Rainfall estimates from radar vs. raingauge measurements. Warsaw case study

Contemporary models of urban hydrology and especially hydrodynamic models of stormwater systems demand on supply with high resolution spatial and temporal precipitation information. A plausible solution of precipitation information acquiring over urban catchments is seen in coupling of radar signals and raingauge networks measurements. Suitability of this approach is tested in the case of standard C-band weather radar and the dense network of fast-response raingauges. Rainfall rate estimated based on dependence on the reflectivity factor (Z-R relationship) in single pixels of the radar image are compared to rainfall rates measured by 25 raingauges located in Warsaw, Poland. In the analyzed period, 23 precipitation days with rain from convective clouds and cloud systems are detected. The main conclusion is that despite the fact that adopted Z-R relationship holds well in statistical sense (i.e. the whole period long empirical probability distribution functions (PDFs) of estimated and measured rainfall rates are in good agreement), instantaneous measurements and estimates as well as short-term (one day) PDFs differ remarkably. These differences are not systematic, they vary from the raingauge to raingauge and from day to day. Moreover, the most remarkable differences are associated with the highest rainrates which should be carefully considered prior radar data use as input for urban hydrology modelling.