Every year, from late January through April, Northern Thailand, and especially Chiang Mai, is engulfed in what is commonly referred to as the "smokey season." This phenomenon is characterized by thick, smoky air hanging over the region, reducing visibility and elevating health risks for locals and visitors alike. The "smokey season" is the direct result of a combination of factors, but the most significant contributor is the widespread use of "slash-and-burn" agriculture.

What Is smokey season?

Smokey season refers to the months when air quality in Chiang Mai and surrounding areas deteriorates drastically due to smoke from burning agricultural fields. Farmers in Northern Thailand, as well as in neighboring countries such as Laos and Myanmar, continue to rely on slash-and-burn farming to clear their land for the next planting season. This involves burning off the remnants of crops and vegetation to fertilize the soil, but the process releases vast amounts of smoke and particulate matter into the atmosphere.

Chiang Mai is especially vulnerable to the effects of smokey season due to its geographic location. The city sits in a valley surrounded by mountains, which trap the smoke and pollution, preventing it from dispersing easily. The result is a "smoke blanket" that hangs over the city, and its intensity can vary depending on wind patterns and rainfall, but it typically peaks between February and March.

Why do farmers still use slash-and-burn?

The use of slash-and-burn agriculture persists for several reasons, despite its detrimental environmental and health effects. First and foremost, it is a low-cost method for clearing land and enriching the soil. Many farmers in Northern Thailand and neighboring countries rely on this technique because it is inexpensive, quick, and effective. For small-scale farmers, alternative methods like mechanized farming or other sustainable practices may not be financially viable, especially in rural and impoverished areas. Additionally, some farmers believe that burning leftover crops like corn and sugarcane helps boost productivity by fertilizing the soil with ash.

Moreover, tradition plays a role. Slash-and-burn farming has been practiced for centuries in Southeast Asia, and while awareness of its environmental impact is growing, changing longstanding cultural practices is a slow and complex process. Government efforts to curb the practice are often met with resistance, as many farmers see it as an essential part of their livelihood.

When does smokey season occur?

The timing of smokey season varies slightly each year, depending on weather conditions and agricultural cycles. It generally begins in late January and can last until early April, with the most intense pollution occurring in February and March. Factors like the amount of rainfall, wind patterns, and temperature shifts all influence the season's severity. If the region experiences dry conditions, the burning intensifies, prolonging the haze. Conversely, if early rains fall, the smoke can dissipate more quickly.

As a visitor, you may even notice the haze as soon as you descend into Chiang Mai, as I did. I could see the thick “blanket” of smoke as my plane began its descent into the valley, a clear indication of the air quality challenges below. For many tourists and residents, this visual reminder is their first introduction to smokey season.

The health risks

Smokey season presents a significant health risk, particularly due to the fine particulate matter (PM2.5) released into the air from the burning. These tiny particles are small enough to penetrate deep into the lungs and bloodstream, increasing the risk of respiratory issues, heart disease, and other health problems. The World Health Organization considers prolonged exposure to PM2.5 to be a serious health hazard.

However, the extent to which individuals are affected by smokey season varies. Some people, particularly those with pre-existing conditions such as asthma or other respiratory issues, may experience severe symptoms, including difficulty breathing, coughing, and eye irritation. Others may find the smoke to be more of a nuisance, experiencing minor discomfort like dry eyes or a scratchy throat. Children, the elderly, and pregnant women are also more vulnerable to the health effects of poor air quality.

Why Chiang Mai is so affected

Chiang Mai’s unique geography exacerbates the effects of smokey season. As the city lies in a valley surrounded by high mountains, the smoke from burning fields in the region gets trapped within the valley. Without strong winds to clear the air, the pollution lingers for days or even weeks. Other regions in Northern Thailand, as well as parts of Laos and Myanmar, experience similar issues during this time, but Chiang Mai tends to be one of the hardest hit due to its topography.

What can be done?

If you find yourself in Chiang Mai during the smokey season, there are steps you can take to minimize the health risks:

  • Check air quality regularly: There are several apps and websites that provide real-time air quality updates, including AQI (Air Quality Index) levels. Staying informed can help you decide when to limit outdoor activities.
  • Stay indoors: On days when the AQI levels are dangerously high, it’s best to stay indoors as much as possible. If you do need to go outside, limit strenuous activities like jogging or hiking.
  • Use air purifiers: If you’re staying in Chiang Mai for an extended period, investing in a good-quality air purifier for your accommodation can help reduce indoor air pollution.
  • Wear a mask: High-quality masks, such as N95 respirators, are effective at filtering out PM2.5 particles. Wearing one when you’re outside can significantly reduce your exposure to harmful pollutants.
  • Plan your visit: If possible, try to avoid visiting Chiang Mai during the smokey season. November through January is typically the best time to visit, with cool weather and clear skies.

Smokey season is an unfortunate reality for Chiang Mai and much of Northern Thailand, driven primarily by agricultural practices and exacerbated by geographic and climatic factors. While local governments and international organizations are exploring alternative solutions to reduce the reliance on slash-and-burn farming, the practice remains deeply ingrained in the region’s rural communities. For residents and visitors alike, being aware of the risks and taking precautions can help mitigate the health effects during this challenging time of year.