0730-B3

Prevention and Control of Wildfires in the Vicinity of Inhabited Localities

Volokitina A.V. ¹, Sofronov M.A. ¹, Matveev P.M. ², Sofronova T.M. ²

Abstract

The following was established on the basis of analysis of such emergency situations in Russia:

1) emergency situations are usually caused not by fires occurring near an inhabited locality but by a large wildfire approaching an inhabited locality;
2) emergency situations can be caused by crown as well as by intensive surface fires;
3) change of wind direction approximately by 90° contributes to quick increase of fire area, when a long fire flank becomes a large fire front;
4) under a very strong wind, a crown fire can approach an inhabited locality at the speed of 6 km/h; such winds are typical of deep valleys, mountain ones, in particular;
5) burning particles thrown before a fire front at a distance of up to 500-600 m cause numerous ignitions in inhabited localities.

Investigation of large post-fire areas showed that surface fire intensity, which contributes to transfer of a surface fire into crowns of conifers, increases considerably, as a rule, not in places of vegetation fuels (VF) accumulation but in places where a strong wind can penetrate into a forest and spread under its canopy.

In the recommendations, two methods of protection are considered: 1) active, and 2) passive. An active method of antifire arrangement aims at creation of conditions to stop effectively an approaching large wildfire by backfiring from a supporting line prepared in advance (at a distance of over 500 m from an inhabited locality). A passive method implies creation of a territory (zone) 600 m wide around an inhabited locality, which cannot burn, by means of regular preventive prescribed burning. Protective measures are elaborated and put into practice on the basis of large-scale VF maps application.

Theoretical fundamentals are elaborated for protection of inhabited localities from emergency situations connected with wildfires (forest and other fires).

Introduction

According to predictions, rise of average global temperature by 1_-2_ is expected by the middle of the 21^st century. This can lead to considerable changes in climate and reformation of the whole biota. Therefore, the UN Convention on Climate Change was accepted in June 1992. This Convention was ratified by Russian Federation in October 1994 and came into force. On the basis of this Convention, the Special Federal Program: "Prevention of dangerous climate changes and their negative consequences for the period till 2000" was created and was accepted by the Russian Federal Government in June 1996. Thus, global and regional changes of environment and climate are not considered to be the subject of pure theory.

It has been proved that climatic changes occur with extreme declination of seasonal weather variations and may cause large-scale fire emergency situations (Stocks, 1993; Wein & Groot, 1996; Fosberg et al. 1996). In recent years, climate changes are vividly seen in the southern part of Siberia and the Far East. They are the cause of intensified spring and summer droughts. Due to these droughts, such emergency situations often occur when forest and steppe fires become dangerous for inhabited localities and even inflict casualties.

In this paper the following questions are considered:

1) determination of inhabited localities and structures that can be damaged by vegetation fires (forest fires, steppe fires etc.);
2) elaboration of vegetation fire preventive measures for protection of such structures;
3) forecast of the probable dangerous development of vegetation fires close to inhabited localities or industrial structures;
4) quick and safe fire stops with the least expense of means.

Some Information on Emergency Situations caused by wildfires in Russia

Severe droughts contribute to increase of forest fire occurrence and fire emergency situations (FES). The incidents when forest and steppe fires become dangerous for inhabited localities and industrial structures or inflict casualties are of great significance.

In Russia, information on catastrophic forest fires and FES involved was kept secret from the 30s till the 90s. Therefore, we know only about forest fires of 1921 in the Mari Al Republic, which destroyed 60 inhabited localities.

After censorship abolition, information on FES in the Russian Federation have been published almost yearly. The year of 1996 is noted particularly.

Irkutskaya oblast. In the Nizhneudinsk raion, 23 buildings were destroyed by fire on May 7, 1996. In other raions - 117 houses and industrial buildings on May 13, 1996. In the Tulunsk raion - 6 houses on May 18, 1996.

Buryatiya. In the Tunkinsk raion, the settlement Ulbugay (26 houses) was burnt down and the majority of houses in the Solnetchnoe settlement were destroyed by crown fire occurred in pine stands on May 7, 1996.

Mari Al Republic. On May 16, 1996, the Koshevo village (26 houses) was burnt down by forest fire.

In 1997, in the Chita oblast, one half of a large settlement was burnt down by steppe fire; inhabited localities and agricultural enterprises in the Khakasiya Republic were damaged to a great extent.

Sakhalin Island. In 1998, five settlements as well as the Gorky settlement (89 houses) were burnt down.

Irkutskaya oblast. In May 2002, a settlement was burnt down by forest fire.

