Scale Interactions in Radar Rainfall Estimation Uncertainty

Abstract

This study formulates an experimental strategy that couples rainfall observations from a locally deployed mobile X-band dual polarization radar with recording rain gauge measurements to create an error assessment of the spatio-temporal variability of high-resolution gridded rainfall fields. We discuss the trade-offs and values in the radar-rainfall uncertainty associated with different measurement resolutions. Overall, we found that radar measurement errors naturally decrease with averaging in space and time, but there is a generally negative value associated with the increase in spatial scale from 300 m to 5 km. Spatial averaging of radar rainfall increased the probability of detection slightly by 4%. However the decrease in relative root-mean-squared error (R-RMSE) was negligible as the false alarm rate increased by 10% and the Heidke skill score reduced by 16%. In terms of reducing measurement uncertainty, there was greater overall value by averaging temporally up to 60 min than averaging spatially to 5 km, where R-RMSE decreased up to 40%, probability of detection increased by 5%, false alarm ratio decreased by 14%, and the Heidke skill score increased by 7%. However the value added in spatio-temporal integration is dependent on the usage of the rainfall data as important information on the natural variability of rainfall gets lost with averaging in time and space.