Frequency Analysis for the Estimation of Annual Maximum Three-Hourly Rainfall at Don Mueang International Airport

Abstract

Background and Objectives: Flood events occurring throughout numerous regions of Thailand have engendered considerable detriment to human life, private property, and the broader national economy. Regions of pronounced economic importance, most notably airport facilities, have been rendered incapable of sustaining normal operations, thereby precipitating flight delays and, in the most severe instances, the cancellation of scheduled services. The Aeronautical Meteorological Division of the Thai Meteorological Department, functioning as a governmental entity, is principally charged with the observation and reporting of meteorological conditions at aerodromes, the provision of aviation weather forecasts, and the issuance of advisories pertaining to meteorological phenomena deemed hazardous to aviation, in conformity with the regulatory frameworks promulgated by the World Meteorological Organization (WMO) and the International Civil Aviation Organization (ICAO). These functions collectively serve to support the provision of Air Navigation Services, with the overarching objective of ensuring operational safety and maximal efficiency. Notwithstanding the foregoing, the prevailing operational framework remains deficient in informational resources requisite for the effective management of water at airport facilities. In light of the aforementioned considerations, substantive scholarly interest has emerged regarding the estimation of maximum rainfall magnitudes, with particular emphasis on airport environs, with a view to elucidating the characteristics of maximum rainfall occurrence and to identifying an appropriate analytical model for its estimation. The findings of such an investigation are anticipated to furnish supporting information to stakeholders within the aviation industry and to meteorologists engaged in the practice of aeronautical meteorology and are further intended to inform prospective developments in the provision of aeronautical meteorological information services under the purview of the Aeronautical Meteorological Division, Thai Meteorological Department.

Methodology: Three-hourly rainfall data were collected from January 1981 to December 2024. The collected rainfall data were compiled and organized into a hydrological dataset. For each year of record, only the single highest three-hourly rainfall value was retained, in accordance with the recorded observation times, in order to construct an Annual Maximum Series. As a result, the Annual Maximum Three-Hourly Rainfall series for Don Mueang International Airport over the period January 1981 to December 2024 consists of exactly one value per year, yielding a total of 44 data points corresponding to the 44-year period of record. Subsequently, the probability of exceedance and the associated return period were determined, together with the frequency factors corresponding to each candidate probability distribution considered in the frequency analysis. The rainfall values estimated from each distribution were then computed, and the goodness-of-fit of each distribution was evaluated by means of the Chi-square test at a significance level of α= 0.05, in order to identify the probability distribution that most appropriately represents the observed rainfall data. In the final step, a regression equation relating the rainfall values estimated from the best-fit probability distribution to their corresponding return periods was derived. This equation provides the basis for estimating the Annual Maximum Three-Hourly Rainfall of Don Mueang International Airport at a specified return period.

Main Results: The occurrence of the Annual Maximum Three-Hourly Rainfall, when classified by month, showed that such rainfall occurred from March to December, occurring most frequently in September. When classified by observation time, the rainfall occurred at observation times ranging from 0700 hours (cumulative rainfall recorded from 04:00 to 07:00) through 0400 hours (cumulative rainfall recorded from 01:00 to 04:00), occurring most prominently at the 1900-hour observation time (cumulative rainfall from 16:00 to 19:00) and the 2200-hour observation time (cumulative rainfall from 19:00 to 22:00). When classified by day-of-month period, the rainfall occurred most frequently during days 21–31 of the month, followed by days 11–20 of the month. When the goodness -of-fit test was conducted using the Chi-square test at a significance level of 0.05, the Log-Pearson Type-III Distribution was found to be the most appropriate probability distribution for estimating the Annual  Maximum Three-Hourly Rainfall at Don Mueang International Airport (p > 0.05). The regression equation for estimating the rainfall value at a given return period is:     where  denotes the estimated Annual Maximum Three-Hourly Rainfall (mm), and   represents the return period (years). The estimated rainfall values were 54.51 mm at a return period of 1.02 years, 99.98 mm at a return period of 10 years, and 145.85 mm at a return period of 100 years.

Conclusions: The occurrence of the Annual Maximum Three-Hourly Rainfall was found to span from March to December, occurring most prominently in September. When classified by observation time, the rainfall occurred most prominently at the 1900-hour and 2200-hour observation times. When classified by day-of-month period, the rainfall occurred most prominently during days 21–31 of the month, followed by days 11–20 of the month. The probability distribution most appropriate for estimating the rainfall of Don Mueang International Airport.