Pagasa: More trees, lower heat index

Pagasa: More trees, lower heat index
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AN EXPERT from the state weather bureau in Mactan, Cebu said areas with more trees and vegetation tend to have lower heat indexes, indicating they are cooler compared to less green surroundings.

Weather specialist Jhomer Eclarino, from the Visayas Philippine Atmospheric, Geophysical and Astronomical Services Administration (Pagasa) Regional Services Division, said urbanized areas generally experience relatively higher heat indexes.

“More vegetation results in lower surface temperatures compared to urban or highly urbanized areas, where there are many buildings and cemented roads. The presence of more establishments leads to higher surface temperatures, contributing to the heat index,” he said.

Surface air temperature refers to the actual temperature of the air measured by a thermometer, while heat index takes into account both temperature and humidity to measure how hot it feels to the human body.

Evapotranspiration

According to the United States Environmental Protection Agency, trees and vegetation, including bushes, shrubs, and tall grasses, actively lower surface and air temperatures by providing shade and cooling through evaporation and transpiration, also known as evapotranspiration.

Through transpiration, trees and vegetation absorb water through their roots and cool their surroundings by releasing water vapor into the air through their leaves. This contributes to the reduction of heat.

Eclarino confirmed to SunStar Cebu on Friday, May 3, 2024, that the highest recorded heat index for Cebu this year was 40 degrees Celsius.

The figure is categorized under the extreme caution category, suggesting that heat cramps and heat exhaustion are possible, and further activity may result in a heatstroke.

Hotter in Cebu City

However, he said the heat index figure they announced for Cebu was recorded at their Pagasa station in Mactan Island.

“If you come here to our station in Pagasa Mactan, you can still see trees and some vegetation. So, if you compare it to Cebu City, which is surrounded by high-rise buildings, malls, and cemented roads, then probably the heat index there is higher than 40 degrees Celsius,” he said.

A national media outlet reported last April 19 that the Department of Environment and Natural Resources is advocating for the creation of urban green spaces to mitigate the rising high heat index in the country.

The report explained that heat can escape from soil, but in cities, where there is more cement, asphalt, and concrete than soil, heat is absorbed and trapped at the surface. This results in cities being significantly warmer than rural areas.

Green parks and forests offer natural shade and evaporative cooling, which help reduce the heat

Meanwhile, Pagasa continues to remind the public to adhere to the health and safety measures since they consider the month of May to have the hottest days of the year.

He said that last year, the highest heat index recorded in Cebu was 43 degrees Celsius on May 17, 2023.

Eclarino said Cebu first recorded the 40 degrees Celsius heat index in April, and with May being considered the hottest month, they anticipated a further increase in the heat index

He added that on May 31, 2010, also during the El Niño phenomenon, the province recorded its highest surface temperature at 37 degrees Celsius, with a heat index of 49 degrees Celsius.

Earlier, Dr. Eugenia Mercedes Cañal, regional epidemiologist from the Department of Health 7, urged the public to refrain from going outdoors between 9 a.m. and 4 p.m., particularly during peak hours when the heat index reaches its highest levels.

She recommended wearing sunscreen and staying hydrated by drinking plenty of water. / KJF

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