Analysis of the Standardized Precipitation Index (SPI) and Its Relationship with El Niño-Southern Oscillation in the Potosí River Basin, Northeastern Mexico

This study characterizes meteorological drought in the Potosí River Basin, northeastern Mexico, using the Standardized Precipitation Index (SPI), evaluates its relationship with El Niño-Southern Oscillation (ENSO), and examines its relevance to the 2021–2023 Nuevo León water crisis. Daily precipitation from 13 stations (1995–2024) was homogenized using Climatol, and the 3-month SPI (SPI3) was related to the Oceanic Niño Index (ONI) through lagged correlation and phase comparisons accounting for temporal dependence. Of 1326 drought events identified, selected episodes were cross-corroborated against dendrochronological and tropical cyclone records. All 13 stations showed a positive SPI3-ONI association (r = 0.13–0.36), though only 4 retained significance under the primary, autocorrelation-adjusted criterion. Under conventional tests, SPI3 was lower during La Niña than during Neutral or El Niño at all 13 stations; these contrasts held at 10 and 9 stations under the Relative Oceanic Niño Index (RONI), and dependence-preserving bootstrap supported them at 12 and 10, while El Niño-Neutral was not robust. The network-average 12-month SPI (SPI-12) reached −1.11 in July 2022, and 26 of 30 months (August 2020 to January 2023) were La Niña. ENSO contributes a spatially widespread but modest component of drought variability, mainly through La Niña-related drying; the water crisis coincided with unfavorable climatic conditions but is not attributable to ENSO alone.