Use of a weather radar for the hydrology of a mountainous area .1. Radar measurement interpretation

This paper addresses rainfall radar measurement in mountainous areas where numerous catchments subject to flash flooding are located. The main sources of error affecting the quantitative use of weather radar data are examined with special attention paid to the influence of topography and altitude. A radar in a mountainous region is affected by specific measurement errors such as beam blockage; other sources of error like bright band interception can be enhanced by the effect of altitude, This work is based on data collected during the 86-88 Cevennes Experiment conducted in a mountainous Mediterranean region in the south of France prone to Bash floods, Analysis of the main sources of error leads to the following observations. Beam blockage can be corrected using digital terrain models with the correction efficiency depending on the accuracy of the radar antenna pointing direction. The influence of vertical variations in radar reflectivity is shown to be taken into account at an hourly time step in order to provide satisfactory range-dependent corrections. Additionally, the control of the stability of the radar signal using strong ground clutter is described. Because of attenuation effects, the use of a 10-cm wavelength is recommended for surveying intense rain events which regularly affect Mediterranean regions, The error due to an unadapted Z-R relationship is shown to depend on the statistical distribution of reflectivity over the catchment where the rainfall measurement is utilized. (C) 1997 Elsevier Science B.V.