Odds Prediction of Drought Category Using Loglinear Models Based on SPI in the Northeast of Thailand

Wisoot Salee, Veeranun Pongsapukdee


The prediction of drought category is performed through Loglinear modeling for three dimensional contingency tables. The frequencies of drought categories are evaluated from a 12-month time scale by means of Standardized Precipitation Index (SPI), using the raw data obtained from 19 rain gauge stations in 19 provinces in the Northeast of Thailand. SPI monthly values were computed in a 12 month time scale for the period from January 1962 to December 2009, within 48 years or 576 months in each of 19 rainfall stations. The results show that the selected quasi-association loglinear model is an adequate model and appropriate tool to fit the data from 19 stations (P-value = 0.927). The values of various drought class transitions are estimated in three consecutive months. The predicted odds ratios and the corresponding confidence intervals are evaluated to predict the drought classes’ transitions. Even if, most of the results display for more normal drought classes than those of moderate or severity drought classes; however, there are still some areas of investigation that drought could be developed. Therefore, future monitoring of drought watch system is needed to be set the pace in these areas to keep up with them. Furthermore, an appropriate statistical model to predict drought phenomenon in each area is necessary and is probably able to provide more effectiveness in the administrative management of hazard from drought.

Key Words: Odds ratio; Drought class transitions; Three-dimensional loglinear models

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