September was an autumnal mix of fine warm weather, some crisp frosty mornings, sunshine and showers, and an intense stormy interlude. Rainfall was near average for the UK, but this disguised stark regional variations. Intense storms and persistent unsettled weather brought above average rainfall to large parts of the north and west, but areas further south and east received relatively meagre rainfall in September. Correspondingly, soil moisture deficits (SMDs) decreased across most of the UK (they increased in the south-east) and soils mostly remained drier than average for the time of year. River flows were below average in central, southern and eastern England and above average in parts of the north and west. In catchments draining the Highlands of Scotland, river flows ranged from exceptionally high in the west to exceptionally low in the east, reflecting the influence of storms from the west in September and longer‑term rainfall deficiencies, respectively. Groundwater levels continued to fall following their usual seasonal recession, but generally remained in the normal range for the time of year apart from the Chalk of south-east England where many levels were below average. Despite substantial increases in reservoir stocks in Scotland and Wales, storage remained more than 10% below average in Wales and a number of impoundments across the English Lowlands (where stocks decreased notably in September). With many reservoir stocks in the south and east remaining markedly below average for the time of year and groundwater recharge yet to commence across the major aquifers, the onset of replenishment will be influential in the outlook for water resources in 2019.
The full Hydrological Summary can be found here.