Abstract: Automatic rain gauges (P00-P0n) are employed within the area of terrain (ZT). A meteorological radar (R1) provides, with a given radar periodicity, a radar image representing rain-bearing cells of concern to the area of terrain. By analyzing the succession of radar images, the main rain-bearing cells are tracked dynamically by their shape and motion. Then a radar rainfall measurement chart is compiled by accumulating, in each pixel of the area of terrain, the precipitations due, during a second chosen time interval, to these main rain-bearing cells, with interpolation of their shapes and positions. At least one sub-array (PA, PB) of four rain gauges separated from one another by about 2 to 4 kilometers and affected by at least one main rain-bearing cell is selected. Finally, the rainfall measurement chart is corrected at least partially as a function of the relation between the accumulated true rainfall data and those from the said chart at the locations of the rain gauges of the sub-array.