![]() ![]() The most likely reason for this is the use of a fixed Z– R relationship when estimating rainfall rates ( R) from reflectivity ( Z), which fails to account for natural variations in raindrop size distribution with intensity. As a result, peak rainfall intensities were severely underestimated (factor 1.8–3.0 or 44 %–67 %). ![]() Despite being adjusted for bias by gauges, five out of six radar products still exhibited a clear conditional bias, with intensities of about 1 %–2 % per mmh −1. Differences in sampling volumes between radar and gauges play an important role in explaining the bias but are hard to quantify precisely due to the many post-processing steps applied to radar. However, after taking into account the different sampling volumes of radar and gauges, actual biases could be as low as 10 %. Results show that the overall agreement in heavy rain is fair (correlation coefficient 0.7–0.9), with apparent multiplicative biases on the order of 1.2–1.8 (17 %–44 % underestimation). The top 50 events in a 10-year database of radar data were used to quantify the overall agreement between radar and gauges as well as the bias affecting the peaks. In total, six different radar products in Denmark, the Netherlands, Finland and Sweden were considered. The work is performed within the context of the joint experiment framework of project MUFFIN (Multiscale Urban Flood Forecasting), which aims at better understanding the link between rainfall and urban pluvial flooding across scales. This study sheds new light on current performances by conducting a multinational assessment of radar's ability to capture heavy rain events at scales of 5 min up to 2 h. However, since there is no common benchmark, improvements are hard to quantify objectively. Each country has developed its own strategy for addressing this issue. The hope is that by measuring at higher resolutions and making use of dual-polarization radar, these mismatches can be reduced. ![]() The most important of them is that radar tends to underestimate rainfall compared to gauges. However, when it comes to accurately measuring small-scale rainfall extremes responsible for urban flooding, many challenges remain. Weather radar has become an invaluable tool for monitoring rainfall and studying its link to hydrological response. ![]()
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