The NRFA provides the catchment daily rainfall (CDR) series to aid the interpretation of river flow data.
Definition
A time series of the total rainfall averaged over the catchment in millimetres for each day.
Access
Catchment daily rainfall data is available to download on the NRFA Daily Flow Data pages for each gauging station (e.g. 39001 - Thames at Kingston). Catchment daily rainfall data is available from the start of the daily flow record.
Computation and accuracy
The catchment-averaged daily rainfall data have been derived from the Met Office HadUK-Grid Gridded Climate Observations on a 1km grid over the UK, version 1.3.0.ceda. The data have been interpolated from meteorological station data onto a uniform grid to provide complete and consistent coverage across the UK.
Information about the computation methods will be added shortly.
More information on the HadUK-Grid dataset can be found on the Met Office website.
The catchment boundaries used for calculating catchment average daily rainfall are those available for download from the NRFA Catchment Information pages for each gauging station. To calculate average rainfall over a catchment, a weighted zonal averaging method was applied that accounts for the spatial overlap between the grid cells and the catchment boundary. Each grid cell intersecting the catchment polygon was assigned a weight proportional to the fraction of its area contained within the catchment. The rainfall values were then combined as a weighted mean, ensuring that partially intersecting cells contributed appropriately to the average. The impact of this approach on total catchment average rainfall will be negligible for large catchments, but may be significant for smaller catchments, particularly in areas of high rainfall variability. The uncertainties within the underlying gridded rainfall are also larger in these areas, driven by the density of the rain gauge network
Read more about catchment area and boundaries.
Catchment monthly rainfall
The NRFA can also provide the catchment monthly rainfall (CMR) series, which is derived from the catchment daily rainfall series, on request.