Why Does Smog Occur Every Year in the Northern Region of Thailand?

The northern region of Thailand used to be a sought-after destination for both local and international tourists, with its beautiful scenery and pleasant weather. However, the people in the area have been facing the problem of smog and haze for many years, and it never really subsides.

Every year from March, the clear blue sky has turned hazy and filled with smoke, and the once-clean air is now filled with dust.

Over 80% of the cause of the smog in the northern region comes from burning including forest burning and farm burning, and sometimes it spreads from neighbor countries such as Laos and Myanmar.

Recently the member of the Northern Respiratory Alliance and the Anandamahidol Foundation have conducted a search and found that there are areas of repeated burning in the same spots in the northern region since 2010-2017, totaling over 1 million rai (350,000 acres).

When forest fires occur, the air does not circulate, causing smoke and dust to be trapped all over the region. Moreover, the weather conditions in northern region do not change frequently, the smoke and dust will increase even more.

Why do forest fires occur every year?

Image: Nion Sirimongkonlertkul (The outcomes of new application for controlling smoke haze problem in Chiang Rai)

Forest fires and haze are problems that people in the Northern region have to face every year. It usually occurs between the end of February and the beginning of May, it’s known as “Burning Season”

Forest fires may occur naturally or as a result of human activities, and a single spark can spread to hundreds of acres within a few days.

For the natural causes, geography of the Northern region is the main factor why forest fires occur every year. The region mostly consists of high mountains and plateaus. The characteristics of the forest here are different from other parts of the country. During the hot season, dry leaves and branches become fuel.

In addition to natural factors, human activities such as slash-and-burn agriculture and forest harvesting are also causes of forest fires. Many people who live in high areas in the northern region practice slash-and-burn farming for a long time.

They burn forests to start a new farming cycle or to help certain crops grow, such as sweet potatoes or mushrooms, when trees and grass cover the ground too much, making it difficult to grow crops. Therefore, villagers believe that burning forests makes it easier for them to collect forest products.

According to statistics collected from forest fires from 1985 to 1999, there were a total of 73,630 forest fires, and only 4 of them were found caused by natural causes such as lightning.

Forest fires in northern Thailand caused by humans can be classified into 3 main types


The majority of villagers in the northern region engage in subsistence agriculture. Most of the burning is caused by those villagers. For example the burning of corn stalks used for animal feed. There are also burnings of sugarcane for harvesting and burnings of rice straw in the flatlands to prepare for the next planting season.

Burning is seen as the most cost-effective method because of its low cost, short time requirement, and ease of use.

In addition, there are burnings in accordance with the traditional way of life of the villagers in the highland areas, believing that the burnt soil will increase the production of forest plants such as grass, animal feed, sweet vegetables, and mushrooms.

1. Forest scavenging
The act of forest scavenging is the main cause of forest fires. The collection of forest products, mostly through fire, is done to clear the forest floor for easier navigation or to provide light during nighttime travels through the forest. Fires may also be set to stimulate the growth of mushrooms or to promote new leaf growth, or to drive away red ants or smoke bees and other insects while in the forest

2. Field brining
Burning fields is a significant cause that follows the previous mentioned causes. Burning fields is done to eliminate weeds or plant residues after harvesting. This is done to prepare the area for the next crop without any control or firebreaks. The fire can then spread to nearby forests.

3. Intentional burning or arson
Both in terms of sabotage and in cases where local residents have conflicts with government agencies in the area, particularly regarding issues of land use or illegal logging activities in the forest.

How much forest have been lost?

The statistics from the Chiang Mai University Respiratory System Research Unit, indicate the total area of forests in the northern region of Thailand, the number of hotspots found, and the extent of forest fires in the region as follows.

The forest area in 9 provinces of the northern region in 2019 is approximately 45 million rai. There were 63,000 hotspots detected, and the total area burned was approximately 5.5 million rai (12.2% of the total forest area). It can be divided into the following.

  1. Deciduous forest with an area of approximately 11 million rai (25% of the total forest area). There were 15,000 hotspots detected, and the area burned was approximately 1.3 million rai (2.9% of the total forest area).
  2. Mixed forest with an area of approximately 19 million rai (42% of the total forest area). There were 31,000 hotspots detected, and the area burned was approximately 2.7 million rai (6% of the total forest area).
  3. Evergreen forest with an area of approximately 15 million rai (33% of the total forest area). There were 17,000 hotspots detected, and the area burned was approximately 1.5 million rai (3.3% of the total forest area).

What about its impacts?

The problem of air pollution from smog and particulate matter that occurs during the period from February to March has had a significant impact on the landscape of tourist destinations such as Chiang Rai and Chiang Mai in the past 4-5 years. It has caused a loss of more than 2 billion baht to the tourism industry in Chiang Mai alone. While the number is not available for Chiang Rai but the amount loss in tourism is definitely high. Smoke also led to an increase in respiratory illnesses such as asthma and lung cancer.

According to research by Dr. Pongstaporn Wiroonpanichadet, Faculty of Medicine, CMU, it was found that Chiang Mai province has a lung cancer patient rate of approximately 40 people per 100,000 population, while other regions have an average rate of approximately 20 people per 100,000 population. Therefore, people in Chiang Mai have a chance of contracting lung cancer up to 2 times higher than people in other regions.

Dr. Pongstaporn suggests that if the problem of air pollution in the northern region has not been effectively addressed, there is concern that in the next 10 years, there will be a significant increase in lung cancer patients especially in Chiang Mai and Chiang Rai.

Source: BOT Magazin

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