 2013).…”

Fire Danger Observed from Space

“…What is more, the aspect of the terrain will also influence the fuel moisture conditions, as a slope facing south (in the northern hemisphere) will receive more solar radiation and increase the drying of the fuels (Holden and Jolly 2011). Topography will also indirectly affect fire danger influencing other variables such as the distribution of the fuels, wind behaviour, and differences in temperature, relative humidity, and precipitation due to elevation (Schunk et al 2013).…”

Unusual late-fall wildfire in a pre-Alpine Fagus sylvatica forest reduced fine roots in the shallower soil layer and shifted very fine-root growth to deeper soil depth

“…Although wildfire in Europe is usually associated with the fire-prone countries surrounding the Mediterranean Sea, the alpine region of Central Europe experiences wildfires of relatively low frequency, intensity, and size that mostly (~ 90%) occur on southern slopes of the Alps 18 – 20 . Historically, these fires occurred either in early spring (March and April) or summer (July and August) 21 . A long-term analysis (1951–2010) of indices of forest fire danger and ten years of observed forest fires (2001–2010) revealed a significant increase in the western Alps and an even stronger increase in the southern Alps 22 , and fire regimes are expected to react dynamically to alterations in the climate–weather–fuel system with changes in fire intensity, seasonality, frequency, and scale 23 , 24 .…”

“…A long-term analysis (1951–2010) of indices of forest fire danger and ten years of observed forest fires (2001–2010) revealed a significant increase in the western Alps and an even stronger increase in the southern Alps 22 , and fire regimes are expected to react dynamically to alterations in the climate–weather–fuel system with changes in fire intensity, seasonality, frequency, and scale 23 , 24 . Indeed, extraordinary changes in alpine fire regimes have been observed 25 , often associated with temporal climate variability 26 – 28 , and especially with heat waves and dry foehn winds, which are generally regarded as an indication of a changing climate that will lead to new fire regimes in the Alps 21 , 29 , 30 .…”