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National Hydrological Monitoring Programme - Monthly Hydrological Summary for the UK

The National Hydrological Monitoring Programme (NHMP) produces the monthly Hydrological Summary of the UK. This regular report describes the hydrological conditions during the preceding month, using the data holdings of the National River Flow Archive and National Groundwater Level Archive. Focusing on rainfall, river flows, groundwater levels and reservoir stocks, it places the events of each month, and the conditions at the end of the month, in a historical context.

Latest month

Click below to access the Hydrological Summary for the latest month:
May 2015 [PDF, 5.3 MB]


Archived versions of the Hydrological Summary are available in pdf format from December 1988. To access hydrological summaries from the archive, select the year and month below:

Year:   Month:  

The National Hydrological Monitoring Programme (NHMP) was instigated in 1988 and is undertaken jointly by the Centre for Ecology & Hydrology (formerly the Institute of Hydrology, IH) and the British Geological Survey (BGS).


The National Hydrological Monitoring Programme (NHMP) uses a subset of the National River Flow Archive gauging stations, National Groundwater Level Archive index wells, and measuring authority and water company reservoirs for analysis within its monthly Hydrological Summaries.

Data sources

River flow and groundwater level data are provided by the Environment Agency, Natural Resources Wales, the Scottish Environment Protection Agency and, for Northern Ireland, the Rivers Agency and the Northern Ireland Environment Agency. In all cases the data are subject to revision following validation (flood and drought data in particular may be subject to significant revision).

Reservoir level information is provided by the Water Service Companies, the Environment Agency, Scottish Water and Northern Ireland Water.

The National River Flow Archive (maintained by Centre for Ecology & Hydrology) and the National Groundwater Level Archive (maintained by BGS) provide the historical perspective within which to examine contemporary hydrological conditions.


Most rainfall data are provided by the Met Office. To allow better spatial differentiation the rainfall data for Britain are presented for the regional divisions of the precursor organisations of the EA, NRW and SEPA. Following the discontinuation of the Met Office's CARP system in July 1998, the areal rainfall figures have been derived using several procedures, including initial estimates based on MORECS*. Recent figures have been produced by the Met Office, National Climate Information Centre (NCIC), using a technique similar to CARP.

A significant number of additional monthly raingauge totals are provided by the Environment Agency and SEPA to help derive the contemporary regional rainfalls. Revised monthly national and regional rainfall totals for the post-1960 period (together with revised 1961-90 averages) were made available by the Met Office in 2004; these have been adopted by the NHMP. As with all regional figures based on limited raingauge networks the monthly tables and accumulations (and the return periods associated with them) should be regarded as a guide only.

The monthly rainfall figures are provided by the Met Office (National Climate Information Centre) and are Crown Copyright and may not be passed on to, or published by, any unauthorised person or organisation.

*MORECS is the generic name for the Met Office services involving the routine calculation of evaporation and soil moisture throughout Great Britain.

The Met Office
FitzRoy Road
Tel.: 0870 900 0100
Fax: 0870 900 5050

The National Hydrological Monitoring Programme depends on the active cooperation of many data suppliers. This cooperation is gratefully acknowledged.

Some of the features displayed on the maps contained in the reports are based on the following data with permission of the controller of HMSO.

(i) Ordnance Survey data. Crown copyright and/or database right 2005. Licence no. 100017897.
(ii) Land and Property Services data. Crown copyright and database right, S&LA 145.
(iii) Met Office rainfall data. Crown copyright.
All rights reserved. Unauthorised reproduction infringes crown copyright and may lead to prosecution or civil proceedings.

Text and maps in this document are NERC (CEH) 2008 unless otherwise stated and may not be reproduced without permission.