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Journal of Letters

Publication Date

2025-12-28

Abstract

This research aims to investigate and analyze spatial and temporal characteristics of daily rainfall which include rainfall amount, proportion of areas with heavy (35-90 mm/day) and extreme (>90 mm/day) rainfall intensity, numbers of extreme rainfall clusters, average size of extreme rainfall clusters, and orientation of extreme rainfall areas in the upper northeastern region of Thailand during the summer season (March to May) from 2017 to 2020. Rainfall data were obtained from Sakon Nakhon weather radar station. Radar reflectivity was converted to hourly rainfall amount using Z-R relationship for northeastern Thailand.    It was found that the spatially variable bias correction method, using rainfall observations at five ground stations, produces more accurate results compared to the mean field method (RMSE = 2.20 mm/hour). The results showed that all rainfall characteristics tended to increase from March to May. During the pre-monsoon period, especially in March, daily rainfall amount in the study area was quite low (1.59 – 4.14 mm/day). Heavy and extreme rainfall occurred in a few small-size clusters. In April, average rainfall amount and maximum rainfall became higher than other periods (718.13 – 800.82 mm). Moreover, proportion of heavy and extreme rainfall areas increased from March and showed relatively large variability over 4 years (SD of average daily rainfall = 5.16 mm/day). These findings indicated a likelihood of severe summer thunderstorms to occur in this period. In May, rainfall amounts and a number of extreme rainfall clusters increased (371.63 square kilometers per day on average) as a result of widespread rainfall over the study area due to southwest monsoon influences and low-pressure troughs (ITCZ). The second half of May exhibited the heaviest rainfall period with a large number of extreme rainfall clusters or a few clusters with extensive spatial coverage.

First Page

1

Last Page

24

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