<p>Drought is a major climatic hazard affecting regional water resources security. Based on monthly precipitation and potential evapotranspiration (PET) data at a 0.1° × 0.1° resolution from 1953 to 2022, this study calculated SPI and SPEI at 1, 3, 6, and 12 month time scales. Drought event identification, variance decomposition of climatic water balance, Theil Sen trend analysis, FDR significance correction, and variable fixed scenarios were used to examine the spatiotemporal variations in meteorological drought and the relative influences of precipitation and PET changes in the Lancang River Basin. The results showed that the number of drought events decreased markedly with increasing accumulation time scale. SPI and SPEI produced generally consistent drought identification results, while SPEI was more sensitive at some short time scales. The variability of climatic water balance was mainly controlled by precipitation variance, followed by the covariance term, whereas the PET variance term was relatively small. Trend analysis indicated significant increases after FDR correction in upstream SPI across all time scales. Upstream SPEI also showed positive slopes, but significant areas were limited. The midstream region showed negative slope tendencies at medium and long time scales, while downstream changes were weak and spatially heterogeneous. Seasonally, the wet season showed increases upstream and decreases in the midstream and downstream regions, whereas significant dry season increases were mainly concentrated in upstream SPI₆. Scenario analysis suggested that PET changes were more evident at short time scales and in local areas, while precipitation changes were more influential at medium and long time scales, especially upstream.</p>