Patterns of wet season rainfall in Northeast Thailand.

Spatial and temporal patterns of wet season (April-Octerber) rainfall in Northeast Thailand have been analyzed using thirty years of continuous daily rainfall data collected from forty stations located throughout the region Building upon the known, largely bimodal temporal of rainfall associated with the Southwest monsoon in this part of Southeast Asia the wet season is divided into four periods: the onset of rains two peak rainfall intensity periods and the termination. Summaries of daily rainfall data are analyzed in terms of rainfall effectiveness classes based on general crop growth needs. The frequency of occurrence of these are mapped along with a measure of their variability. A broad southwest-northwest pattern of increasing mean rainfall is observed in both peak intensity periods and there is generally a greater number of days with rain during the second rainfall peak. In the northernmost parts of the region, however, rains occur with virtually equal frequency in both the first and second peak periods. Variability in rainfall is greatest in southwestern section of Northeast Thailand and the analysis reveals four drought-prone areas which straddle several provinces (Changwat) in the west and central parts of the region. The results underline the utility of detailed analysis of medium-term daily rainfall data and the need for maintaining such records as part of the water resource for the Northeast.