An obviously increasing trend of torrential rains in Taiwan has emerged in recent years. The frequency of extreme downpours in which hourly rainfall exceeds 100 millimeters has also greatly increased, particularly during periods with prevailing southwesterly air currents. The region comprising Tainan County, K a o h s i u n g C o u n t y a n d P i n g t u n g C o u n t y h a s
experienced a relatively high frequency of torrential downpours. These types of environmental changes not only make the job of weather forecasting more difficult; they create enormous pressure for the need to adjust disaster prevention and rescue measures.