Rapid population growth and global warming are increasing exposure to extreme heat in cities, aggravating health problems and making moving to urban areas less beneficial for the world’s poor, according to a new study.
The rise is affecting nearly a quarter of the world’s population, said the report published in the Proceedings of the National Academy of Sciences.
In recent decades, hundreds of millions of people have moved from rural areas to cities where temperatures are generally higher because of surfaces such as asphalt which trap heat and a lack of vegetation.
Scientists studied the maximum daily heat and humidity in more than 13,000 cities from 1983 to 2016.Using the so-called “wet-bulb globe temperature” scale, a measure that takes into account heat and humidity, they defined extreme heat as 30 degree Celsius(86 degree Fahrenheit).
The researchers then compared weather data with statistics on the cities’ population over the same 33-years period. They calculated the number of days of extreme heat in a particular year by the population of the city that year to come up with a definition called person-days.
The authors found that the number of person-days in which city dwellers were exposed went from 40 billion in 2016
Cascade Tuholske at Colombia University’s Earth Institute, a lead author of the study, said the rise “increases morbidity and mortality.”
“It impacts people’s ability to work, and results in lower economic output. It exacerbates pre-existing health conditions,” he said in a statement.
Population growth accounted for two-thirds of the exposure spike, with actual warming temperatures contributing a third, although proportions varied from city to city, they wrote.
Last decades, new records were set in the world for tornadoes, drought, wind, floods, wildfires and hot temperatures, testifying unusual weather and climate patterns with increasing frequency and intensity of extreme weather event. Extreme heat events are natural hazards affecting many regions in the world, nevertheless limited work has been done on the analysis and affects of extreme heat events in Africa.
Between 1981 and 2016 there are marked areas of drying in pars of northeast and much of southern Tanzania, In contrast, moderate wetting trends occurred in Central Tanzania and stronger wetting trends in northwest of the country. A clear warming trends is apparent in annual temperature. By the 2090s projected warming is in the range of 1.6 to 5,0 degree Celsius.
Climate change impacts of severe droughts, floods, livestock deaths, crop failures and outbreak of disease(such as cholera and malaria) are likely to be regularly observed.