September was generally a cool but sunny month with limited rainfall over the first three weeks. Thereafter cyclonic conditions prevailed with exceptionally high seven to ten-day rainfall totals. River flows climbed rapidly in the fourth week and floodplain inundations were very widespread from the 23rd; in many rivers flows remained close to, or above, bankfull for a week or more.
Provisional data suggest that September river outflows from England and Wales were the second highest since 1968 and the associated extensive flooding provided a dramatic climax to the wettest summer half-year (April-September) on record for the UK.
The above analysis is contained within the latest monthly hydrological summary (for September 2012) produced by the National Hydrological Monitoring Programme, operated by the NERC Centre for Ecology & Hydrology (CEH) in conjunction with the NERC British Geological Survey.
The exceptional runoff reversed a belated seasonal decline in reservoir stocks and early October stocks for England & Wales exceeded the previous monthly maximum (the fourth successive month in which this has occurred). Stocks in the great majority of index reservoirs are currently within 10% of capacity – remarkable for the early autumn.
Groundwater resources present a less coherent picture – due to a combination of rainfall patterns, soil moisture conditions and, more particularly, aquifer storage characteristics which determine the lag between surface infiltration and water-table response.
Terry Marsh, from CEH, said, “Groundwater levels in the generality of index wells are above, to well above, the early autumn mean but remain depressed in some of the slower-responding aquifers. However, the water resources outlook is far healthier than could have been envisaged during the early spring of 2012.”
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.
Read the full September 2012 Hydrological Summary for the UK [PDF, 1.72mb]
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.
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