Turning up the heat in Jakarta

dward McMillan, Jakarta

Think of the difference between reclining in a hammock under a shady tree and standing in the full glare of the noon-day sun. That, in a nutshell, is how much Jakarta's climate has changed over the past fifty years. Jakarta is now, year-round, hotter than mid-summer Cairo -- and, at the current rate, looks set to overtake even summertime Mumbai in the heat stakes by 2020.

Jakarta is undergoing its very own version of global warming, driven by the frenetic commercial activity it's home to and by the relentless removal of trees and vegetation. And there is good reason to worry about the consequences.

The most immediate threat, and one that Jakarta can barely cope with even now, is flooding. Warmed city air tends to rise, funneled upwards along "urban canyons" like Jalan Sudirman: The result is cloud formation and enhanced rainfall.

In Atlanta, a city that suffers from warming so marked that residents now refer to it as "Hotlanta", the higher urban temperature is believed to increase summer rainfall by as much as 20 percent in a broad area downwind of the city. The number of days of heavy precipitation recorded in Ankara, Turkey, is half as many again as in neighboring rural areas -- with weekdays experiencing heavier rain than weekends, when commuters tend to keep to the suburbs.

There is little evidence that Jakarta's total annual rainfall has increased since 1950. However -- and this is what is critical from a flooding perspective -- the type of rainfall has changed. Steady drizzles, of the kind that can be absorbed and dissipated by the city's drains and rivers, are now less common. In their place have come storms that deposit large quantities of rain in a matter of minutes, overwhelming the city's drainage systems and bringing traffic chaos.

Consider also the effect of higher temperatures on Indonesia's energy consumption. For every one-degree Celsius increase in temperature, the peak electricity load in a city the size of Jakarta increases by approximately 3 percent as residents reach for the air-conditioning. That spells bad news for a government already grappling with an energy crisis.

And if you think air quality is bad now, just wait: the photochemical reactions that produce smog thrive in warmer conditions. In the Los Angeles basin, an increase in temperature of just half a degree translates into an overall increase in smog of about 2 percent. That may not sound a lot, but transpose it to Jakarta -- which experiences just 25 days of "good" air quality per year as it is, and where vehicle emissions are growing by 5 percent each year -- and the public health consequences could be significant.

Jakarta's predicament is, in large part, attributable to the city itself. Trees and vegetation block incoming sunlight and cool the air by evaporation of moisture through leaves. Replace them with the Jakartan staples of concrete and asphalt (which absorb a greater fraction of the sun's rays) -- and, for good measure, erect large malls and office complexes that block night- time cooling -- and the result is runaway climate change.

Climatologists have a name for such warming -- the "urban heat island effect" -- and Jakarta isn't alone in experiencing it. East-coast North American cities are, on average, 1.5 degrees Celsius warmer than surrounding rural areas. Downtown Barcelona is typically 3 degrees Celsius warmer than its neighboring countryside. And Beijing's heat island now covers 200 square kilometers and occasionally produces a sweltering 6 degree Celsius temperature uplift.

The widespread occurrence of heat islands points to an obvious conclusion: They are unavoidable. Jakarta's warming is a natural consequence of the urban growth that provides housing and jobs to its ever-burgeoning population.

However, policy solutions do exist to mitigate its impact. Planting trees serves simultaneously to provide shade and to increase the city's flood-absorption capacity. The Singaporean government has been actively investigating the potential of "sky- rise gardens" on apartment blocks to perform just this role, with promising results.

And Jakarta's authorities could cut the heating effect of future suburban sprawl by up to one-fifth at a stroke by requiring new houses to have light-colored (white or terracotta red) roofs, which absorb much less sunlight than their darker- colored counterparts.

These are easily-implemented, low-tech solutions to a pressing problem. Twenty-first century Jakarta need not become an urban hothouse -- but, if left unchecked, it surely will.

The writer is a freelance British writer living in Jakarta.