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Volume 21, issue 10 | Copyright
Hydrol. Earth Syst. Sci., 21, 5385-5399, 2017
https://doi.org/10.5194/hess-21-5385-2017
© Author(s) 2017. This work is distributed under
the Creative Commons Attribution 3.0 License.

Research article 27 Oct 2017

Research article | 27 Oct 2017

Regional frequency analysis of extreme rainfall in Belgium based on radar estimates

Edouard Goudenhoofdt1, Laurent Delobbe1, and Patrick Willems2 Edouard Goudenhoofdt et al.
  • 1The Royal Meteorological Institute of Belgium, Brussels, Belgium
  • 2Department of Civil Engineering – Hydraulics Division, University of Leuven, Leuven, Belgium

Abstract. In Belgium, only rain gauge time series have been used so far to study extreme rainfall at a given location. In this paper, the potential of a 12-year quantitative precipitation estimation (QPE) from a single weather radar is evaluated. For the period 2005–2016, 1 and 24h rainfall extremes from automatic rain gauges and collocated radar estimates are compared. The peak intensities are fitted to the exponential distribution using regression in Q-Q plots with a threshold rank which minimises the mean squared error. A basic radar product used as reference exhibits unrealistic high extremes and is not suitable for extreme value analysis. For 24h rainfall extremes, which occur partly in winter, the radar-based QPE needs a bias correction. A few missing events are caused by the wind drift associated with convective cells and strong radar signal attenuation. Differences between radar and gauge rainfall values are caused by spatial and temporal sampling, gauge underestimations and radar errors. Nonetheless the fit to the QPE data is within the confidence interval of the gauge fit, which remains large due to the short study period. A regional frequency analysis for 1h duration is performed at the locations of four gauges with 1965–2008 records using the spatially independent QPE data in a circle of 20km. The confidence interval of the radar fit, which is small due to the sample size, contains the gauge fit for the two closest stations from the radar. In Brussels, the radar extremes are significantly higher than the gauge rainfall extremes, but similar to those observed by an automatic gauge during the same period. The extreme statistics exhibit slight variations related to topography. The radar-based extreme value analysis can be extended to other durations.

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Knowing the characteristics of extreme precipitation is useful for flood management applications like sewer system design. The potential of a 12-year high-quality weather radar precipitation dataset is investigated by comparison with rain gauges. Despite known limitations, a good agreement is found between the radar and the rain gauges. Using the radar data allow us to reduce the uncertainty of the extreme value analysis, especially for short duration extremes related to thunderstorms.
Knowing the characteristics of extreme precipitation is useful for flood management applications...
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