Calibration of the Parameters of a Rainfall-Runoff Model in Ungauged Basins Using Synthetic Flow Duration Curves as Estimated by Regional Analysis

Abstract

The knowledge of hydrologic variables and related functions at a given river cross section, as well as its time series of daily mean flows, supports the planning, design, and operation of facilities for the use of water resources in gauged river basins. In basins lacking systematic records of water levels and discharges, however, it becomes necessary to develop methodologies that enable the transfer of hydrologic information that is available in other basins. The present study proposes and evaluates a method for the automatic calibration of the parameters of a rainfall-runoff model in ungauged basins, using synthetic long-term flow duration curves (FDCs) estimated by a regional statistical model as the paradigm for the hydrologic processes. In this context, the long-term flow duration curves are used as an instrument to calibrate the parameters of a conceptual rainfall-runoff model. Once the parameters that control the hydrologic synthesis by the rainfall-runoff model are estimated, the continuous simulation of discharges over a given period of time enables various hydrologic evaluations such as the frequency analysis of rare events, the water balance of reservoirs, flow routing, and water availability studies. The methodology shown in here is composed, basically, of two parts. In the first part, a method for the regionalization of long-term flow duration curves is proposed, thus enabling the transfer of these hydrologic functions to ungauged watersheds, provided these are located in the same homogenous region as that of the basins for which data are available. In the second stage, the calibration of the parameters of the RIO GRANDE rainfall-runoff model is performed, having as a target to simulate the flow duration curves synthesized by the regional statistical model. The method was applied to a number of watersheds located in southeastern Brazil. In both phases of the proposed method, some performance indices are calculated in order to evaluate the accuracy of the procedures involved.