Abstract
Abstract. This study aims to decipher the interactions of a precipitation post-processor and several other tools for uncertainty quantification implemented in a hydrometeorological forecasting chain. We make use of four hydrometeorological forecasting systems that differ by how uncertainties are estimated and propagated. They consider the following sources of uncertainty: system A, forcing, system B, forcing and initial conditions, system C, forcing and model structure, and system D, forcing, initial conditions, and model structure. For each system's configuration, we investigate the reliability and accuracy of post-processed precipitation forecasts in order to evaluate their ability to improve streamflow forecasts for up to 7 d of forecast horizon. The evaluation is carried out across 30 catchments in the province of Quebec (Canada) and over the 2011–2016 period. Results are compared using a multicriteria approach, and the analysis is performed as a function of lead time and catchment size. The results indicate that the precipitation post-processor resulted in large improvements in the quality of forecasts with regard to the raw precipitation forecasts. This was especially the case when evaluating relative bias and reliability. However, its effectiveness in terms of improving the quality of hydrological forecasts varied according to the configuration of the forecasting system, the forecast attribute, the forecast lead time, and the catchment size. The combination of the precipitation post-processor and the quantification of uncertainty from initial conditions showed the best results. When all sources of uncertainty were quantified, the contribution of the precipitation post-processor to provide better streamflow forecasts was not remarkable, and in some cases, it even deteriorated the overall performance of the hydrometeorological forecasting system. Our study provides an in-depth investigation of how improvements brought by a precipitation post-processor to the quality of the inputs to a hydrological forecasting model can be cancelled along the forecasting chain, depending on how the hydrometeorological forecasting system is configured and on how the other sources of hydrological forecasting uncertainty (initial conditions and model structure) are considered and accounted for. This has implications for the choices users might make when designing new or enhancing existing hydrometeorological ensemble forecasting systems.
Highlights
Reliable and accurate hydrological forecasts are critical to several applications such as preparedness against floodrelated casualties and damages, water resources management, and hydropower operations (Alfieri et al, 2014; Bogner et al, 2018; Boucher et al, 2012; Cassagnole et al, 2021)
Is precipitation post-processing needed in order to improve streamflow forecasts when dealing with a forecasting system that fully or partially quantifies many sources of uncertainty? How does the performance of different uncertainty quantification tools compare? how does each uncertainty quantification tool contribute to improving streamflow forecast performance across different lead times and catchment sizes?
The precipitation post-processor undeniably improves the quality of precipitation forecasts (Figs. 4 and 5), our results suggest that a modeling system that only tackles the quantification of forcing uncertainties with a precipitation post-processor is insufficient to produce reliable and accurate streamflow forecasts (Figs. 6–8)
Summary
Reliable and accurate hydrological forecasts are critical to several applications such as preparedness against floodrelated casualties and damages, water resources management, and hydropower operations (Alfieri et al, 2014; Bogner et al, 2018; Boucher et al, 2012; Cassagnole et al, 2021). The inherent uncertainty of hydrological forecasts stems from four main sources: (1) observations, (2) the hydrological model structure and parameters, (3) the initial hydrological conditions, and (4) the meteorological forcing Valdez et al.: Post-processing precipitation forecasts and many sources of hydrological uncertainty
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