1. A process for evaluating precipitation over an area of terrain, comprising the steps of: deploying automatic rain gauges within the area of terrain; synchronizing the rain gauges; providing, via the rain gauges, dated local rainfall data accumulated over a first chosen time interval sampling pixels of radar images over a plurality of reflectivity levels to obtain meteorological radar data with given radar periodicity, the radar images representing rain-bearing cells over a radar workspace which encompasses the area of terrain; analyzing a succession of radar images within the area of terrain to track main rain-bearing cells dynamically by their shape and motion; compiling a radar rainfall measurement chart by accumulating, for each pixel of the area of terrain, precipitations during a second chosen time interval which are due to the main rain-bearing cells by interpolating the shapes and positions of the main rain-bearing cells during the second time interval, selecting from the deployed automatic rain gauges at least one sub-array of at least four rain gauges which are separated from one another by about 2 to 4 kilometers and are affected by at least one main rain-bearing cell: and correcting a rainfall measurement chart as a function of a relationship between the rainfall data provided by the rain gauges of the selected at least one sub-array and rainfall data from the rainfall measurement chart taking into account a ratio between the first and second chosen time intervals