Connections of ENSO/IOD and aerosols with Thai rainfall anomalies and associated implications for local rainfall forecasts

Abstract

El Nino/La Nina Southern Oscillation (ENSO), Indian Ocean Dipole (IOD) and aerosols have important roles to play in relation to Southeast Asian rainfall anomalies. This study investigates connections between these factors and local seasonal rainfall anomalies at 17 locations throughout Thailand using ground measurements and satellite observations available from 1980 to October 2011. This research investigates further the usefulness of incorporating these factors into rainfall forecasts. Results from canonical correlation analysis indicate that strong ENSO signals from October to March may affect rainfall anomalies in the nonsummer monsoon months, whereas IOD signals in the previous summer monsoon months were deemed to be of greater responsibility for current summer monsoon rainfall. Comparison of rainfall levels with different aerosol loadings suggests rainfall-decreasing aerosol from December to February for the South East Coast and in pre-summer monsoon months for deeper inland areas having less coastal influences. Rainfall-increasing aerosol was observed in post-summer monsoon months at the inland stations. The use of ENSO/IOD signals as predictors yielded better rainfall forecast model performance than that of the aerosol loading. However, model performance significantly improved when both ENSO/IOD signals and seasonal aerosol loadings were introduced.