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 co verage. Some scepticism exists in the hydrological community as to the accu racy of radar rainfall estimates. In an attempt to address some of the prob lems in estimating rainfall by radar, these two kinds of measurement can be integrated to provide a better spatial rainfall field. A new integration a pproach is presented, that makes use of the radar-determined wetted-area ra tio 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 smalt. The algorit hm was applied to significant rainfall events between October 1995 and Febr uary 1996 for the Liebenbergsvlei catchment using a dense rain-gauge networ k of up to 45 gauges. Using the network to adjust the radar rainfall reduce d the radar-gauge ratio from 1.13 to 1.04. By integrating the radar and rai n-gauge information, the standard error of daily radar rainfall estimates o ver the catch ment was reduced from 7.8 mm to less than 2.0 mm compared to that from the dense rain-gauge network.