Estimation of regional intensity-duration-frequency relationships of extreme rainfall by simple scaling in Thailand

In 2022, Thailand was subjected to extensive flooding all over the country in both urban and rural areas, which caused tremendous losses. Better design and construction of infrastructures for timely and sufficient drainage can help mitigate the problems. This requires accurate intensity-duration-frequency (IDF) relationships at or near the problem areas. To obtain an IDF curve, a continuous rain record from an automatic gauge of the area is needed. Some automatic rain-gauge stations are scattered all over the country and are much fewer in number than the daily-reading rain-gauge stations. By applying a simple scaling theory, we can construct IDF curves from the daily rain records. The 37 automatic stations distributed the scaling exponent over the country. Gumbel location and scale parameters, from 30-year rainfall records, were determined. These three parameters were mapped throughout the country and are ready to be used for creating an IDF curve at any location in the country. We verified these parameters to generate IDF curves for three sites in different regions and found very good agreements. The majority of the errors were less than 15%.