Using the concept of area reduction factor to explore the probable maximum flood of shimem reservoir

In recent years, rainfall records indicate the tread on concentrating and intensifying of rainfall pattern under climate change in Taiwan. This study investigates whether original design flood is still applicable in current weather condition for the Shimen reservoir in Taiwan. Estimation of average regional rainfall is the basis for designing and planning in water resource. A scheme is proposed to convert a point rainfall to the areal rainfall. By introducing the idea of the area reduction factor, the maximum precipitation recorded at all rainfall gauging stations was first multiplied by the area reduction factor 0.7, in the Shimen reservoir case, to obtain the Maximum Probable Precipitation (PMP). Then PMP was multiplied by the area to obtain the Maximum Probable Flood (PMF). The area reduction factor, which is related to the size of watershed area, is capable of addressing the areal properties. PMP and PMF were estimated to be 1175.8 mm and 15675.5 cm, respectively. These values are greater than the current design-flood of Shimen Reservoir, which provides estimation suggestion for further security review.