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METEOROLOGICAL ASPECTS OF FOREST FIRE DANGER RATING
Abstract
The effect of past weather conditions on inflammability and the influence of weather on fire behaviour are discussed. Using a method of deriving inflammability from rainfall, temperature and humidity data the frequency of days of high inflammability in January, February and March in the Cape over eight years is derived and shows a maximum in mid-February. With the use of a burning index meter daily values of fire danger rating at the Cape for the same months in 1953–1955 are derived. Attention is called to the advantages of an objective method of forest fire danger rating and the role meteorological forecasts can play in fire protection.
... Unfortunately wind is the factor most difficult to forecast accurately and it causes most problems in prescribed burning (Green, 1981). This is especially true for the fynbos biome, where local winds often enhance the channelling of synoptic scale winds, so that zones of localised strong winds occur (King, 1957;Fuggle, 1981). Fuggle (1981) concluded that it is impossible to generalise about wind patterns in the fynbos biome as local conditions are so highly variable. ...
... Mean wind speed at a mountain station can be up to twice as great as that in a valley bottom (see Jakkalsrivier in Figure 3). Second, diurnal fluctuations in wind speed are usually considerable (King, 1957) and this makes the mean daily wind speed an unsuitable parameter. However, the definition of suitable wind speeds for safe burning is not a difficult task. ...
The fynbos vegetation of the Cape mountains is managed by applying what is termed prescribed burning. Burns are carried out under conditions of weather and fuel that are selected to ensure a safe and efficient burn. Formal prescriptions for burning in fynbos do not exist, but air temperature and days since last rain are the most important factors currently used to select days for burning. The conditions currently favoured by managers for burning were used to define preliminary prescriptions. Strict selection for time since last rainfall currently limits the number of suitable days available but could become less important if strict attention is given to other factors. Suitable conditions of wind, temperature and humidity will also limit the number of days suitable for burning. The seasonal occurrence of prescribed conditions was examined at seven weather stations in four zones of fire climate in the fynbos biome. Burning should take place in March and April in the inland zones, but may be undertaken from November to April in the south-western coastal zone. Fires in the humid south-eastern coastal zone should take place only when the desired fire intensity can be achieved. This may be in winter or summer, but more research is needed to determine the optimum season in this zone. Suitable burning days are rare in the recommended seasons and suggestions for the efficient use of available burning days are made.
... Dew Point Temperature Nesterov, 1949Mazzeo et al., 2022Relative Humidity McArthur, 1967Van Wagner, 1974;Deeming et al., 1977;Andrews, 1986Zhang et al., 2010Sirca et al., 2018;Cavalcante et al., 2021Precipitation McArthur, 1967Van Wagner, 1974;Deeming et al., 1977;Andrews, 1986Zhang et al., 2010Caccamo et al., 2012;Sirca et al., 2018;Cavalcante et al., 2021Wind Speed McArthur, 1967Van Wagner, 1974;Deeming et al., 1977;Andrews, 1986Zhang et al., 2010Cavalcante et al., 2021 Wind Direction Andrews, 1986;Finney, 1998;Parisien et al., 2005;Finney, 2006;Yang et al., 2008Tymstra et al., 2010 Cloudiness Deeming et al., 1977-Vapor Pressure Deficit Landsberg, 1986Nolan et al., 2016Lightning Frequency Deeming al., 1977Kourtz and Todd, 1992;Hessburg et al., 2007Chuvieco et al., 2012Liu et al., 2012;Krause et al., 2012 Net Solar Radiation King, 1957Vilar et al., 2011 Julio, 1990;Cardille et al., 2001;Vilar del Hoyo et al., 2008;Martinez et al., 2009Ponomarev et al., 2015Costafreda-Aumedes et al., 2018;Rodriguez et al., 2018 Population ...
Wildfires have been systematically studied from the early 1950s, with significant progress in the applied computational methodologies during the 21st century. However, modern methods are barely adopted by administrative authorities, globally, especially those considering probabilistic models concerning human-caused fires. An exhaustive review on wildfire danger studies has not yet been performed. Therefore, the present review aims at collecting and analyzing integrated modeling approaches in estimating forest fire danger, examining the driving factors, and evaluating their influence on fire occurrence. The main objective is to propose the top performing methods and the most important risk factors for the development of an Integrated Wildfire Danger Risk System (IWDRS). Studies were classified based on the applied technique, i.e., geographic information systems, remote sensing, statistics, machine learning, simulation modeling and miscellaneous techniques. The conclusions of each study concerning the relative importance of model input variables are also reported. Online search engines such as 'Scopus', 'Google Scholar', 'WorldWideScience', 'ScienceDirect' and 'ResearchGate' were used in relevant literature searches published in scientific journals, manuals and technical documentation. A total of 230 studies were gathered with a selected subset being evaluated in a meta-analysis process. Machine learning techniques outperform average classic statistics, although their predictability relies heavily on the quantity and the quality of the input data. Geographic information systems and remote sensing are considered valuable yet supplementary tools. Modeling techniques apply best to fire behavior prediction, while other techniques referenced in the current review are potentially useful but further investigation is needed. In conclusion, wildfire danger is a function of seven thematic groups of variables: meteorology, vegetation, topography, hydrology, socio-economy, land use and climate. Ninety-five explanatory drivers are proposed.
