Modelling the hydrology of North American Prairie watersheds is complicated because of the existence of numerous landscape depressions that vary in storage capacity. The Soil and Water Assessment Tool (SWAT) is a widely applied model for long‐term hydrological simulations in watersheds dominated by agricultural land uses. However, several studies show that the SWAT model has had limited success in handling prairie watersheds. In past works using SWAT, landscape depression storage heterogeneity has largely been neglected or lumped. In this study, a probability distributed model of depression storage is introduced into the SWAT model to better handle landscape storage heterogeneity. The work utilizes a probability density function to describe the spatial heterogeneity of the landscape depression storages that was developed from topographic characteristics. The integrated SWAT–PDLD model is tested using datasets for two prairie depression dominated watersheds in Canada: the Moose Jaw River watershed, Saskatchewan; and the Assiniboine River watershed, Saskatchewan. Simulation results were compared to observed streamflow using graphical and multiple statistical criterions. Representation of landscape depressions within SWAT using a probability distribution (SWAT–PDLD) provides improved estimations of streamflow for large prairie watersheds in comparison to results using a lumped, single storage approach. Copyright © 2016 John Wiley & Sons, Ltd.

Landscape-scale hydrological models can be improved by incorporating realistic, process-oriented plant models for simulating crops, perennial grasses and woody species. The objective of this project was to present some approaches for plant modelling applicable to daily time step hydrological transport models, such as SWAT. Accurate simulation of plant growth can improve the accuracy of simulations of hydrological and biogeochemical cycles. First, we describe some unique aspects of the general plant model ALMANAC. Next, we describe a modification of the original ALMANAC model used to simulate complex successional vegetation changes in the years following disturbance of a variety of different forest ecosystems, such as forest fires, clear cuts and insect infestations. Finally, we discuss alternative physiological and physical process simulation techniques of plant growth that could increase simulation accuracy in landscape-scale hydrological and transport models such as SWAT.Key words Beer's law; forestry modelling; leaf area index; plant simulation; radiation use efficiency Simulation de croissance végétale au service de la modélisation hydrologique a l'échelle du paysage Résumé Les modèles hydrologiques qui fonctionnent à l'échelle du paysage peuvent être améliorés en incorporant des modèles de plante réalistes orientés sur les processus pour simuler les cultures, les prairies permanentes et les espèces ligneuses. Ce projet a eu pour but de présenter quelques approches de modélisation des plantes intégrables au sein de modèles hydrologiques à pas de temps journalier, comme le modèle SWAT. Une simulation précise de la croissance végétale peut améliorer la précision des simulations des cycles hydrologiques et biogéochimiques. Nous commençons en décrivant quelques aspects originaux du modèle végétal général ALMANAC. Puis nous décrivons une modification de la version originale d'ALMANAC pour simuler des changements complexes de succession végétale au cours des années qui suivent la perturbation d'un écosystème forestier, comme un incendie de forêt, une coupe claire ou une infestation d'insecte. Finalement, nous discutons quelques techniques alternatives pour simuler les processus physiologiques et physiques de la croissance végétale qui pourraient améliorer la précision des simulations de végétation dans les modèles hydrologiques à l'échelle du paysage comme SWAT.

Several modifications were made to the Soil and Water Assessment Tool (SWAT) to better represent processes occurring within forested watersheds on the Boreal Plain in Canada. The modified model, called SWATBF, was applied to the Willow Creek watershed (15.1 km2) in north central Alberta. The performance of the model for the calibration period (2001–2003) was good with coefficients of efficiency of 0.89 and 0.81 being achieved for the prediction of monthly and daily runoff, respectively. However, it was found that SWATBF did not perform as well for the validation period (2004–2006) with the monthly and daily coefficients of efficiency being 0.44 and 0.27, respectively. Potential sources of error to explain the decline in model performance for the validation period are discussed. SWATBF has the potential to be used as a tool by forest managers for predicting the effects of land use change on the Boreal Plain provided that it can be satisfactorily validated.

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