Long-term temporal changes in the occurrence of a high forest fire danger in Finland

H M Mäkelä,M Laapas,A Venäläinen

doi:10.5194/nhess-12-2591-2012

H M Mäkelä, M Laapas + Show 1 more

Open Access

https://doi.org/10.5194/nhess-12-2591-2012

Copy DOI

Abstract

Abstract. Climate variation and change influence several ecosystem components including forest fires. To examine long-term temporal variations of forest fire danger, a fire danger day (FDD) model was developed. Using mean temperature and total precipitation of the Finnish wildfire season (June–August), the model describes the climatological preconditions of fire occurrence and gives the number of fire danger days during the same time period. The performance of the model varied between different regions in Finland being best in south and west. In the study period 1908–2011, the year-to-year variation of FDD was large and no significant increasing or decreasing tendencies could be found. Negative slopes of linear regression lines for FDD could be explained by the simultaneous, mostly not significant increases in precipitation. Years with the largest wildfires did not stand out from the FDD time series. This indicates that intra-seasonal variations of FDD enable occurrence of large-scale fires, despite the whole season's fire danger is on an average level. Based on available monthly climate data, it is possible to estimate the general fire conditions of a summer. However, more detailed input data about weather conditions, land use, prevailing forestry conventions and socio-economical factors would be needed to gain more specific information about a season's fire risk.

Highlights

A forest fire is a consequence of three elements: suitable weather conditions, flammable fuel load and an igniter (e.g. Pyne, 2001)
Using mean temperature and total precipitation of the Finnish wildfire season (June–August), the model describes the climatological preconditions of fire occurrence and gives the number of fire danger days during the same time period
The main objective of this study is to examine the longterm temporal variation of forest fire danger in Finland with emphasis on the extreme fire danger conditions

Summary

Introduction

A forest fire is a consequence of three elements: suitable weather conditions, flammable fuel load and an igniter (e.g. Pyne, 2001). A forest fire is a consequence of three elements: suitable weather conditions, flammable fuel load and an igniter Fire in boreal forests is typically human-ignited and the other main cause is a lightning strike (Wallenius, 2008). Fire has traditionally been an important natural factor contributing to the development and structure of the northern boreal forests Weather and climate play a critical role in setting the conditions favourable for a forest fire. High temperatures and low relative humidities combined with strong wind intensify evaporation, dry up the soil and turn it flammable. Prevailing dry conditions affect the flammability of dead forest fuel, whose moisture content is already low compared to live fuel (Tanskanen and Venalainen, 2008; and references therein)

Objectives

Results

Conclusion