ECMWF SEAS5 Seasonal Precipitation Outlook and Hydrological-Hydrogeological Assessment for the Middle East: August 2026-January 2027

<jats:p>This preprint presents a regional hydrological and hydrogeological interpretation of the ECMWF SEAS5 System 51 ensemble-mean precipitation forecast initialized on 1 August 2026 for the Middle East and adjacent portions of the analysis domain. The supplied NetCDF field is time-mean total precipitation rate (tprate; m s^-1), converted to monthly precipitation depth (mm/month) using the actual number of days in each valid month. Six lead months were analysed, corresponding to August 2026 through January 2027, on the original 1-degree by 1-degree analytical grid. The derived products include monthly precipitation maps, six-month accumulation, October 2026-January 2027 accumulation, peak monthly precipitation, coefficient of variation, representative-city statistics, and three-dimensional visualizations. The strongest six-month accumulation in the grid is 1035.51 mm at 41.5 degrees N, 41.5 degrees E in the eastern Black Sea/northeastern Turkey sector, while the October-January maximum is 830.26 mm at the same grid cell. The largest single-month grid value, 434.62 mm/month at 12.5 degrees N, 37.5 degrees E, lies on the southern fringe of the rectangular domain in the Ethiopian Highlands and is therefore treated separately from the core Middle East interpretation. Among the sampled cities, Erbil has the largest six-month total (581.29 mm), followed by Beirut (510.55 mm) and Istanbul (433.34 mm), whereas Abu Dhabi has the smallest sampled total (38.96 mm). The forecast evolves from predominantly summer-dry conditions across much of the Middle East in August-September toward stronger autumn-winter precipitation across the Eastern Mediterranean, Anatolia, northern Iraq, the Zagros belt, and parts of western and northern Iran. Hydrologically, these patterns indicate where seasonal catchment wetting and runoff loading are greatest, but they do not resolve storm intensity, discharge, or inundation. Hydrogeologically, higher precipitation may enhance recharge opportunity in fractured, karstic, mountain-front, and alluvial aquifers, but precipitation cannot be equated directly with recharge because evapotranspiration, soil storage, runoff, lithology, depth to groundwater, and antecedent moisture control the partitioning of water. The results are therefore presented as an absolute seasonal precipitation outlook rather than an anomaly or flood-hazard forecast; hindcast-based climatology and skill assessment are required before statements of above-normal or below-normal precipitation are made.</jats:p>