... The hazard by wildfires may be represented in a quantitative way by defining a rating index, frequently called fire danger, to better support the integrated analysis of the factors determining the ease of ignition, rate of spread, difficulty of control and fire impact [14,18]. The literature on how to implement effective fire danger rating systems encompasses several decades of research [12,63,15,90,37]. Among these long-lasting research programs, the Canadian one began in 1925 and led to the development of several fire danger systems [106] with successive improvements to account for the effects of weather on forest fuel and fire [18]. ...
This research focuses on European wildfire danger and vulnerability under a changing climate, to support the integration of some main climate-related components of wildfire risk. A detailed assessment is proposed on the varying frequency of fire danger classes (from the relatively safer to the extreme danger conditions) under changing climate. On a given area, the co-occurrence of an increasing number of high-danger days, and the presence of people potentially exposed to wildfires, and living within the more vulnerable interface between settlements and wildland, indicates an increasing fire risk. Focusing on the population potentially exposed to wildfires in Europe, the interface between urban areas and wildland (WUI) is here identified as an indicator of where the people are more vulnerable, both due to the easier ignition of areas where people can have an easier access to wildland, and due to a passive consequence of the increased risk. Once a given fire is ignited close to the WUI, neighbour locations are also threatened. In addition, summary indices of potential vegetation vulnerability are introduced to account not only for single species vulnerability, but rather for the combined multifaceted impacts on vegetation structure and composition following the definition of ecological domains by FAO and estimating their potential shift under different climate-change scenarios. An integrated assessment of the findings supports a recommendation to focus on the Mediterranean areas of Europe characterised by higher potential vegetation and population vulnerability, and higher potential fire danger. In addition, attention may be necessary to specific mountain areas (even outside the Mediterranean) especially on lower elevation areas where forests are dominant and more vulnerable to a rapidly changing ecology, and land abandonment may worsen the vegetation fuel and the WUI interface for the remaining population.
... ↑ ≡ 2 Weather, climate and fire danger: the Canadian Forest Fire Weather Index system Fire danger may be quantitatively defined as a rating index to support the assessment of the factors which determine the ease of ignition, rate of spread, difficulty of control and fire impact [53,16]. The study of fire danger rating systems and their relationship with weather patterns has been active for several decades and is strategic in the many countries where forest resources, their management and sustainability play a vital role [54,55,56,57,58]. ...
Forests cover over a third of the total land area of Europe. In recent years, large forest fires have repeatedly affected Europe, in particular the Mediterranean countries. Fire danger is influenced by weather in the short term, and by climate when considering longer time intervals. In this work, the emphasis is on the direct influence on fire danger of weather and climate. For climate analysis at the continental scale, a daily high-emission scenario (RCP 8.5) was considered up to the end of the century, and a mitigation scenario that limits global warming to 2 °C was also assessed. To estimate fire danger, the Canadian Fire Weather Index (FWI) system was used. FWI provides a uniform numerical rating of relative fire potential, by combining the information from daily local temperature, wind speed, relative humidity, and precipitation values. The FWI is standardised to consider a reference fuel behaviour irrespective of other factors. It is thus well suited to support harmonised comparisons, to highlight the role of the varying climate in the component of fire danger that is driven by weather. RESULTS. Around the Mediterranean region, climate change will reduce fuel moisture levels from present values, increasing the weather-driven danger of forest fires. Furthermore, areas exhibiting low moisture will extend further northwards from the Mediterranean, and the current area of high fuel moisture surrounding the Alps will decrease in size. Projected declines in moisture for Mediterranean countries are smaller with mitigation that limits global warming to 2 °C, but a worsening is still predicted compared with present. There is a clear north-south pattern of deep fuel moisture variability across Europe in both climate change scenarios. Areas at moderate danger from forest fires are pushed north to central Europe by climate change. Relatively little change is expected in weather-driven fire danger across northern Europe. However, mountain systems show a fast pace of change. ADAPTATION OPTIONS. Key strategies to be considered may include vegetation management to reduce the likelihood of severe fires, as well as fuel treatments to mitigate fire hazard in dry forests. These measures should be adapted to the different forest ecosystems and conditions. Limited, preliminary knowledge covers specific but essential aspects. Evidence suggests that some areas protected for biodiversity conservation may be affected less by forest fires than unprotected areas, despite containing more combustible material. Specific typologies of old-growth forests may be associated with lower fire severity than densely stocked even-aged young stands, and some tree plantations might be more subject to severe fire compared with multi-aged forests. Particular ecosystems and vegetation associations may be better adapted for post-fire recovery, as long as the interval between fires is not too short. Therefore, deepening the understanding of resistance, resilience and habitat suitability of mixtures of forest tree species is recommended. Human activity (accidental, negligent or deliberate) is one of the most common causes of fire. For this reason, the main causes of fire should be minimized, which includes analysing the social and economic factors that lead people to start fires, increasing awareness of the danger, encouraging good behaviour and sanctioning offenders. LIMITATIONS. Bias correction of climate projections is known to be a potential noticeable source of uncertainty in the predicted bioclimatic anomalies to which vegetation is sensitive. In particular, the analysis of fire danger under climate change scenarios may be critically affected by climatic modelling uncertainty. This work did not explicitly model adaptation scenarios for forest fire danger because ecosystem resilience to fire is uneven and its assessment relies on factors that are difficult to model numerically. Furthermore, a component of the proposed climate-based characterization of future wildfire potential impacts may be linked to the current distribution of population, land cover and use in Europe. The future distribution of these factors is likely to be different from now.
With the aid of experiments and the known properties of timber and combustion, an objective fire-danger rating system is developed, where each contributing factor can be expressed by a numerical value.
Hygrothermographic fire danger rating and forecasting
- D A N Cromer