Sun, Aug 23, 2009 - Page 8 News List

Data from the sea can assist our predictions

By Liu Cho-teng 劉倬騰

Typhoon Morakot brought two to three days of extremely heavy rainfall over the southern and central parts of Taiwan, causing calamitous floods. Some people blame the disaster on inadequate water management, while others say that Taiwan’s weather forecasts are unreliable; in both cases more investment is said to be required. There is truth in both arguments, but what is actually lacking?

Typhoons in the Pacific and hurricanes in the Atlantic cause damage mostly in the form of floods, landslides and burst dykes. When a typhoon approaches, meteorologists can forecast strong wind and heavy rain, but all natural phenomena are inherently uncertain, unstable and unpredictable.

Hurricane Katrina, which struck the south coast of the US in 2005, is a good example. It quickly picked up power as it passed over an unusually warm loop current in the Gulf of Mexico, making it more powerful than meteorologists had predicted. By then it was too late to evacuate everyone, resulting in a disaster on a scale that occurs only once or twice a century in the US.

The great majority of hurricanes and typhoons derive their power from the warmth of the ocean. Typhoons that hit Taiwan draw warmth and water vapor from the surrounding waters. If the sea is abnormally warm, it will supply the gathering storm with more water vapor and power, often generating super-typhoons that carry extremely heavy rainfall.

In 2001, Typhoon Nari circled for a long time above the Kuroshio — the Japan Current — before attacking Taiwan from the direction of Okinawa. The extremely heavy rainfall paralyzed transport in and around Taipei and halted operations of most of the Banqiao-Nangang Line of Taipei’s MRT system for more than two months.

The cloud bands brought by Typhoon Morakot basically followed the Kuroshio Current from the South China Sea. As these clouds slowly crossed Taiwan in the wake of the typhoon, they drew in more and more humidity from the South China Sea, generating extremely heavy rainfall in southern and central Taiwan and causing serious flooding.

The US is a continental nation rather than a maritime one, but it has a National Oceanic and Atmospheric Administration dedicated to management of information about the sea and the weather. Even with such a specialized body in existence, the US has on occasions failed to process and apply all available information in time to avert disaster.

Taiwan, which has no central maritime administration or ministry, has even less chance of obtaining timely and comprehensive information about maritime conditions, so our typhoon forecasts are even more limited in their accuracy.

There’s a joke about people who looked for a lost key but did not find it because they only looked where there was light, and not in the dark — which is where the key was lost.

The solution to finding the key is to illuminate the place where it was lost. Warm ocean water is what lies behind the formation of typhoons, and it is the cause of super-typhoons and super-heavy rainfall. Without this crucial item of information about the sea, how can Taiwan’s ability to forecast typhoons possibly be improved?

Meteorologists say we need more funding to improve typhoon forecasts, and I agree with them. Even if we use just a little funding to “illuminate” and look for the “key” — essential data from the ocean — then we can use this data to greatly improve our forecasting of powerful typhoons and super-heavy rainfall.

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