Tsukuba, Japan – In a groundbreaking study led by researchers at the University of Tsukuba, advanced numerical modelling has provided critical insights into Colombo’s escalating heatwave crisis. For the first time, cutting-edge simulation technology has been applied to analyse how rapid urbanisationcontributes to extreme heat in Sri Lanka’s capital. As climate change accelerates, heatwaves become more frequent and intense, posing significant challenges to public health, urban infrastructure, and daily life. The study highlights the increasing severity of heatwaves in Colombo using high-resolution weather prediction models. It underscores the urgent need for updated urban planning and heat mitigation strategies to protect vulnerable communities in tropical cities.
Heatwaves on the Rise in Colombo
A heatwave is a prolonged period of excessively high temperatures that can have severe consequences for human health, energy consumption, and the overall quality of life in a city. While Sri Lanka’s Meteorological Department has not yet provided an official definition of heatwaves, scientists often use percentile-based thresholds to classify extreme temperature events. In this study, researchers applied one of the most widely accepted heatwave definitions, where a heatwave is identified when:
= The daily maximum temperature exceeds the 97th percentile for at least three consecutive days.
= The daily maximum temperature remains above the 81st percentile throughout the period.
= The average daily maximum temperature during the event is above the 97th percentile.
The team identified three severe heatwave cases between 2020 and 2022, defined using percentile thresholds: temperatures exceeding the 97th percentile (33.8°C) for three consecutive days, with averages above the 81st percentile (32.6°C). These metrics, aligned with global standards, highlight a clear trend that Colombo’s heatwaves are growing hotter and longer. These heatwaves, with maximum temperatures exceeding 35°C, highlight an alarming trend that heatwaves in Colombo are becoming longer, more frequent, and more intense.
How Advanced Simulations Help Us Understand Heatwaves
This study, conducted in Japan using highly sophisticated numerical models, has provided valuable insights into Colombo’s urban thermal environment. The research utilised the Weather Research and Forecasting (WRF) model, an advanced atmospheric model widely used for weather prediction and climate studies. To improve the accuracy of heatwave simulations, the model was coupled with the Single-Layer Urban Canopy Model (SLUCM), which captures how urban structures like buildings, roads, and green spaces influence temperature and airflow.
A key innovation in this research was using high-resolution Land Use and Land Cover (LULC) data. Instead of relying on outdated global datasets, the researchers incorporated advanced Esri Sentinel-2 land-use data, which provides an incredibly detailed representation of Colombo’s urban landscape at a 10-meter resolution. Using this dataset, the simulations more accurately captured the effects of rapid urbanisation, changes in land cover, and heat-retaining infrastructure on local temperatures.
Findings: How Colombo’s Urban Growth is Intensifying Heatwaves
The study revealed several critical findings about Colombo’s heatwave dynamics:
= Urban areas in Colombo are significantly hotter than surrounding regions – During heatwaves, daytime land surface temperatures (LST) in urban areas often exceed 45°C. In comparison, nighttime temperatures remain above 30°C, particularly in commercial zones.
= Coastal regions experience a cooling effect – Compared to the urban core, coastal areas record lower temperatures, with daytime LSTs between 40-45°C and night-time temperatures between 25-30°C. This is likely due to the influence of the sea breeze, which provides some natural cooling.
= High-resolution land-use data improve heatwave prediction accuracy – The advanced Esri Sentinel-2 dataset significantly reduced temperature prediction errors, improving the accuracy of numerical models in representing Colombo’s urban heat environment. The study found that high-resolution LULC data reduced daytime temperature anomalies by up to 2.5°C and night-time anomalies by 1.0°C compared to coarser datasets.
= Urbanization worsens heatwave impacts – The expansion of built-up areas, mainly replacing green spaces with concrete and asphalt, exacerbates Colombo’s urban heat island effect. The study found that commercial and high-density residential zones experience the highest night-time temperatures, making heat stress a growing concern for residents.
Why This Research Matters for Society
The increasing frequency and severity of heatwaves pose significant risks for public health, especially for vulnerable populations such as older people, children, and outdoor workers. Studies have shown that prolonged exposure to extreme heat can lead to dehydration, heat exhaustion, and even life-threatening heat strokes. Furthermore, higher temperatures increase electricity demand for air conditioning, leading to power shortages and rising energy costs.
This study provides a scientific foundation for developing effective heat mitigation strategies. By understanding how urban landscapes influence temperature distribution, city planners and policymakers can take proactive measures to combat extreme heat, including:
= Expanding green spaces – Parks, urban forests, and rooftop gardens can help cool down city temperatures.
= Implementing cool roofs and reflective surfaces – Using heat-reflective materials in buildings and roads can reduce heat absorption.
= Enhancing coastal ventilation – Protecting and maintaining open coastal areas can help maximise the cooling effects of the sea breeze.
= Promoting climate-resilient urban planning – Regulations should encourage sustainable development that minimises heat-retaining infrastructure.
Looking Ahead: A Call for Action
Colombo’s rising heatwave trends are a warning sign of climate change and urbanisation reshaping the city’s thermal environment. This study, conducted using cutting-edge numerical models in Japan, has provided critical insights into the impact of high-resolution land-use data on heatwave prediction accuracy.
As heatwaves become increasingly pressing, governments, city planners, and researchers must collaborate on developing effective adaptation and mitigation strategies. This research is not just an academic exercise, it has real-world implications for improving public health, reducing energy consumption, and making Colombo a more liveable city in the face of extreme climate events.
With continued advancements in climate modelling and data analysis, we now have the tools to anticipate and address the growing heat risks in Colombo and other tropical cities. The time for action is now, our cities must be designed with resilience in mind, ensuring a sustainable and comfortable environment for future generations.
By Dr. K.L. Thisara Sathsara
Lecturer, Department of Geography
University of Sri Jayewardenepura.
Prof.Hiroyuki Kusaka
Center for Computational Sciences,
University of TsukubaJapan
Full article: https://link.springer.com/article/10.1007/s00704-024-05242-9#citeas
