Accuracy of rainfall estimates by two radars in the same Alpine environment using gage adjustment

A technique is analyzed to mitigate the hostile effects of a complex orogra phy on precipitation estimated by radar. Radar observations are adjusted us ing a network of gages. The corrections of radar estimates are derived thro ugh a Weighted Multiple Regression as a function of (1) the distance from t he radar, (2) the minimum height a meteorological target must reach to be v isible from the radar site, (3) the height of the ground at each pixel. Two C-band radars 140 km apart in an Alpine region are analyzed. About 60 rada r-gage data pairs are available for each radar in a 25,000 km(2) area durin g an extreme Mediterranean event (precipitation measured by the gages durin g the 40-hour observation period ranges from 36 to 444 mm). In the radar-ga ge comparison the data pairs are divided into two groups: one is used for t raining, the other for testing, and vice versa. All the radar-gage data pai rs are used for training, when comparing the two radars. Then radar-derived precipitation estimates are compared in a "mutual coverage" area (approxim ate to 10,000 km(2)). In all cases the correction significantly reduces the bias and the standard deviation of precipitation difference. In spite of t he different ages, technologies, and distances from the area of interest, b oth radars have shown similar behavior, and the proposed procedure can be s uccessfully applied to both.