Analysis of Rainy Days in Northeast Thailand

Abstract

              Approximately 7.8 percent of the agricultural area in Northeast Thailand is irrigated with the remaining area under rainfed agriculture. Attempts to analyze characteristics of rainy days were carried out in order to understand the estimated rainfall characteristics of the Northeast. Analysis was made by comparing numbers of rainy days within the rainy season, mapping regional spatial rainy days and interpreting the coefficient of variation of rainy days and of no-rain days both spatially and temporally. 

               Results of the analysis are summarized as follows: the periodical characteristic of rainy season could be divided into 4 periods: 1) a pre-rain period, from April 6 to May 3; 2) the first rainfall peak, from May 4 to July 10; 3) the second rainfall peak, from July 11 to October 7; 4) a post-rain period, from October 8 to October 17. It was identified that the large area of latitude approximately below 17° 12' 10" to the southern part of the region had rainy-day phenomena during the rainy season in accordance with the above characteristics of the first and the second rainfall peaks. Nakorn Phanom and Ubon Rachathani provinces had 100-110 rainy days. Intermediate numbers of rainy days were scattered all over the region. The zone of rainy day numbers lower than 60 rainy days occupies the west and some parts of the central also accompanied with high coefficients of variation. These parts of the region were in agreement with 135-150 no-rain days occuring during the rainy season which represented severe drought prone areas. In general, the coefficient of variation decreased with increasing the number of no-rain days, confirmed drought occuring in most parts of the northeast.