The influence of El Niño-Southern Oscillation on cool-season precipitation variability in the arid Middle East

Abstract. Interannual variability in precipitation across the Middle East is of high societal and environmental relevance given the region's arid climate and limited water resources. While previous studies have linked the El Niño-Southern Oscillation (ENSO) to interannual precipitation variability in the Middle East, the understanding of this linkage and the underlying mechanisms remain fragmented. Using observation-based datasets and a range of diagnostics, this study quantifies the influence of ENSO on Middle Eastern precipitation variability during the extended cool season (October–May) and presents an integrated perspective on the driving atmospheric mechanisms. Consistent with previous studies, we find that El Niño is associated with increased precipitation, whereas La Niña is associated with decreased precipitation. This relationship is asymmetric and varies substantially within the cool season, with a strong precipitation increase during autumn and a modest increase in spring under El Niño conditions, and a persistent precipitation decrease throughout the cool season under La Niña conditions. These precipitation increases (decreases) during El Niño (La Niña) are associated with an equatorward (poleward) displacement of the subtropical jet and increased (decreased) Rossby wave breaking frequencies at the poleward flank and beneath the jet core. Simultaneously, a mid-tropospheric cyclonic (anticyclonic) circulation anomaly over the Middle East strengthens (weakens) atmospheric moisture transport into the region, contributing to enhanced (reduced) tropospheric moisture content and instability. From a global perspective, three different atmospheric mechanisms contribute to these regional circulation patterns: (1) a zonally symmetric shift in the meridional position of the subtropical jet along with anomalies in Rossby wave breaking frequency, (2) a barotropic Rossby wave response emanating from the tropical Pacific toward the Middle East via the extratropics, and (3) a baroclinic perturbation in the tropical circulation extending westwards over the Indian Ocean and South Asia consistent with a Gill-Matsuno-type response. Co-varying circulation patterns over the Indian Ocean, associated with the Indian Ocean Dipole, likely contribute to intraseasonal variability in ENSO's influence on Middle Eastern precipitation. Our findings advance process understanding of precipitation variability in the water-scarce Middle East, having implications for seasonal prediction, flood and drought warning, and the evaluation of climate projections.