Defining the <i>Z–R</i> Relationship Using Gauge Rainfall with Coarse Temporal Resolution: Implications for Flood Forecasting

Abstract

This paper demonstrates a procedure for deriving the Z–R relationship using poor temporal resolution gauge rainfall data and evaluates its impact on runoff forecasting in the upper Ping River Basin in Northern Thailand. The procedure is based on the use of a scaling logic to modify the Z–R relationship calibrated using daily (or other coarse) resolution ground rainfall data. This scaling procedure is demonstrated using daily gauge data and results in radar rainfall estimates that lead to improved runoff simulations and flood forecasts for the upper Ping River Basin compared with the case in which the daily (or raw) Z–R relationship is used or even when the daily gauge rainfall is used alone. This evaluation is based on hourly comparisons for the high rainfall season over a period of 3 years (2004–2006) at six point locations in the catchment. This scaling relationship has significant implications for flood modeling in most of the developing world that has weather radar coverage and a daily gauge network but a limited continuous ground rainfall measuring network.