In foreign countries, emergency situations caused by wildfires occur rather often as well.

We have investigated some large forest fires which destroyed the villages in the Boguchansky region of the Krasnoyarsky Krai and in the Buryatiya Republic. It was established:

1. Inhabited localities may ignite from both crown and intensive surface fires. Wildfire, which is large enough (over 100ha) and occurs close to an inhabited locality, may be dangerous for this locality if the wind turns in the direction of the inhabited locality. Thus, it is advisable to be ready to protect an inhabited locality by means of backfiring or to carry out backfiring well in advance. In case when the wind changes its direction, a long flank of wildfire may turn into a wide front.

2. In deep valleys, mountain ones in particular, strong winds are highly probable and can considerably reinforce forest fires by turning them into crown ones in coniferous stands. Crown fires under a strong wind can spread at a high rate - 3-7 km/hour. A great number of burning particles is thrown before the fire front at a distance of not less than one half of a kilometre. Approach of such a fire to the inhabited locality may be absolutely unexpected for the inhabitants. As a result, it is practically impossible to arrange an active protection by means of backfiring done in advance. Under similar conditions, only a wide stripe (not less than 0.6-0.7 km wide), which prevents intensive fire spread, can protect an inhabited locality.

3. Wildfire area can rapidly increase under influence of wind direction changes and become dangerous for inhabited localities nearby.

Conditions of emergency situations development caused by wildfires

From the analysis of the information on damage and destruction of inhabited localities by wildfires (forest, steppe, bush), we can conclude the following:

1. Inhabited localities are damaged and destroyed by large wildfires, which occur and develop in the distance from inhabited localities and then approach as a wide fire front. Fires, which occur close to inhabited localities, are quickly suppressed, as a rule, in the initial phase. Therefore the main task is not to extinguish and suppress the whole fire approaching an inhabited locality but to protect an inhabited locality from it.

2. Inhabited localities can be damaged and destroyed by crown fires as well as by intensive surface fires (forest and steppe).

3. Development of large intensive wildfires is predetermined by phenological state of vegetation and weather conditions (drought level, wind). Often changes of wind directions during fire contribute to it as well, as a result of which a long fire flank becomes a wide fire front.

4. Large intensive wildfires develop, as a rule, under usual load of vegetation fuels (VF), since fire intensity is determined by two factors: by VF load burning in flame regime at the fire edge as well as by rate of fire spread (influenced by wind and slope). Fires reach high intensity more often in the areas, where the wind penetrates under forest canopy and increases considerably fire rate. The reached intensity and rate can remain at the same level at the expense of burning particles, which are thrown before the fire front (i.e. at the expense of "spotted" form of spread), for quantity of burning particles becomes larger as fire intensity increases.

5. Houses in inhabited localities catch fire from burning particles, which are thrown by the wind before the front of a large intensive fire at the distance of 500 m and over.

6. Relief can produce a great impact on wind direction and wind speed. For example, in deep valleys, the wind blows along valleys and becomes stronger in their narrow places.

Technique on determination of inhabited localities and other objects, which can be damaged by forest fires

This is the most complicated and labour-consuming task. At first, it is necessary to establish a complex of conditions (taking into account different variants), under which emergency situations can develop, moreover, theoretical elaborations should be supplemented by thorough study of actual events of similar emergency situations.

The elaborated technique on determination of inhabited localities and other objects, which can be damaged by wildfires, includes the following stages:

a) at first, potential fire hazard and fire occurrence in forests of the region are assessed, especially in terms of large wildfire development;

b) then inhabited localities on the territory where coniferous forests prevail are marked (since crown fires can develop in coniferous forests); for this purpose, maps of forests, maps of forest fund, and medium-scale VF maps can be applied;

c) among the marked inhabited localities, those with distance less than 500 m between the border of a coniferous forest and houses close to it are selected; for this aim, plans of forest stands, topographical maps at 1:25 000 scale and airborne images (or ordinary pictures made from a plane or helicopter) can be applied because the territory with forests plots on it adjacent to the settlement may not be a part of the State Forest Fund (Goslesfond) and may not be found in the plans of forest stands;

d) location of the selected inhabited localities on the relief is analysed in terms of influence of the relief on wind direction and speed; special attention is given to the objects located in the places where the wind can become stronger (e.g. in the narrow places of deep valleys); for this purpose, a topographical map is applied.

Elaboration of Arrangements on Protection of Inhabited Localities from Wildfires

1. Inhabited localities can be destroyed by large wildfires (not only crown but also intensive surface ones) from outside.

