A systematic review on rainfall patterns of Thailand: Insights into variability and its relationship with ENSO and IOD

Abstract

Agriculture, a historically crucial sector for Thailand's economy, has been severely impacted in recent years due to global climate change causing widespread alterations in rainfall patterns across the country. Therefore, for developing resilient climate adaptation measures, it is important to understand the inter-annual variability of rainfall and its associated processes. Large-scale oceanic phenomena, such as El Niño Southern Oscillation (ENSO) and Indian Ocean Dipole (IOD), have played significant roles in controlling the inter-annual variability of rainfall across the Asian continent. In this study, we present a review of past studies with an emphasis on rainfall variability and its association with large-scale oceanic phenomena, such as ENSO and IOD, in Thailand. This study found that trends in annual and seasonal rainfall characteristics were heterogeneous, with both increasing and decreasing trends observed within the country and at the regional scale. Generally, ENSO significantly affects the rainfall variability across Thailand. Above-normal and below-normal rainfall are associated with the La Niña and El Niño years, respectively, in Thailand. However, the magnitude of ENSO's effects on rainfall variability in Thailand varies at both spatial and temporal scales. The review also shows a significant association between major IOD events and the Pacific Decadal Oscillation. The effect of IOD on rainfall variability was found to be weak to moderate across Thailand, although the effect was significant during the co-occurrence of IOD events with the ENSO events. Additionally, tropical depressions, tropical cyclones, and Inter-Tropical Convergence Zone's contribution are mainly associated with torrential rainfall and are an integral part of the interannual variability of rainfall across Thailand. In general, this review found that the contribution of different moisture sources, seasonal to intra-seasonal variations in rainfall, topographical variations, geographical location between Indian and Pacific oceans, and influence of large-scale variations including ENSO and IOD, make Thailand's rainfall highly complex at both spatial and temporal scales. Overall, the findings of this study would help scientists and policymakers understand the process and dynamics of rainfall variability and its association with large-scale oceanic phenomena in the study area.