Seasonality of Forest Fires in Bhutan

(IFFN No. 10 - January 1994, p. 5-9)

Background

Bhutan is a mountainous country which lies between 26° 45' and 28° 30'N and 88° 45' and 92° 10'E. The total geographical area of the country is 46,500 km² out of which 26,338 km² (i.e. 56.6%) area is covered by forest. Further break-down of vegetation types and coverage by these types are given in Table 1. The climatic variations from region to region are considerable; summers being hot and humid with temperatures soaring to 30 to 35° C in the South, but cool and pleasing in the Western, Central and Eastern regions of the country with average temperatures of 19 to 22° C. The freezing dry winters in Western and some parts of the Central and Eastern territory contrast with mild pleasant temperatures in the South. The changes in climate occur within a short distance. Therefore we can say that there is a great diversity of climate, possibly greater than any other area of similar size in the world.

The forests are the most important natural wealth of the country. The future economy of the people and the country is very much dependent on its protection, conservation and scientific management." (The Bhutan Forest Act, 1969)

 

Tab.1. Distribution of forest vegetation types in Bhutan by percentage of land cover.

Tab.2. Causes of fire starts in Bhutan.

The south-west monsoon starting in June and lasting for four months, accounts for 86 to 97% of annual precipitation. Precipitation varies with the valleys' exposure to the rain bearing monsoon winds. Parts of the valleys located in the rain shadow are dry. On the higher mountains the little precipitation during winter comes mainly in the form of snow, beginning at the end of November. Occasionally snow reaches down to 2250m amsl but it does not last more than two days. Whereas at the altitudes of 2500 to 3000m amsl it remains on the ground only in sheltered places. Beyond 3000m amsl it can last much longer from mid-December to early March especially under shelter and on North facing slopes.

Forest Fire Situation
Forest fire is one of the biggest threats to our forest resources. Blue pine, chir pine, mixed conifer, broadleaf with conifer, plantations and degraded forests, which cover approximately 40% of the total forest area, are most susceptible to frequent forest fires. Repeated forest fire, combined with heavy grazing pressure, can completely degrade vegetation cover. Proper attention should be given to prevent forest fires causing further degradation of remaining forests. Once the forest is degraded, it is difficult to restock it in the original shape by means of reforestation.

In Bhutan, forest fire incidence is normally high during the dry winter months. Freezing temperatures and lack of rainfall are responsible for drying of perennial grasses, and increasing wind velocity quickens the drying process thereby making the grass covered area inflammable. In the freezing winter, it becomes difficult to live without warming fire. Further land preparation for agricultural, horticultural and shifting cultivation purposes is done during or at the end of the winter months. Fire is used as the cheapest tool for cleaning such land by the villagers and shifting cultivators. As a result, uncontrolled use of fire in or adjacent to the forest occurs frequently. Often such fires escape to the forest accidentally. In some cases, fires are set wilfully by the cattle grazers to obtain new flush of good grasses. So far there is no report on forest fire incidence caused by lightning. Our analysis reveals that in our country 100% forest fire incidence are human-caused, wilfully or accidentally (Tab.2).

Every year 20 to 75 (average 50) forest fires are reported in our country. Most forest fires are caused by escaped fires from agricultural land and orchards. The number of escaped fires can be reduced by adapting appropriate controlled burning techniques in agricultural land and orchards. Uncontrolled use of fire as a tool to improve pasture land should not be considered in any part of the country. If it is a necessity for the survival of livestock, appropriate techniques for burning of pasture land should be developed so as to insure the protection of surrounding vegetation. Similarly, the number of fires escaping from camp fires, cooking fires etc. can be reduced by adopting more restrictions through rules and regulations. Appropriate prevention modules for different types of target groups, such as agriculturists, orchard owners, herders etc. should be designed. Various target groups should be made aware of the value of the forests. Only then would we be going in the right direction towards achieving good-will of the people. Prevention is better than cure. Therefore every effort should be made to prevent forest fires. If there is honour with our people in preventing forest fires, then the fire incidence could be avoided.

Some years like 1979, 1981, 1982, 1983 and 1989 were comparatively dry years and in most parts of the country pre-monsoon rains were delayed and very much limited. As a result the number of fire cases increased.

