ASSESSMENT OF MAXIMUM HAIL SIZES AND THEIR VALUE AT A 100-YEAR RETURN PERIOD

Hailstorms are relatively rare phenomena in Viet Nam, and understanding their characteristics is crucial for assessing the potential impact of hail events on various sectors. This study explores the maximum hailstone sizes observed in Viet Nam from 1961 to 2021 and uses the Gumbel distribution to estimate hailstone sizes at different return periods. Hail events in Viet Nam occur infrequently, with a common occurrence rate of less than once per year. However, some regions in the North, especially in the mountainous areas of the NorthWestern region, experience hail events approximately 1 - 2 times per year. The study records the largest hailstone sizes observed during the research period, with notable examples including 12 cm at the Bac Ha station and 10 cm at the Chiem Hoa station. These sizes exceed the calculated values for a 100-year return period, emphasizing the need for further research and preparedness. Despite the limited dataset of hailstone measurements, the Gumbel distribution is found to be a useful tool for estimating hailstone sizes at a 100-year return period. The theoretical estimates closely align with the observed values. At a 15-year return period, the most common maximum hailstone sizes range from approximately 1 - 3 cm, while at a 100-year return period, prevalent maximum hailstone sizes vary from 2.5 to 5.0 cm.