THE RELATIONSHIP BETWEEN THE CLIMATIC INDICES AND THE RAINFALL FLUCTUATION IN THE LOWER CENTRAL PLAIN OF THAILAND

摘要

Global climate changes are revealing the interconnections between natural conditions, natural resources, and regional climate variability that may affect the rain fluctuation. Rainfall plays an important role in the process of hydrology. This research presents an analysis of rainfall in the lower central plain of Thailand and the climate variability/oceanographic events in the wider geographical region, including the El Nino/Southern Oscillation (ENSO), Asian Summer Monsoon (ASM), and Indian Ocean Dipole (IOD). Data from 1980-2010 and 2011-2014 were collected for calibration and verification. Next, the frequency domains, spectra, and wavelet transforms were analyzed, together with the climate index and rainfall. The results revealed that rainfall occurs in seasons, yearly cycles, and off-seasons. The behavior of ASMs, for example, Indian Summer Monsoon Index (IMI) and Western North Pacific Monsoon Index (WNPMI), is the most similar to that of rainfall events, while the similarity of the other indices to rainfall events is not so strong. Cross-correlation analysis showed that there were delays between the climate indices and rainfall, so that multiple linear regression with lag time is required for further analysis. The results illustrate that the cross-correlation coefficients of IMI and WNPMI with rainfall are both approximately 0.6. The multiple regression with lag time shows that the average multiple coefficient correlation (R) is 0.64.. The indicator of the summer monsoon index value is WNPMI, which is the most influential factor for rainfall. Finally, the proposed equations, based on the cross-correlation and multiple-linear regression with lag time techniques, can be used to predict precipitation and be applied to the development of rainfall forecasting in the future.