Optimal Hydrological Model Calibration Strategy for Climate Change Impact Studies

Abstract

To assess the impacts of climate change on water resources, hydrological models are the most commonly used to simulate future flows. Hydrological model calibration is typically based on historical hydrometeorological data, which may not be representative of the future climate. This paper evaluates various calibration strategies to minimize this issue. The impact of these calibration strategies is measured on 921 North American catchments using a lumped hydrological model. Five calibration strategies (warm, low rainfall, high rainfall, low-flow, and high-flow years) were investigated, each using a 5-year (noncontinuous) independent validation dataset maximizing all five studied climate anomalies. The remaining years were used as a pool of calibration years, using targeted subsets of years in multiples of five to assess the impact of the number of calibration years versus the climate anomaly of each calibration subset. Results showed large cross-catchment variability, indicating that no single calibration strategy and number of calibration years were optimal for all watersheds. However, the large number of catchments used in this study allows for some general conclusions to be drawn. For the warm-years calibration strategy, using a large number of years was the approach most likely to succeed, indicating that removing a small subset of cold years was preferable to keeping a small subset of warm years. For the other four calibration strategies, the approach most likely to succeed was the one in which about half of the years in the historical record were kept. For the warm year strategy, keeping a larger number of years for calibration ensures better model robustness to account for precipitation variability in the validation set. For the other four calibration strategies, which are mostly related to precipitation, a larger number of years had to be dropped to account for the much larger differences between wet and dry years.