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New monthly Hydrological summary published, for May 2011 – Remarkable contrasts across the UK
10 June 2011
Remarkable rainfall patterns across the UK in May produced a decrease in the spatial extent of drought conditions in England and Wales but an increase in their intensity in the most severely impacted regions.
Late May soils were the driest on record across large parts of eastern and central England – causing substantial agricultural stress (impacting on crop yields) and an increased risk of forest and heathland fires. Currently, the most evident hydrological impact of the drought is on river flows across much of southern Britain – flows in responsive rivers were close to, or below, previous late-May minima over wide areas.
The above analysis is contained within the latest monthly hydrological summary for the UK (for May 2011) produced by the National Hydrological Monitoring Programme, operated by the Centre for Ecology & Hydrology in conjunction with the British Geological Survey.
Most reservoir stocks throughout northern Scotland and Northern Ireland are healthy and, for England & Wales as whole, stocks were within 4% of the early June average. Despite the rainfall deficiency, stocks remain within about 10% of capacity in a number of major pumped-storage impoundments in the English Lowlands (e.g. the London Group and Farmoor). Elsewhere, many gravity-fed reservoir stocks have fallen to, typically, 10-20% below the early summer average with the greatest deficiencies in the South West, Wales and the Midlands.
Terry Marsh from the Centre for Ecology & Hydrology said, “The very moderate infiltration since the winter has left groundwater levels below, to well below, average across most major aquifers. Above average summer rainfall would ameliorate the drought’s impact but with soils still exceptionally dry in much of southern Britain drought stress will continue with an expected substantial delay in seasonal recovery in runoff and recharge rates and, correspondingly, notably low autumn flows.”
The 1975-76 drought was considered at the time the most severe yet experienced across much of the UK. Earlier this year CEH published a new, 58-page report providing a contemporary and retrospective review of the events of 1975 and 1976. The report, co-authored by hydrologists Terry Marsh and John Rodda is available to download here.
The Centre for Ecology & Hydrology jointly operates the National Hydrological Monitoring Programme (NHMP) in conjunction with the British Geological Survey. NHMP scientists produce the UK Monthly Hydrological Summary which assesses rainfall, river flows, groundwater and reservoir levels. They also operate the National River Flow archive. The NHMP has a remit to analyse major flood and drought events in the UK and analyse long term trends in UK hydrological data. The Programme was set up in 1988 and relies on the active co-operation of measuring authorities throughout the UK.
- A substantial proportion of eastern England registered <20% of the average May rainfall with totals falling to 4mm in parts of Kent – a dramatic contrast to north-west Scotland where some localities reported totals two orders of magnitude greater.
- Across much of the English Lowlands, the May rainfall was generally greater than that for March and April combined but, nonetheless, spring rainfall totals were only around 50% of the England & Wales average.
- England eclipsed its previous lowest spring rainfall total, reflecting extreme deficiencies in some eastern areas.
- The Anglian region registered its lowest 3-month rainfall total (for any start month) in a series from 1910 and, remarkably, the spring rainfall for Cambridge represented only around half of the previous minimum in a record from 1848.
- For England & Wales estimated runoff through the spring (March-May) of 2011 was only around 50% of average; only in 1976 has a lower spring runoff been recorded.
- In a significant proportion of England, end-of-May soil moisture deficits exceeded the previous highest on record. Correspondingly, there was minimal recharge to almost all aquifer outcrop areas and groundwater level recessions continued.
Read the full May 2011 Hydrological Summary for the UK [PDF, mb]
Details of the National Hydrological Monitoring Programme
Media enquiries related to the Hydrological Summaries should be directed to the CEH Press Office. Our scientists can provide explanation and analysis of historic hydrological patterns, possible future scenarios under climate change and scientific understanding of the current situation. We are not able to comment on immediate operational issues.
If you wish to reproduce figures from the Monthly Hydrological Summary please respect the copyright credits contained within the document.