The hidden dangers of rising nighttime temperatures in Bangladesh

Climate change is no longer a distant threat; it is a reality affecting lives today. While much attention is given to scorching daytime heatwaves and extreme weather events, an equally insidious problem remains largely unaddressed—rising nighttime temperatures (minimum temperature).

In Bangladesh, where climate vulnerability is already a major concern, warming nights are silently disrupting agriculture, human health, and ecosystems. This issue demands immediate recognition and action.

Scientific data reveals that nighttime temperatures are increasing at a faster rate than daytime temperatures in many parts of the world, including Bangladesh.

This phenomenon is primarily driven by rising greenhouse gas emissions, which trap heat and reduce the cooling effect that nightfall traditionally brings. Urbanization, deforestation, and changes in land use further intensify this warming trend, particularly in rapidly growing cities such as Dhaka and Chattogram.

According to Bangladesh's National Adaptation Plan (NAP) for 2023–2050, the country has experienced a discernible warming trend over recent decades. Both minimum (Tmin) and maximum (Tmax) temperatures have shown increasing patterns, with Tmin (nighttime temperatures) rising more rapidly than Tmax (daytime temperatures).

This trend has led to a decrease in the diurnal temperature range (DTR), which is the difference between daytime highs and nighttime lows. A reduced DTR can have significant implications for agriculture, human health, and natural ecosystems. 

Looking ahead, the NAP projects that both Tmin and Tmax will continue to rise throughout the 21st century. Under high-emission scenarios, such as RCP8.5, the mean annual Tmax is expected to increase by approximately 1.75°C in the near future (2021–2060) and by about 3.85°C in the far future (2061–2100).

Similarly, the mean annual Tmin is projected to rise by around 1.85°C in the near future and by approximately 4.07°C in the far future. These increases are anticipated to be more pronounced during the winter months, with the northern and northwestern regions of Bangladesh experiencing the most significant temperature escalations. 

Agriculture forms the backbone of Bangladesh’s economy, and staple crops like rice are highly sensitive to temperature fluctuations. Scientific studies indicate that for every 1°C increase in nighttime temperature, rice yields can decline by up to 10%. Unlike daytime heat, which plants can sometimes withstand with adaptive responses, warmer nights disrupt their natural respiration processes, leading to lower grain production and compromised quality.

Boro rice, a dry-season crop, is particularly vulnerable. As nighttime temperatures rise, plant respiration rates increase, leading to higher energy expenditure and lower carbohydrate accumulation. This results in lighter grains and overall reduced yields. Additionally, rising temperatures contribute to increased water demand, further straining limited irrigation resources. Livestock farming, another key sector in Bangladesh, is also affected as heat-stressed animals produce less milk and suffer from reproductive issues.

Beyond agriculture, rising nighttime temperatures pose severe health risks. The human body relies on cooler nights to recover from daytime heat. Prolonged exposure to high nighttime temperatures can lead to heat stress, sleep disturbances, and an increased risk of cardiovascular diseases. Vulnerable groups—including the elderly, children, and those with pre-existing health conditions—are particularly at risk.

In cities like Dhaka, where high population density and poor ventilation make it difficult for heat to dissipate, the impacts are even more pronounced. Informal settlements, where many lack access to electricity and cooling systems, experience prolonged exposure to unbearable heat, leading to rising mortality rates during heatwaves. The growing demand for air conditioning and fans also places additional pressure on Bangladesh’s already strained energy grid.

Bangladesh’s ecosystems are also under threat. Many species rely on diurnal temperature variations for their biological functions. Warmer nights can disrupt breeding cycles, migration patterns, and predator-prey relationships.

The Sundarbans, the world's largest mangrove forest, is already experiencing ecological stress due to rising temperatures and salinity intrusion. Additionally, disease-carrying mosquitoes, which thrive in warm and humid conditions, are becoming more active, contributing to the increased prevalence of vector-borne diseases such as malaria and dengue. The country has witnessed record-breaking dengue outbreaks in recent years, highlighting the connection between warming temperatures and public health crises.

While Bangladesh faces unique challenges, it can draw inspiration from strategies employed by other nations to combat rising nighttime temperatures. Singapore has successfully cooled parts of its city by planting over 7 million trees and creating more than 300 parks and gardens. This increase in green cover provides shade, facilitates evapotranspiration, and enhances urban aesthetics, collectively reducing ambient temperatures.

In the United States, cities like Los Angeles have implemented cool roof programs, encouraging residents to install reflective roofing materials that reduce heat absorption. This approach helps lower indoor temperatures and decreases energy consumption for cooling.

Traditional architectural designs in the Middle East incorporate features such as wind towers and thick walls to promote natural ventilation and reduce indoor temperatures without relying on electricity. These passive cooling methods can be adapted to modern buildings to enhance thermal comfort.

Ahmedabad in India has developed a comprehensive Heat Action Plan that includes early warning systems, public awareness campaigns, and the establishment of cooling centers to protect vulnerable populations during heatwaves. This proactive approach has been effective in reducing heat-related illnesses and fatalities.

Bangladesh has been at the forefront of climate resilience efforts, yet nighttime warming requires more focused policies and strategies. Immediate steps must include expanding green spaces, implementing rooftop gardens, and adopting reflective roofing materials to help mitigate urban heat retention. Investing in heat-resistant rice and wheat varieties, promoting alternative farming techniques, and improving irrigation efficiency will be key. Establishing heatwave early warning systems, increasing access to cooling centers, and launching community-based education campaigns on heat safety can protect vulnerable populations. Encouraging solar and other sustainable energy sources can help manage the rising demand for cooling while reducing dependency on fossil fuels. Bangladesh must incorporate nighttime warming trends into its national climate adaptation policies to ensure comprehensive preparedness for future challenges.

As global climate change accelerates, rising nighttime temperatures in Bangladesh must not be ignored. The country has already shown remarkable resilience in the face of climate threats, but more targeted efforts are needed to address this silent crisis. Without immediate action, the combined effects on agriculture, health, and ecosystems could severely impact the nation’s future.

Bangladesh has the opportunity to be a leader in tackling nighttime warming through innovative solutions and robust policymaking. The time to act is now—before the silent threat becomes an irreversible disaster.

This Article was written by Dr. Mohammad Kamruzzaman Milon; Senior Scientist and Agri-climate Expert, Bangladesh Rice Research Institute