Assessment of meteorological drought in Thailand: Historical and future projections under CMIP6 climate change scenarios

Study region Thailand. Study focus This study assesses historical and future meteorological drought hazard across Thailand using the NASA NEX-GDDP-CMIP6 dataset. Thirty-five Global Climate Models (GCMs) were evaluated against observations using the modified Kling–Gupta Efficiency (KGE′), and 19 models were retained. The selected models with relatively high performance were bias-corrected using Empirical Quantile Mapping (EQM) for the baseline period and Equiratio CDF Matching (EQCDF) for future projections. They were then used to calculate the Standardized Precipitation Index (SPI) and Standardized Precipitation Evapotranspiration Index (SPEI). Drought event, duration, severity, and intensity were then combined into a composite Drought Hazard Index (DHI) to evaluate drought hazard under the baseline period and future SSP2–4.5 and SSP5–8.5 scenarios. New hydrological insights for the region The selected GCMs reproduced historical climate conditions reasonably well after bias correction, providing a reliable basis for drought projection. SPI and SPEI showed broadly similar historical drought patterns. However, their future projections diverged, particularly at longer timescales. Future SPEI projections generally indicate more severe and prolonged drought conditions compared to SPI, reflecting the increasing influence of atmospheric evaporative demand represented through potential evapotranspiration (PET) in SPEI. This divergence becomes more pronounced with increasing accumulation periods, suggesting the growing importance of cumulative evaporative-demand-related processes in long-term drought assessment. Regional analyses reveal substantial spatial heterogeneity, with certain areas exhibiting stronger sensitivity to temperature effects. Compared with SPI, SPEI indicated stronger evaporative-demand-driven shifts in drought hazard under future scenarios, particularly under SSP5–8.5. Regional analyses showed that northeastern Thailand is likely to remain the most drought-prone region, with consistently high variability in drought hazard. The central and eastern regions showed greater uncertainty and stronger future shifts, whereas the southern region remained relatively less vulnerable with more stable mean hazard levels. These results suggest that precipitation-only indices may underestimate future drought risk in a warming climate and highlight the need to incorporate temperature-sensitive drought indices into national drought monitoring, regional adaptation planning, and water resources management in Thailand.