Abstract
Abstract. Vegetation is known to have strong influence on evapotranspiration (ET), a major component of terrestrial water balance. Yet hydrological models often describe ET by methods unable to include the variability of vegetation characteristics in their predictions. To take advantage of the increasing availability of high-resolution open GIS data on land use, vegetation and soil characteristics in the boreal zone, a modular, spatially distributed model for predicting ET and other hydrological processes from grid cell to catchment level is presented and validated. An improved approach to upscale stomatal conductance to canopy scale using information on plant type (conifer/deciduous) and stand leaf-area index (LAI) is proposed by coupling a common leaf-scale stomatal conductance model with a simple canopy radiation transfer scheme. Further, a generic parametrization for vegetation-related hydrological processes for Nordic boreal forests is derived based on literature and data from a boreal FluxNet site. With the generic parametrization, the model was shown to reproduce daily ET measured using an eddy-covariance technique well at 10 conifer-dominated Nordic forests whose LAI ranged from 0.2 to 6.8 m2 m−2. Topography, soil and vegetation properties at 21 small boreal headwater catchments in Finland were derived from open GIS data at 16 m × 16 m grid size to upscale water balance from stand to catchment level. The predictions of annual ET and specific discharge were successful in all catchments, located from 60 to 68∘ N, and daily discharge was also reasonably well predicted by calibrating only one parameter against discharge measurements. The role of vegetation heterogeneity in soil moisture and partitioning of ET was demonstrated. The proposed framework can support, for example, forest trafficability forecasting and predicting impacts of climate change and forest management on stand and catchment water balance. With appropriate parametrization it can be generalized outside the boreal coniferous forests.
Highlights
The boreal region, encompassing ca. 12 % of world’s land area, is characterized by a mosaic of peatlands, lakes and forests of different ages and structures
A generic parametrization for vegetation-related hydrological processes for Nordic boreal forests is derived based on literature and data from a boreal FluxNet site
Improving ET description by a more physiologically phased approach could be proposed as one potential area to reduce uncertainties in predictions of the hydrological budget and resulting streamflow and soil moisture patterns. Motivated both by scientific needs and potential practical applications, this study addresses two independent but interrelated objectives: first, we develop a generic model for daily ET in boreal forest and peatland ecosystems and explore how daily and annual ET can be predicted based on plant functional traits, canopy leafarea index (LAI), and open data on landscape structure and meteorological forcing
Summary
The boreal region, encompassing ca. 12 % of world’s land area, is characterized by a mosaic of peatlands, lakes and forests of different ages and structures. Understanding spatial and temporal patterns of hydrological fluxes and state variables is becoming increasingly important in the context of intensifying the use of boreal forests under the pressures of climate change (Bonan, 2008; Gauthier et al, 2015; Price et al, 2013; Spittlehouse, 2005; Laudon et al, 2016). Model approaches that can effectively utilize available environmental data, open highresolution GIS data and remote-sensing products for hydrological predictions are necessary for climate-smart and environmentally sustainable use of boreal ecosystems (Mendoza et al, 2002). Diverse modeling approaches are used to predict pointscale, catchment and regional hydrological balance, which reflects the broad spectrum of practical needs and research questions addressed, as well as historical development of hydrological models.
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