Strong Dependence of Extreme Convective Precipitation Intensities on Gauge Network Density

Extreme convective precipitation on subhourly scales is notoriously misrepresented in rain gauge-based observations, but uncertainties are weakly quantified at the 1 to 30km scale. We employ a unique observing network, the high-density WegenerNet and surrounding operational rain gauge network in southeastern Austria, to sample convective precipitation extremes at these scales. By systematically constructing lower-density networks, we explore how estimated maximum area precipitation depends on observing station density. Using subhourly to hourly temporal resolution, we find a d(-0.5(0.1)) power law decay of the event maximum area precipitation over distances d from 1 to 30km, showing that operational gauge networks underrate extreme convective precipitation falling over small areas. Furthermore, extremes at point scale are found underestimated by operational networks by about 20%. We consider the dependencies representative for short-duration convective events over similar regions at midlatitudes and the results valuable for high-resolution climate model evaluation. Plain Language Summary Precipitation is commonly measured using rain gauge networks. For many applications it is relevant how much precipitation fell over a given area, which is often approximated from point-scale gauge observations. In operational networks, gauges are usually 10km or more apart. This spacing is not sufficient to observe extreme rain intensities in summer convective events, which occur on subhourly time scales and over small areas. Sparse gauge observations lead to high uncertainty in the estimated area precipitation from such events, hampering, for example, damage risk assessments. The WegenerNet Feldbach region in southeastern Austria is one of the densest networks worldwide, with 150 rain gauges within an area of just 300km(2). We use this as core network to explore how maximum area precipitation in convective events depends on the density of the gauge network. We find strong spatial dependence showing that maximum area precipitation observed at 5-6km gauge separation distance is less than 50% of the maximum intensity observed at point scale. We demonstrate that extreme convective precipitation is underestimated in operational networks. The derived spatial dependence curves illustrate the concentrated nature of convective extremes and are valuable for evaluating climate models and interpreting rain gauge-derived precipitation data sets.