Precipitation Measurement and Hydrology

Good agreement between radar and raingauges is found close to radar sites (13 % error for 6 hours of integration in a well defined catchment area) but strong variability and underestimation by radar occurs at longer ranges. The better of the two Swiss radars sees on the average only 25 % of the rain - in spite of the fact, that i t measures 100 % close to the radar (Sec. 4.6) - because of earth curvature or shielding by topography (See. 3.1). Similar, but not quite so dramatic results are found in flat country. In other words, the main problem of using radar för precipitation measurements and hydrology in operational applications comes from the inability to measure precipitation close enough to the ground. Because of the fact that this problem is hardly detectable in well defined experiments, i t did not reeeive the attention in the past which i t deserved as a dominant problem in operational applications at longer ranges.