Rivers at record lows, thunderstorms overhead: reading the September 2026 water data as a flood risk signal

England has just recorded one of its driest summers in decades, almost three-quarters of the country is officially in drought, and river gauges are logging record lows. It would be easy to conclude that flood risk is the one thing operations teams don't need to worry about this autumn. The data says otherwise — and this week's thunderstorm warnings are making the point in real time.

This is our regular look at what the official numbers are actually saying. All figures below come from the Environment Agency's monthly water situation reporting, SEPA's weekly water scarcity reports, and Met Office warnings in force this week.

What the August data shows: a country running on empty rivers

The Environment Agency's national water situation report for August 2026 makes stark reading. Every region of England received below-average rainfall for the month. Monthly mean river flows fell at around three-quarters of indicator sites, every indicator site was classed as normal or lower for the time of year, and more than half were classed as notably or exceptionally low.

The regional summaries fill in the detail. South-east England recorded just 55% of its long-term average rainfall for August, and two chalk-fed gauges — the River Coln at Bibury and the Thames at Farmoor — recorded their third-lowest August flows on record, the lowest since the 2022 drought. North-west England, normally the wet corner of the country, managed 84% of its average. East Anglia ranged from 44% to 106% of average depending on catchment, with monthly mean flows predominantly below normal or exceptionally low.

Soils tell the same story. The Environment Agency notes that soil moisture deficits reduced modestly after a wet end to August — but every region still has soils much drier than average for the time of year. That detail matters more for flood risk than any other number in the report, and we'll come back to it.

The drought picture: third time in five years

By late summer, 71.3% of England was officially in drought — the third declared drought in five years, after 2022 and 2025. Reporting on the National Drought Group's latest assessment notes that ten water companies have imposed hosepipe bans covering some or all of their customers, including Wessex Water's first ban in 50 years (from 18 August) and Bristol Water from 27 August. The same assessment warns the drought is likely to persist: Devon, Cornwall and East Anglia are projected to remain in active drought through April 2027, and the Met Office expects the second half of September to turn drier again in the south, where rain is needed most.

Scotland is running the same deficit on its east coast. SEPA's latest weekly water scarcity report holds North Fife, Fife (East Neuk), Stonehaven and the North Esk at Significant Scarcity — its highest category — with the Tay Estuary (North), Whiteadder Water, Berwickshire Coastal and the Lower Dee and Water of Feugh areas approaching the same level. River flows across much of eastern Scotland remain low to very low, and SEPA is explicit that recent rain produced only temporary recovery: the underlying deficit built over months has not been reversed.

Why low rivers do not mean low flood risk

Here is the counter-intuitive part, and the reason this report is worth a flood-monitoring team's attention rather than just a water company's.

Dry ground sheds water. Months of drought leave soils hard, compacted and in places water-repellent. When intense rain lands on them, it runs off rather than soaking in — behaving more like rain on concrete than rain on a field. We covered the mechanism in detail in Drought Then Deluge; the short version is that the flash flood risk from a summer downpour is often highest precisely when the landscape looks parched. Alastair Chisholm, water lead at the consultancy Arup, has warned that this drought will significantly elevate flash flood risk through the autumn and winter as heavy rain lands on baked catchments.

Surface water flooding doesn't read the river gauges. Insurance analysis by LexisNexis found that more than 90% of summer flood claims involve surface water, against roughly 55% in winter — because summer ground absorbs sudden downpours far less effectively than saturated winter soil. A river at an exceptionally low level tells you very little about whether a car park, loading bay or basement plant room will flood in a cloudburst. That blind spot is one we've examined before in Surface Water Flooding: the blind spot in portfolio flood risk.

Warmer air carries more water. The Met Office points out that each 1°C of warming lets the air hold about 7% more moisture — so when the pattern does break, the downpours that end a drought tend to be heavier than the ones that preceded it.

This week has supplied the live demonstration. The Met Office issued yellow warnings for thunderstorms across parts of England and Wales as warm, humid air gave way to heavy showers and longer spells of rain, with slow-moving, thundery downpours spreading north on Thursday, hail possible, and — in the Met Office's own words — the potential for localised flooding where significant rain falls in a short period. That rain is landing on the driest soils England has carried into an autumn since 2022.

What the 2022 precedent suggests about the months ahead

The 2026 drought keeps being compared to 2022, and the comparison is instructive for flood planning. The gauges recording their lowest flows "since 2022" are pointing at a year in which a record-dry summer gave way to an autumn and winter punctuated by intense rainfall and localised flooding, long before groundwater had recovered. Drought and flood are not opposite ends of a dial that the country moves along slowly; they are two states the system can occupy in the same season. The National Drought Group's projection that parts of England stay in drought into 2027 and the elevated autumn flash flood warnings are not contradictory statements — they are the same statement about a landscape that has lost its buffering capacity.

For operations and estates teams, three practical readings follow:

1. Re-weight surface water in your risk picture. For as long as soils stay abnormally dry, short-duration rainfall intensity matters more than river levels. Sites that sailed through wet winters can flood in a 40-minute cell. If your monitoring is built solely around river gauges near your sites, this is the season it will mislead you.

2. Treat rainfall warnings as operational triggers, not weather news. A yellow thunderstorm warning over a portfolio with drought-hardened ground deserves the same pre-agreed response — drain and gully checks, moving stock off floor level in vulnerable buildings, confirming pump readiness — that a flood alert would normally trigger. Our flood incident playbook sets out a 24-hour action structure that maps directly onto short-notice convective warnings.

3. Watch the recovery, not just the event. The autumn's defining question is how fast catchments rewet. Falling soil moisture deficits will progressively shift risk from flash surface water flooding back towards conventional fluvial flooding — and if the rewetting happens through a sequence of Atlantic storms, both can arrive together. The EA's monthly water situation reports, SEPA's weekly scarcity updates and Natural Resources Wales' equivalents are the documents to track; between them they describe the initial conditions every autumn storm will land on.

Monitoring through the transition

FloodWatch aggregates the official warnings and live river, rainfall and tidal data from the Environment Agency, Natural Resources Wales and SEPA into a single portfolio dashboard, refreshed on a 5-minute cycle. In a season like this one, that matters for a specific reason: the risk picture is changing week to week, and the signal is spread across three agencies' feeds and two very different flood mechanisms. A portfolio view — which sites sit under a live warning, what the nearest gauges are doing, what has changed since yesterday — is how a small operations team keeps pace with a transition season without someone manually triangulating government websites every morning.

The drought will end. On the evidence of 2022, it may end loudly. The teams that come through a drought-to-deluge autumn cleanly are the ones that treated the dry months as preparation time, not as a reprieve. See how FloodWatch supports portfolio flood monitoring across England, Wales and Scotland.