The characteristic time scale for basin hydrological response using radar data

The transformation of rainfall into runoff at a basin outlet is the combine d effect of many hydrological processes, which occur at a wide range of spa tial and temporal scales. However, determining the scale of the combined hy drological response of the basin is still problematic and concepts for its definition are yet to be identified. In this paper high-resolution meteorol ogical radar data are used for the determination of a characteristic tempor al scale for the hydrological response of the basin - the 'response time sc ale' (T-s*). T-s* is defined as the time scale at which the pattern of the time-averaged radar rainfall hietograph is most similar to the pattern of t he measured outlet runoff hydrograph. The existence of such similarity at a relatively stable time scale for a specific basin indicates that it is an intrinsic property of the basin and is related to its hydrological response . The identification of the response time scale is carried out by analysis of observations only, without assuming a specific rainfall-runoff model. T- s* is examined in four small basins (10-100 km(2)) in Israel. The spatial s cale is assumed as the entire basin. For all analyzed basins a stable respo nse time scale is identified. Relatively short time scales are found for th e urban and arid basins (15-30 min), while for the rural basins longer time scale are identified (90-180 min). The issues of relationship between the response time scale and basin properties and modeling at the response time scale have yet to be determined. (C) 2001 Elsevier Science B.V. All rights reserved.