107 millimetres of rain, 1.8 points of reservoir

Storms that blow over Sussex make the news. A reservoir that drains slowly does not. This week the two met, and the storms lost.

At a modelled grid point near Haywards Heath, a few miles from Ardingly reservoir, only 21.7 mm of rain fell between 1 and 19 October⁴. Then the storms came, and by Tuesday 27 October the month’s total was 107.0 mm, against a 1991–2020 average of 62.4 mm for the same days⁴. Desk arithmetic: about 171 per cent of normal, and most of it fell in five days.

Now look at the reservoir. On Sunday 25 October South East Water put Ardingly at 18.8 per cent full², a rise of 1.8 points after Storms Austen and Boelo³. The rain did not go missing. The Environment Agency explains where it went: soils have to be saturated before rainfall can recharge resources, and soils across much of England are still drier than normal for the time of year¹. The ground gets paid first. The reservoir gets what is left.

That is why the Agency’s weekly report reads like a careful set of accounts, not a weather bulletin. As of 22 October, England had received 52 per cent of its average October rainfall, national reservoir storage stood at 54 per cent of capacity, about 22 per cent below normal for the time of year, and 13 reservoirs or groups were classed as exceptionally low, Ardingly among them¹. Parts of Cornwall, Devon, Dorset, Somerset, East Sussex and West Sussex have been in severe drought since 15 October¹. South East Water’s head of water resources, Nick Price, said the rain had “helped maintain river flows”, and he warned that forecasts point to drier days again³.

The useful thing about the dull machinery is that it is already running. Drought permits, temporary use bans and weekly reports keep turning whatever the weather does¹. If you live in the south of England, the details of any ban in your area are on your water company’s website¹. A wet week is welcome, but it does not end a drought.