Metrological requirements for a laboratory rainfall simulator

The liquid precipitation at the ground level is measured by means of different techniques and technologies for areal and point-scale quantification of rainfall intensity RI (mm/h) and the resulting total precipitation amount h (mm). Point-scale precipitation gauges fall in two main categories: catching type gauges, which collect the liquid equivalent precipitation into a measuring bucket, and non-catching type gauges, where the collection of water is not required. Since the latter category of gauges employ a variety of developing measuring technologies, the implementation of appropriate calibration procedures has been included within the scope of the European Metrology Research Programme MeteoMet 2 (ENV58-REG3). This work reports about a study conducted by the WMO-CIMO Lead Centre "B.Castelli" on Precipitation Intensity (LC-PrIn) aimed at the design and preliminary testing of an advanced laboratory rainfall simulator capable of generating non-continuous water flows (droplets) with controlled RI and the drop size distribution. A real-world drops size distribution is approximated by simplifying the domain of droplets diameter d (mm) in three main categories of fixed size. The technical advantage derived from the availability of such device arises from its suitability to calibrate non-catching type gauges.