Consequently, to protect an inhabited locality, it is not at all obligatory to extinguish the whole fire (that may be extremely difficult); the most important thing is to stop the part of fire edge that approaches an inhabited locality.

2. Inhabited localities catch fire from burning particles, which are thrown by an intensive wildfire before its front at the distance up to 500 m.

Consequently, a fire edge should be stopped at the distance not less than 500 m from an inhabited locality.

3. It is almost impossible to stop an intensive wildfire even by a wide mineralized stripe, since the fire can get over the stripe at the expense of burning particles thrown before the front.

The only efficient method to stop such a fire is to burn a wide stripe of surface cover before its front.

4. It is known that crown fires can jump from crown to crown at a distance up to 200 m (without surface fire support), or even farther, according to pilots-observers. It is also known that fires get over barriers (rivers, swamps) up to 500 m wide by throwing burning particles across them.

Consequently, the burnt protective stripe should be not less than 500 m wide.

Two methods of protection are possible:

1. Active method of protection - quick burning of a protective stripe by means of backfiring in case of approaching large fire. it is obligatory to have a supporting line for backfiring in the mode of a linear barrier earlier prepared at a distance of 500 m around an inhabited locality as a preventive measure. This method is not expensive but its efficiency depends upon a correct choice of time for backfiring in relation to fire behavior forecast, upon correct organization of work during backfiring, and moreover upon available time sufficient for backfiring procedure. The point is that if a fire quickly approaches under influence of a strong wind or if information on dangerous fire situation is not received in time, no time may be left for organization and realization of backfiring.

2. If an inhabited locality is located on the territory where there is a danger of quick crown fires development, a second method is applied, i.e. arrangement of a protective stripe (zone) not less than 500 m around an inhabited locality well in advance and its constant maintenance in a non-flammable state as a preventive measure and as a method of passive protection. It should be noted that area covered with vegetation becomes non-flammable only under regular removal of the prime conductor of burning by prescribed burning (in grass forest types - annual prescribed burning in fall, in moss forest types - in 2-3 years). Such measures are quite difficult for putting into practice and require constant expenses.

The second method of protection is additional in relation to the first method, since at first conditions for active protection of an inhabited locality by backfiring should be prepared, then if necessary, a protective non-flammable zone should be arranged and maintained.

Protective measures are elaborated and put into practice on the basis of a created information database.

Information database should, first of all, include information on territories around an inhabited locality in the mode of specialized maps and plans necessary for planning and realization of measures on protection of an inhabited locality from wildfires. This information includes:

1) pyrological characteristic of vegetation in the mode of a large-scale VF map supplemented with pyrological description of inventory plots on the map;
2) information on accessibility of the territory in the mode of detailed data on a road net;
3) information on pyrological partition of the territory by different barriers (roads, streams, mineralized stripes, etc.), which can be used as supporting lines for active fire fighting.

The main component of information database is a large-scale VF map supplemented with pyrological description of forest inventory plots on the territory 3-5 m around an inhabited locality.

VF maps are necessary for: 1) optimal choice of a route for creation of a supporting line (stripe) used in backfiring to protect an inhabited locality from an approaching large fire; 2) behavior forecasting of an approaching large fire (to be more exact, of the part of its edge, which can be dangerous for an inhabited locality); 3) behavior forecasting of a backfiring edge; 4) determination of ignition places (if ignitions occur from burning particles on the territory close to an inhabited locality), assessment of fire hazard of each ignition, planning of prompt delivery of forest fire fighters to them and effective extinguishing.

Technology of large-scale VF maps creation is elaborated (Volokitina, Klimushin, Sofronov, 1995). Plan of forest stands (to be more exact, black-and-white map-cases) and forest inventory description serve as a base of a large-scale VF map. The created VF map is supplemented by a pyrological description of forest inventor plots. At present, in forest enterprises, records of forest inventory data are often not accessible. In such cases, we use not an automated but "handy" method of VF map creation. It is quite possible since the map is required for a comparatively small area around an inhabited locality. Besides, usually not the whole territory close to an inhabited locality is included in the State Forest Fund and can be found in the plan.

The whole road net as well as streams and rivers are marked on the VF map. If a territory has an expressed relief, it is better to copy contour lines from a topographical map into a VF map.

Forest inventory information can be not sufficiently complete and accurate, and even out of date. Therefore, the information should be corrected and supplemented by means of route investigations around a settlement as well as by examination and making pictures of this territory from a plane.

