Hydrological Summary September 2023 Published

The first half of September was characterised by high pressure and temperatures, and the second half by autumnal wind and rain. Temperatures exceeded 30o C each day from 4th-10th (the longest run of consecutive days seen in September) contributing to the joint warmest September for the UK on record (equalling the previous maximum established in 2006, in a series of 140 years). Rainfall was above average, with intense but localised thunderstorms giving way to more widespread outbreaks of rain. Accordingly, many river flows were above average. Groundwater levels continued to recede at most sites, with levels mainly normal to above normal; a notable exception was the ongoing low levels in the Devonian sandstones of Scotland. Reservoir stocks at the national scale increased relative to average and remained healthy (at least 10% above average for Scotland, Northern Ireland and England). Stocks at Loch Thom saw recovery, but those at and Celyn & Brenig, Colliford, Roadford and Ardingly remained at least 10% below average. Water resources are healthy and the outlook for the next three months for most of the UK is for normal to above normal flows and groundwater levels (with the focus turning towards flood-risk in early October in Scotland). However, where impoundments have below average stocks, and in localised areas with below normal groundwater levels and river flows, continued vigilance will be required through the autumn months.

Read the Hydrological Summary