PMEL Publications Abstract
FY 2027
Drought intensification in the intermountain west during second-dip La Niña events: Evidence from Utah
Chikamoto, Y., N.A. Hasan, W. Zhang, J.D.D. Meyer, R.R. Gillies, J. Stuivenvolt-Allen, and M.J. McPhaden
J. Appl. Meteorol. Climatol., 65(10), 1633–1653, doi: 10.1175/JAMC-D-26-0033.1, View article at AMS (external link) (2026)
Reliable seasonal drought forecasts are critical for water management in the Intermountain West, yet hydroclimate predictability in this region remains limited because canonical El Niño–Southern Oscillation (ENSO) teleconnections are weak and spatially inconsistent. Here, we show that Utah experiences a robust and coherent drought response during the second dip of multiyear La Niña events, in contrast to the weak and variable responses observed during preceding El Niño and first-dip La Niña winters. Composite analyses of gridded reanalysis products, statewide climate indices, and station-based observations reveal that second-dip La Niña events are characterized by reduced winter–spring precipitation, anomalously warm temperatures, and increased numbers of dry and warm days. These conditions result in diminished 1 April snow water equivalent, suppressed summer streamflow, reduced soil moisture, and strongly negative Palmer Drought Severity Index anomalies across Utah. By contrasting early (1951–90) and recent (1991–2023) periods, we further show that these drought responses have intensified under a warming climate. While the large-scale circulation anomalies associated with second-dip La Niña events primarily reflect internal ENSO-related variability, rising temperatures amplify drought severity through increased evaporative demand, reduced runoff efficiency, and earlier snowmelt timing. Together, these results indicate that second-dip La Niña winters provide an enhanced and physically grounded source of seasonal drought predictability for Utah. Incorporating second-dip La Niña signals into drought early warning systems may therefore improve water resource planning in snow-dominated, topographically complex regions of the Intermountain West.
Significance Statement. Reliable seasonal drought prediction remains a major challenge in the Intermountain West, where water resources support agriculture, ecosystems, and rapidly growing populations. In Utah, hydroclimate responses to traditional climate drivers such as El Niño and single-year La Niña events are often weak or inconsistent, limiting the usefulness of conventional seasonal forecasts. This study shows that drought risk increases markedly when La Niña persists for two consecutive winters. These second-dip La Niña events are associated with consistently warmer and drier winter–spring conditions, reduced snowpack, and suppressed summer streamflow, culminating in intensified statewide drought. Although the large-scale circulation anomalies primarily reflect internal ENSO-related variability, background warming amplifies drought severity by increasing evaporative demand and reducing runoff efficiency. Identifying second-dip La Niña events therefore provides a physically grounded and actionable pathway for improving multiseason drought early warning and supporting proactive water management in snow-dominated regions of the Intermountain West.