The WMO Field Intercomparison of Rainfall Intensity Gauges was carried out in Vigna di Valle, Italy from October 2007 to April 2009, at the kind invitation of the Italian Meteorological Service. This intercomparison is following up on the Laboratory Intercomparison of Rainfall Intensity Gauges. CIMOXIV recommended that welldefined and accepted reference instruments and procedures were needed for the field intercomparison. CIMOXIV agreed that such reference might be based on a set of high quality devices applying different measuring techniques and had adopted a recommendation to that effect. The main objective of this intercomparison was to intercompare the performance of in situ rainfall intensity instruments of different measuring principles in high rainfall intensity conditions. An International Organizing Committee was set up to determine and agree on the rules of the intercomparison and to support its preparation and execution. The IOC was also tasked to agree on the procedures used for the evaluation of the results and to review and agree on their presentation in the final report of the intercomparison. This report presents in a detailed manner the procedure that was adopted to determine the reference rainfall intensity, based on the measurements of 3 instruments placed in a pit. It also contains datasheets for each of the participating instruments, which provide exhaustive information on their performances throughout the intercomparison period in the field, as well as under laboratory conditions. The final conclusions of the report highlight the challenges that this type of measurements represents due to the high variability of rainfall intensity at a 1minute time scale. A number of recommendations were drawn from the results and address topics such as how to make best use of existing instruments, how to improve the design and documentation of the instruments as well as matters like the standardization of rainfall intensity measurements. Consequently, they are relevant to users, manufacturers and the meteorological community as a whole.
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