How to pick up the heavy rainfall of the typhoon? Zhang Liqiu's team established a flood forecasting system, which was recognized internationally.

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The time of rainfall in Taiwan is concentrated from the rainy season to autumn, but abundant rainfall comes all of a sudden, so it is not easy to "connect and fill up" smoothly, especially when typhoons are heavy rainfall for a short time. In the past, reservoir personnel can only rely on experience to turn on and off the sluice gates and adjust the water level in the wind and rain to maximize the efficiency of the reservoir. Each typhoon is like a battle of wits between reservoir personnel and nature.

In order to regulate the water situation more accurately, Zhang Liqiu, a professor in the Department of Water Resources and Environmental Engineering at Tamkang University, built a flood forecasting system based on 50 years of typhoon data from the Shimen Reservoir. "as soon as the typhoon path and total rainfall are predicted, the total time of flood and flood peak will be known instantly." After six years of practical practice, it has been proved that the system can successfully improve the accuracy of flood early warning and the effect of water resources management, and has been published in the international well-known journal Nature Communications.

Zhang Liqiu (Photo _ Lin Yijun), a professor in the Department of Water Resources and Environmental Engineering at Tamkang University and director of the Water Environment Information Research Center, has been working on water conservancy works for thousands of years, bringing typhoons that Rain Water has also brought the test.

"typhoons every year are both anticipated and stressful." Zhang Liqiu said that for farmers, the adequacy of reservoir water is related to agricultural production. The largest source of water in Taiwan's reservoirs comes from torrential rains brought by typhoons, and the accuracy of reservoir flood forecasting is the key information for reservoir flood control and water storage.

However, the uncertainty of typhoon path and rainfall is high, and each typhoon is a test for reservoir personnel. "the goal of reservoir workers is to be able to fill up after a typhoon, so they have to release water before a typhoon. The difficulty lies in how much water has to be released and when it will be just right."

Flood discharge before rainfall is very important. If the heavy rain exceeds the reservoir capacity and causes overflow, the dam structure will be damaged. Therefore, flood discharge must be done first to ensure the safety of the dam. Zhang Liqiu said that water discharge can only be made up by rainfall. If there is any error, it will be related to downstream water use. However, there was no accurate prediction system in the past, and reservoir control personnel can only judge rainfall and water level based on experience or calculation. Therefore, the reservoir staff are under great pressure.

Flood discharge from Shimen Reservoir (Photo Source: North District Water Resources Bureau, Water Conservancy Department, Ministry of Economic Affairs) Typhoon data of Shimen Reservoir in the past 50 years, a flood forecasting system is established through path and rainfall analysis.

Zhang Liqiu took the plan of Xiabei District Water Resources Bureau in 102 to carry out the flood forecasting system of Shimen Reservoir during typhoon period. for this reason, he collected the relevant data of more than 90 typhoons from 1965 to the present. And cooperate with Professor Zhang Feizhang of the Department of Bio-Environmental Systems Engineering of National Taiwan University to refine and improve the forecasting system.

The prediction system built by Zhang Liqiu analyzes the typhoon tracks and rainfall over the past 50 years. She shows one of the track analysis maps, cutting the whole map into small grids and marking the typhoon area with different shades of color. the darker the color is, the greater the impact on the Shimen Reservoir, and the different paths are classified, such as north platform, piercing platform, and so on.

Zhang Liqiu explained that the biggest feature of this system is that the path is vectorized, which is more suitable for classification than analogy or digital coordinates. "plane coordinates will have two dimensions (horizontal and vertical in both directions), and the vector will convert the two dimensions into one direction." this makes the analysis much easier. "

For different typhoon tracks, the darker the grid color, the greater the impact on Shimen Reservoir (photo source _ "Natural Communications" Nature Communication)

The classification results of historical typhoon tracks (photo source _ "Natural Communication" Nature Communication) are applicable to different duration of rain and different rainfall. Input typhoon path and total rainfall to predict flood course immediately.

Zhang Liqiu said that the precipitation conditions are different when different typhoons occur, including the rainfall and the total rainfall time, which will affect the flood size and the arrival time of the flood peak. "it must be converted into a flow characteristic curve before it can be easily predicted."

Zhang Liqiu explained that the so-called flow characteristic curve is to first present the total rainfall time and peak time of all typhoons as a percentage, so that there is no problem of different typhoon duration. "Typhoon A has three days. Typhoon B has a total rainfall of 400 mm in two days, and the total rainfall is 300 mm. If all the time is converted into a percentage, the two typhoons can follow the flow characteristic curve. Automatically make a full flood forecast. "

In other words, by mastering the characteristic curve, we can apply different types of rainfall through the prediction path, and then we can follow the rainfall situation, for example, the maximum rainfall will be reached in a few hours, and the whole flood forecast is to predict the rainfall caused by typhoon. The process from small to large and then to gradual.