Analysis of maximum precipitation in Thailand using non‐stationary extreme value models

Non‐stationarity in heavy rainfall time series is often apparent in the form of trends because of long‐term climate changes. We have built non‐stationary (NS) models for annual maximum daily (AMP1) and 2‐day precipitation (AMP2) data observed between 1984 and 2020 years by 71 stations and between 1960 and 2020 by eight stations over Thailand. The generalized extreme value (GEV) models are used. Totally, 16 time‐dependent functions of the location and scale parameters of the GEV model are considered. On each station, a model is selected by using Bayesian and Akaike information criteria among these candidates. The return levels corresponding to some years are calculated and predicted for the future. The stations with the highest return levels are Trad, Samui, and Narathiwat, for both AMP1 and AMP2 data. We found some evidence of increasing (decreasing) trends in maximum precipitation for 22 (10) stations in Thailand, based on NS GEV models. Non‐stationarity in heavy rainfall time series is often apparent in the form of trends because of long‐term climate changes. We have built non‐stationary models for annual maximum daily (AMP1) and 2‐day precipitation (AMP2) data by 79 stations over Thailand. The generalized extreme value (GEV) models are used. Totally, 16 time‐dependent functions of the location and scale parameters of the GEV model are considered. On each station, a model is selected by using Bayesian and Akaike information criteria among these candidates. The return levels corresponding to some years are calculated and predicted for the future. The changes of 50‐year “conventional” return levels of AMP1 over Thailand in the years 1990, 2020, and 2050 in which the NS models were selected by BIC. The extreme rainfall in the northwest region, including Mae Sa Riang, and in the northeast region, including Maha Sarakham, is increasing. Whereas maximum precipitation in the central region, including Lop Buri and Phitsanulok, and in Nakon Phanom in the northeast region is decreasing. Downpour in the southeast region, including Nakon Si Thammarat and Narathiwat, is increasing with very heavy precipitation.