Unraveling the variability of winter persistent dry spells in the levant via the Indian Ocean dipole

Abstract

Persistent dry spells (PDS) during winter in the Levant are a major hydroclimatic hazard, with significant impacts on water resources, agriculture, and regional socio-economic stability. Despite their importance, their sub-seasonal predictability remains limited. Here, we examine the statistical relationships between Indian Ocean sea surface temperature anomalies, focusing on the Indian Ocean Dipole (IOD), and winter PDS over the Levant.We find a robust association between positive IOD phases and large-scale circulation anomalies across the North Atlantic–Eurasian sector. These include geopotential height anomalies over eastern Europe and western Russia, enhanced cyclonic activity in the western Mediterranean, and increased Rossby wave activity, collectively favoring downstream blocking patterns conducive to persistent dry conditions over the Levant.PDS events are characterized by three dominant synoptic regimes, ‘Baroclinic,’ ‘Subtropical,’ and ‘Polar’. Their employment reveals different large scale response to IOD phase with the Baroclinic regime being the most prevalent and the most consistent with positive IOD-related circulation anomalies. Statistical analysis further shows that positive IOD conditions in December are associated with a higher frequency of prolonged dry spells (>15 days). Case studies from January 1998 and 2014 support these findings.Peter and Clark's Momentary Conditional Independence (PCMCI), a causal discovery framework for multivariate time series, implies that the weak direct IOD–PDS link is reconciled through a robust pathway involving 500 hPa geopotential height anomalies. Further process-based and modeling studies are needed to resolve the mechanism.Overall, the results suggest that tropical variability modulates mid-latitude circulation regimes relevant to PDS, highlighting the need to incorporate such interactions into sub-seasonal prediction frameworks. Plain language summary: Winter dry spells in the Levant can last for weeks and have serious impacts on water supply, agriculture, and daily life. However, predicting when these prolonged dry periods will occur is still challenging. In this study, we explore whether conditions in the tropical Indian Ocean, specifically a climate pattern known as the Indian Ocean Dipole (IOD), are linked to these dry spells in the Levant.We find that when the IOD is in its positive phase, it is often associated with large-scale atmospheric changes stretching from the Atlantic to Eurasia. These changes can alter the path of weather systems and promote stable high-pressure conditions over the eastern Mediterranean, which suppress rainfall and lead to persistent dry spells.Dry events tend to occur under a few typical weather patterns. The employment of these patterns indicates that each regime responds differently to the IOD and therefore diverse changes occur. The most prevalent regime demonstrates high consistency with positive IOD-related circulation anomalies. In particular, positive IOD conditions in December are associated with a higher chance of especially long dry spells later in winter.An advanced statistical method implies that the influence of the IOD is mostly indirect: it affects atmospheric circulation patterns, which in turn control dry conditions over the region. These results highlight how conditions in the distant ocean may influence regional weather and point toward ways to improve sub-seasonal forecasts, helping the region better manage water resources and adapt to climate variability.