Preparation for an active protection of an inhabited locality. For this purpose, it is necessary at first to mark on the plan and in the locality and then to create a supporting line (stripe) for backfiring. A supporting stripe should surround a settlement from all sides or its ends should join non-flammable areas (a broad river, a plough field, etc.). A supporting stripe should be made at a distance of not less than 600 m from a settlement and should be continuous.

A route of a supporting stripe is arranged so that it could include parts of existing roads and paths, if possible. Non-burnable plots (swamped, streams, wet valleys of streams), plots difficult to burn (Politrichum and damp moss forest types), plots difficult to traverse (debris, dense young trees) should not hamper backfiring, i.e. they should be not before a stripe, but behind it. In broken terrain, a route of a stripe should go along watersheds and along (not across) slopes. Before a stripe, their should be no steep slope, on which backfiring may turn into an intensive fire. An external side of a supporting line (stripe) should be cleared from windfallen trees, branches and from young growth at a distance up to 50 m.

On the basis of a VF map, it is useful to make in advance maps of current potential fire danger (readiness of forest inventory plots to burn) for different seasons (spring, summer) for each class of drought to forecast fire behavior.

As an example, a project of preliminary measures for active protection of the Osinovy Mys (Krasnoyarsky Krai) settlement is created. A supporting stripe surrounds the settlement from three sides, its ends join the Chuna river. From western and eastern sides, the route goes, mainly, along forest roads, which run up valley slopes, and from northern side - along an upper part of a slope on clearance.

Conclusion

Theoretical fundamentals are elaborated for protection of inhabited localities from emergency situations connected with wildfires (forest and other fires).

The following was established on the basis of analysis of such emergency situations in the Krasnoyarsky and Altaysky krai and in Buryatiya Republic:

1) emergency situations are usually caused not by fires occurring near an inhabited locality but by a large wildfire approaching an inhabited locality;

2) emergency situations can be caused by crown as well as by intensive surface fires;

3) change of wind direction approximately by 90˚ contributes to quick increase of fire area, when a long fire flank becomes a large fire front;

4) under a very strong wind, a crown fire can approach an inhabited locality at the speed of 6 km/h; such winds are typical of deep valleys, mountain ones, in particular;

5) burning particles thrown before a fire front at a distance of up to 500-600 m cause numerous ignitions in inhabited localities.

Investigation of large post-fire areas in the Priangarie showed that surface fire intensity, which contributes to transfer of a surface fire into crowns of conifers, increases considerably, as a rule, not in places of VF accumulation but in places where a strong wind can penetrate into a forest and spread under its canopy.

As a result, practical recommendations are elaborated on "Protection of inhabited localities from emergency situations connected with wildfires".

In the recommendations, two methods of protection are considered: 1) active, and 2) passive. An active method of antifire arrangement aims at creation of conditions to stop effectively an approaching large wildfire by backfiring from a supporting line prepared in advance ( at a distance of over 500 m from an inhabited locality. A passive method implies creation of a territory (zone) around an inhabited locality, which cannot burn, by means of regular preventive prescribed burning. An active method can be supplemented with a passive method if an inhabited locality is situated on the territory having danger of development of quick crown fires.

Protective measures are elaborated and put into practice on the basis of large-scale VF maps application. In the Appendices for Recommendations, a technology of VF maps creation on the basis of forest inventory information is given and sequence of fire behavior forecasting by making use of VF maps and meteorological information is suggested.

REFERENCES

Fosberg M.A., Stocks B.J., Lynham T.J., 1996. Risk analysis in Strategic planning: Fir and climate change in the boreal forest // Fire in ecosystems of boreal Eurasia, Kluwer Acad. Publ., eds. Goldammer J.G., Furyaev V.V, pp.495-504.

Stocks B.J., 1993. Global warming and forest fires in Canada. For. Chron. 69, p.290-293.

Volokitina A.V., Klimushin B.L., Sofronov M.A., 1995. Technology of large-scale vegetation fuel maps creation. practical recommendations. Krasnoyarsk, Institute of Forest SB RAS, 47 p. (In Russian)

Wein R.W., Groot W.J., 1996. Fire-climate change hypotheses for the taiga // Fire in Ecosystems of Boreal Eurasia. Kluwer Acad. Publ., eds. Goldammer J.G., Furyaev V.V., pp. 505-524.

¹ V.N. Sukachev Institute of Forests, Russian Academy of Sciences.Akademgorodok, Krasnoyarsk, 660036; Russia;Fax: (7)-(3912)-43-36-86;
E-mail: [email protected];
² Siberian State University of Technology, Prospekt Mira, 82, Krasnoyarsk, 660049, Russia; Fax: (7)-( 3912)-66-03-90;
E-mail: [email protected]