Dual-polarization radar observations of heavy rainfall in Finland

A heavy rainfall definition is somewhat ambiguous. It depends on local climatology, and intended use. In this work, we study applicability of dual-polarization radar QPE algorithms for urban hydrological applications. The Helsinki sewer system is build to handle rainfalls with a return period of 1 to 3 years. This return period translates into rain rates of 0.08 mm/min (48 mm/hour) for a duration of 15 minutes. Therefore, for urban hydrological applications rain rates exceeding or equal to 48 mm/hr can be considered as heavy. Accurate estimation of rain intensities that exceed or equal to this value is very important for hydrological applications.

Based on 5 years of DSD observations we have defined dual-polarization radar QPE algorithms. Using Helsinki Testbed measurements and Finnish Meteorological Institute operational rain gauge network we quantify the advantage of applying dual-polarization radar QPE algorithms over more traditional ones. This work is a part of Heavy Rainfall Warning Process (RAVAKE) research project that aims to develop Heavy Rainfall nowcasting system.