Combining Rain Gauge and Radar Measurements of a Heavy Precipitation Event over Switzerland

The two main precipitation monitoring systems, rain gauge and radar measurements, exhibit complementary strengths and weaknesses. While rain gauges are fairly accurate in absolute values but suffer from a rather poor temporal and spatial resolution, radar offers a high temporal and spatial resolution but its values are often biased, particularly in mountainous terrain such as Switzerland. The aim of this study is to combine the two measurement platforms in order to incorporate their strengths and compensate their weaknesses in the resulting precipitation fields. The combination is performed by two different geostatistical methods: Kriging with external drift using radar measurements as trend variable and Ordinary Kriging of radar errors, yielding a field of radar errors, which is added to the radar field. As this is a first application of such methods for the area of Switzerland, it is performed as a case study. Five days of the heavy precipitation event of August 2005 are examined, containing predominantly convective as well as predominantly stratiform and orographic precipitation situations