Towards a multi-year urban precipitation climatology at 100 m scale using X-band radar observations

An operational, single-polarized X-band weather radar provides measurements in Hamburg’s city center for almost eight years. This weather radar operates at an elevation angle (~3.5°) with a high temporal (30 s), range (60 m), and sampling (1°) resolution resulting in a high information density within the 20 km scan radius. Studies on short time periods (several months) proofs the performance of this low-cost local area weather radar. For example, a case study on a tornado in a rain event demonstrates its refined resolution compared to the German nationwide C-band radars. Now, we aim for a eight-year precipitation climatology with 100 m resolution. This data set will enable reliable studies on urban extreme precipitation. This presentation will describe how we can infer a precipitation estimate based on multi-year weather radar observations in the urban area of Hamburg.

The single-polarization and small wavelength comes along with high resolution but at the same time high uncertainties. We address several sources of errors affecting the radar-based precipitation estimate, like the radar calibration, alignment, attenuation, noise, non-meteorologial echoes, and Z-R relation. The deployment of additional vertically pointing micro rain radars yields drop size distributions at relevant heights reducing errors effectively concerning the radar calibration and required statistical relations (k-Z and Z-R relation). We outline the performance of the correction methods for long time periods and discuss open issues and limitations.

With this high-quality and -resolution weather radar product, refined studies on the spatial and temporal scale of urban precipitation will be possible. This data set will be used for further hydrological research in an urban area within the project Sustainable Adaption Scenarios for Urban Areas – Water from Four Sides of the Cluster of Excellence Climate Climatic Change, and Society (CliCCS).