On the other hand, nowadays more land is brought under utilization for various purposes. As such there is every likelihood of increasing the numbers of escaped fires. Therefore, it is time to consider prevention approaches through various media and the enrolment of villagers in forestry programmes (social, community and agroforestry) which play a vital role in educating people on the importance of forests and developing good will to minimize destruction of the forest.

Rainfall Distribution Pattern and Fire Risk Zones

Most parts of our country in the Western and Eastern region receive no rain or very little (only up to 10 mm) during the months from November to April. In some parts of this region total rainfall for seven months (October to April) is only 150 mm. Based on the local rainfall regimes the country has been divided into three zones of fire risk (Tab.3).

High Fire Risk Zone
The areas with less than 1000 mm annual rainfall can be considered the high fire risk zone. Kurijampa, Tashigang, Tangmachu, Rongtung in the East and Thimphu, Paro, Haa and Wangdi in the West and some rain shadow areas of the Central region fall in this zone. Because of little rainfall, high day-time temperatures and afternoon winds, the forest floor dries out very quickly, leading to a high risk of fire. Chir pine growing areas are also included in this zone because these are occurring mostly in drier sites. If precipitation is more than 1000 mm, it is lost very soon by run-off and evaporation due to lack of sufficient ground cover like undergrowth, humus etc.

 

Tab.3. Zones of wildfire risk in Bhutan.

  p = Total annual precipitation

 

Medium Fire Risk Zone
The areas which receive rainfall of between 1000 mm to 2000 mm per year fall in this zone: Punakha, Hurchi, Langthal, Tongsa, Lame Gompa, Dungkhar, Thrimshing, Khengkhar, Daga Dzong, Dubani, Mangdechu, Dagapela, Shemgang, Chhuka, Tashithang, Yabilabsa and Damphu. The floor of the broadleaved forest in this zone is slightly moist, and as such forest fires are not frequent. However, the zone of chir pine forest remains quite dry, and therefore fires may occur frequently.

Low Fire Risk Zone
Areas with more than 2000 mm annual rainfall are considered as low fire risk zone. All Southern parts of the country like Sarbhang, Samchi, Phuntsholing, Sibsoo, Decheling, Daifam, Samdrupjonkhar, Surey, Deothang, Dungmain and Dorokha fall in this zone. The floor of the evergreen forest is covered throughout the year by green grasses but the floor of deciduous forests is covered with dry fallen leaves and is prone to catch fire during long drought periods.

 

Fig.1. Monthly distribution of forest fire incidents (%) throughout the year in Bhutan

Concluding Remarks

In order to know the overall forest fire situation in the country 393 cases of forest fire were investigated, and the result is shown in Figure 1. It shows that forest fire incidences in the country were observed between October and July, but the risk of forest fire incidences during October - November and June - July is less than 5 %. As such this period cannot be considered as part of the forest fire season.

The period from December to May has more than 5 % the risk of fire incidences. Therefore, countrywide the forest fire season con be considered to be from the first week of December till the end of May, or six month's duration. During February and March the risk of forest fire incidences is more than 15 % and this is considered as the peak forest fire season.

Temperature, pressure, wind speed, wind direction, humidity, visibility, clouds and precipitation are important weather factors. These are always changing, as such weather also changes. It is therefore important to understand and interpret weather variations. These weather factors directly affect the behaviour of a fire. Strong wind and very low relative humidity are two main causes of escaping and accidental fires. The incidence of forest fires is caused mainly by escaped and accidental fires in our country.

Past weather and fire incidence data are manipulated to forecast rainfall and forest fire danger regionally. If weather conditions are indicating some danger, we can regulate the unfavourable forest conditions through management i.e. controlled burning, establishment or cleaning of a fire line, patrolling etc. or by creating awareness among people to prevent damage from fire. The forest fire season and the peak fire season of the Eastern, Western, Central and Southern regions are now known and utmost care to prevent fire during the fire season is expected.

Bhutan Fire Statistics

The following statistics cover the years 1981-85 and were made available to the editor of International Forest Fire News in 1986.

 

Tab.1. Forest fire statistics of Bhutan for the period 1981-1985 (Source: Royal Government of Bhutan)

 

 

From:	D.B. Chhetri
Address:	Ministry of Agriculture, Department of Forestry Royal Government of Bhutan Forest Protection Cell, Forest Research Division P.O.Box 673 Taba-Thimphu BHUTAN

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