Streamflow Prediction in Ungauged Basins: Review of Regionalization Methods

This paper presents a comprehensive review of a fundamental and challenging issue in hydrology: the regionalization of streamflow and its advances over the last two decades, specifically 1990–2011. This includes a discussion of developments in continuous streamflow regionalization, model parameter optimization methods, the application of uncertainty analysis in regionalization procedures, limitations and challenges, and future research directions. Here, regionalization refers to a process of transferring hydrological information from gauged to ungauged or poorly gauged basins to estimate the streamflow. Huge efforts have been devoted to regionalization of flood peaks, low flow, and flow duration curves (FDCs) in the literature, while continuous streamflow regionalization is helpful in deriving each of these variables. Continuous streamflow regionalization can be conducted through rainfall-runoff models or hydrologic model–independent methods. In the former case, model parameters are used as instruments to transfer hydrological information from gauged to ungauged basins, whereas the latter case transfers streamflow directly through data-driven methods. According to the reviewed regionalization studies, streamflow regionalization has been done mostly through hydrologic models, whereas the focus of these studies is on identifying the best methods to transfer the model parameters. Conceptual rainfall-runoff models, such as Hydrologiska Byråns Vattenbalansavdelning (HBV) and Identification of Unit Hydrographs and Component Flows from Rainfall, Evaporation and Streamflow Data (IHACRES) have emerged as the most frequently used models in this category. Physiographic attributes (e.g., catchment area, elevation, and slope of basins or channels) and meteorological information (e.g., daily time series of rainfall and temperature) are the most commonly used in the regionalization studies. Diversity in catchment physical attributes and climatic variability produces different performances for each regionalization method’s application in various regions. However, overall, spatial proximity and physical similarity have shown satisfactory performance in arid to warm temperate climate (e.g., Australia) and regression-based methods have been preferred in warm temperate regions (e.g., most European countries). Similarly, in cold and snowy regions (e.g., Canada) spatial proximity and physical similarity approaches seemed to be good options among the hydrologic model–dependent methods. Hydrologic model–independent methods have been applied only in few cases, and the results have indicated that in warm temperate regions linear and nonlinear regression methods perform well.