The Environment Agency provisional Water Situation report for May shows encouraging news for the Southeast region after the prolonged dry period

Summary – May 2012

Despite some heavy rainfall at the beginning of the month, the total monthly rainfall for May was below the long term average. Groundwater levels are rising and responding to the very high rainfall in April and continued heavy showers at the beginning of May. River flows have also responded to the rainfall and then fallen back down during the drier weather of the last 11 days.

Rainfall

A total of 80% of the long term average rainfall for May was recorded this month. This was the 12th month in the last 20 months of below average rainfall. Heavy showers and lighter more persistent rain fell over the first two weeks. The highest daily total of 29.2mm was recorded at Plumpton College (River Ouse catchment) on the 9th . This wet weather was followed by 11 days of virtually no rainfall at the end of the month. With such wet weather in April and the beginning of this month, the summer so far (April and May) has been the 2nd wettest on record for the Wey Greensand, Chichester Chalk and Arun areal units. Solent and South Downs Area has been the 3rd wettest on record. However, the last 20 months includes 2 dry winters with Cotswolds West, Berkshire Downs, Upper Thames and Cherwell areal units experiencing the 2nd driest 20 months starting in October on record.

Soil Moisture Deficit,

Recharge and Groundwater Levels Soil moisture deficits (SMDs) had been reduced to zero by the end of April, but with below average rainfall over the course of May, SMDs rose during the month to peak at almost the average for the time of year. With zero or very low SMDs at the beginning of the month coupled with the rainfall, some recharge to the groundwater occurred. In turn the groundwater levels have risen at most of the key groundwater sites, although some of these increases were just levelling off by the end of the month in response to the dry weather. 5 of the key sites remain exceptionally low (down from 10 sites last month), 3 sites are notably low, 1 site is below normal, 4 sites are now normal, 1 site is above normal and 2 sites have reached exceptionally high levels for May. Despite these increases many of the key sites remain at record lows for May.

Ashley Green remains the lowest May on record and Stonor, Well House Inn and Sweeps Lane are all at the 2nd lowest May level on their records. At Stonor and Sweeps Lane, only May 1992 has been drier and at Well House Inn the lowest May level was recorded in 1944.

River Flows

River flows were high at the start of the month and these higher flows continued into May in response to the rainfall recorded in the first two weeks of the month. Flows fell during the second half of the month, but the monthly average flows have remained quite high. Flows at Eynsham on the River Thames were the 2 nd highest on record for the end of May. Only May 1983 has been higher. Flows on the River Arun at Alfoldean and River Rother (Western) at Iping Mill were the 4 th highest on record for May. In total 23 Flood Alerts and 2 Flood Warnings were issued during May in the South East Region, split between the 1st and the 9th /10th of the month. A majority of the surface water sites have flows at normal or above. Only 3 sites are below normal, 5 sites are normal, 5 sites are above normal, 7 sites are notably high and 1 site is exceptionally high. 6 sites were below normal or lower last month.

Reservoir Storage/Water Resource Zone Stocks

Reservoir storage is close to or at 100% for the Lower Thames, Lee Valley, Farmoor, Bough Beech, Arlington and Powdermill reservoirs. Storage fell at Farmoor in the middle of the month due to water quality problems, but this was quickly resolved and storage brought back up to almost 100%. Storage has risen at Ardingly, Bewl, Darwell and Weir Wood reservoirs over the month, and only Bewl remains just below the long term average for May.

The full report can be found here