The Hydrological Radar Experiment (HYREX) was a UK Natural Environment Research Council (NERC) Special Topic which ran from May 1993 to April 1997. The broad aim of HYREX was to gain a better understanding of rainfall variability, as sensed by weather radar, and how this variability impacts on river flow at the catchment scale.

Six projects were funded involving groups from CEH Wallingford (formerly the Institute of Hydrology), the Rutherford Appleton Laboratory and the universities of London (Imperial College and University College), Newcastle, Reading (including the Joint Centre for Mesoscale Meteorology or JCMM) and Salford. The projects ranged from research on improved precipitation measurement using polarisation and vertical pointing radars, through network design of radar/raingauge networks and spatial-temporal modelling of rainfall fields, to rainfall forecasting based on stochastic and meteorological concepts. An overview of the six HYREX projects and a list of the members of the HYREX Steering Committee are available as separate documents.

The experiment was centred on the Brue catchment in Southwest England. The common experimental infrastructure comprised two national network C-band radars at Wardon Hill (Doppler) and Cobbacombe Cross, a purpose-built dense raingauge network, an automatic weather station (AWS), an automatic soil water station (ASWS), and a river gauging station. These instruments have provided a continuous record throughout HYREX. Further instrumentation, deployed on an occasional basis, included an experimental S-band Doppler dual polarisation radar at Chilbolton and an associated line network of rapid-response raingauges (operated by Rutherford Appleton Laboratory), a transportable vertically pointing X- band radar (operated by the University of Salford), the UK Meteorological Office (UKMO) Research Flight and radiosonde network, and a disdrometer (operated by CEH Wallingford). The JCMM provided output from special runs of the UKMO Unified Model (UM). Infrastructure support was provided by the UKMO, the Environment Agency (EA), NERC, Rutherford Appleton Laboratory, the Ministry of Agriculture, Fisheries and Food (MAFF) and the water utilities.

The occasional deployment of some instruments was scheduled to coincide with a number of one or two day Intense Observing Periods (IOPs), triggered by meteorologically interesting conditions, during which radiosonde ascents and aircraft overflights were made, and for which special runs of the Unified Model were made.