The Impact Of Global Warming On Rainfall And Flooding.

"Breaking news in recent years has been swamped with stories of extreme weather - flash floods in East Asia, prolonged drought in Africa, destructive hurricanes like Hurricane Katrina, heavy monsoon rainfall in South Asia, and an historic heat wave in Europe. The effects of these weather crises have been devastating and their frequency seemingly on the rise." - A NASA Feb 2007 report

When i was a boy, the year-end monsoon season always started somewhere in late October and will end around February of the following year, followed by the hot months from March to September. But the timing of this raining season has become unpredictable and had in fact, shifted in recent years. Together with sudden occurrences of heavy thunderstorms in what is suppose to be hot months and hot days during the traditional monsoon period, it all points to changes to our weather patterns and i am sure these freakish climate changes are not isolated to my country alone.

Global warming, the result of unbridled emission of greenhouse gases into the atmosphere, leads to higher rainfall because a warming atmosphere contains more water vapour and more energy. An increase in global temperatures will cause an increase in evaporation and higher levels of water vapour. In addition, a warmer atmosphere is also capable of holding more water vapour. The excess water vapour will in turn lead to more frequent heavy and intense downpours which results in flooding, soil erosion, landslides and damage to structures and crops.

Besides causing increased rainfalls, global warming also leads to heavy flooding due to the impact of the massive amount of CO2 - the principle greenhouse gas - has on vegetation. During photosynthesis - the process in which plants make food and produce oxygen - CO2 enter plants thorough tiny holes in their leaves called stomata. Plants take water from the ground and secrete the excess thorough the stomata. But higher levels of CO2 in the air cause these tiny holes to open far less widely, leading to reduced water loss from the plants.

And with plants extracting less water from the soil in a warmer world, the soil becomes saturated and surplus water will then drain into rivers. "This will increase global flows by a further 6 per cent on top of the 11 per cent rise already predicted due to global warming," said a meteorologist at Britain's Met Office. Together with more water staying in the ground and the runoff into rivers, areas with increased rainfall will suffer severe flooding and flash floods.

According to recent study published by the British science journal Nature in Aug 2007, the risks of flooding may increase more than previously expected because intense precipitation events - heavy downpours - would be more likely to occur over areas with saturated ground.

Flooding is a major problem, especially in poor countries that do not have the money to invest in drainage systems to cope with runoffs from saturated soils. Since June this year, more than 3,200 people in South Asia have been killed as a result of heavy monsoon rains and snow melt and many more left homeless.

*Sources :
- NASA
- British science journal Nature
- Union of Concerned Scientists
- Climate Ark

*Related post : The Melting Of Our Polar Ice Caps.