Improving Hydrometeorological Forecasting Using High-Resolution X-Band Radars (HyFoX)
Atmospheric Science
Final Report Abstract
The overall topic of the project Improving Hydrological Forecasting Using High-Resolution X-Band Radars (HyFoX) was the investigation of the impact of high-resolution weather radar observations on hydrological modelling and flash flood forecasting in comparison to and in complementation of C-band radars. The aims of the project were to examine whether higher resolution from X-band radar, especially in time, could outperform more precise precipitation estimates from polarimetric C-band radar and if a network of overlapping X-band radars is needed or less accurate precipitation estimates from single X-band radars are sufficient for hydrometeorological forecasting. Three different environments should have been investigated (a flat rural region in Northern Germany, the flat urban area of Hamburg and the mountainous city of Barcelona, Spain) to examinei n which kinds of environment single or networks of X-band radars can improve hydrometeorological forecasting. All three regions were also covered by C-band radars operated by national weather services allowing for investigating the benefit of a combination of X-band radars with C-band networks for hydrometeorological forecasting in flood-prone areas. During the first phase of the project, preliminary simulations with hydrological and hydraulic models in the regions of Barcelona and Hamburg revealed that large discrepancies between datasets from rain gauges, X- and C-band radars existed leading also to large differences in runoff simulations. This discrepancy in the datasets is mainly caused by attenuation due to liquid water. The magnitude of attenuation is generally inversely proportional to the wavelength, i.e. observations from X-band radars are more affected by attenuation than those from C-band radars. Therefore, the objective of the project had to be adjusted by shifting the focus to attenuation correction in the X-band radar observations to ensure for reliable input data for the simulations. In total six algorithms for attenuation correction in single X-band radars were investigated: A classical well known approach that is known to become unstable in heavy precipitation, three variations of this algorithm using different ways to prevent it from getting unstable and two method that combine X- and C-band radar observations. From this study conclusions can be drawn that using additional information from less attenuated radar systems lead to best results. Corrected X-band radar data have been used as input for a runoff simulation of an event on 5 May 2015 with the hydrological model KALYPSO-NA in collaboration with the BMBF-project StucK (Sicherstellung küstennaher, urbaner Räume unter Berücksichtigung des Klimawandels). Simulations were compared to observations of two water level stations. At one station simulations with rain gauge data show best results whereas simulations with both radar types underestimate the measured runoff. At the other station simulations with X-band radar data are in very good agreement with the measured water levels and outperform simulations with C-band. Simulations with rain gauge data overestimate runoff measurements almost by a factor of three. This shows the potential of local observations of precipitation, but a larger number of events is needed to make a statement about the advantages and disadvantages of using high resolution weather radar data in hydrological modelling.
Publications
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(2018) Intercomparison of attenuation correction algorithms for single-polarized X-band radars. Atmospheric Research 201 116–132
Lengfeld, K.; Berenguer, M.; Sempere Torres, D.
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(2018) The Hamburg Tornado (7 June 2016) from the perspective of low-cost high-resolution radar data and weather forecast model. Atmospheric Research 211 1–11
Hoffmann, Peter; Merker, Claire; Lengfeld, Katharina; Ament, Felix
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Comparison of Attenuation Correction Algorithms for Single-Polarized X-Band Radars (AMS 38th Conference on Radar Meteorology to be held in Chicago, August 28 - September 1, 2017)
Lengfeld, K., Berenguer, M. and Sempere-Torres, D.
