Regional dependency of precipitation-altitude relationship in the Swiss Alps

The spatial distribution of the regional long-term rate of precipitation change, Delta P, with altitude in Switzerland is analysed. In order to eliminate the bias of point precipitation measurement, the analysis is based on precipitation sums corrected for the systematic error of precipitation measurement, particularly the wind-induced error and wetting losses. The Delta P values indicate a large spatial heterogeneity. They show different local and regional patterns. In this respect, the effect of the main alpine ridge dividing the Swiss territory into northern and southern parts is crucial. Water budget computations indicate that the regional Delta P values have a tendency to overestimate areal precipitation. The possible reasons are the redistribution of precipitation by wind and its accumulation in the valleys and, at the same time, the biased precipitation networks preferring location of gauges also in the valleys.