The integration of daily rain gauge and radar rainfall estimates for the Liebenbergsvlei catchment, northeastern Free State.

Whereas a rain gauge provides an accurate point measurement, radar rainfall estimates describe a rainfall field over large contiguous areas. Radar and rain gauge therefore represent opposite ends of the spectrum of spatial coverage. Some scepticism exists in the hydrological community as to the accuracy of radar rainfall estimates. In an attempt to address some of the problems in estimating rainfall by radar, these two kinds of measurement can be integrated to provide a better spatial rainfall field. A new integration approach is presented, that makes use of the radar-determined wetted-area ratio to establish the effect that rain gauge results have on radar-estimated rainfall. In this manner rain gauges are given greater influence when the wetted area is large and less influence when the area is small. The algorithm was applied to significant rainfall events between October 1995 and February 1996 for the Liebenbergsvlei catchment using a dense rain-gauge network of up to 45 gauges. Using the network to adjust the radar rainfall reduced the radar-gauge ratio from 1.13 to 1.04. By integrating the radar and rain-gauge information, the standard error of daily radar rainfall estimates over the catchment was reduced from 7.8 mm to less than 2.0 mm compared to that from the dense rain-gauge network. [ABSTRACT FROM AUTHOR]