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Hydrology and Earth System Sciences An interactive open-access journal of the European Geosciences Union
https://doi.org/10.5194/hess-2017-347
© Author(s) 2017. This work is distributed under
the Creative Commons Attribution 4.0 License.
Research article
22 Jun 2017
Review status
This discussion paper is a preprint. A revision of this manuscript was accepted for the journal Hydrology and Earth System Sciences (HESS) and is expected to appear here in due course.
The effect of northern forest expansion on evapotranspiration overrides that of a possible physiological water saving response to rising CO2: Interpretations of movement in Budyko Space
Fernando Jaramillo1,2,3, Neil Cory4, Berit Arheimer5, Hjalmar Laudon6, Ype van der Velde7, Thomas B. Hasper1, Claudia Teutschbein8, and Johan Uddling1 1Department of Biological and Environmental Sciences, University of Gothenburg, SE–40530 Gothenburg, Sweden
2Department of Physical Geography, Stockholm University, SE–106 91, Stockholm, Sweden
3Stockholm Resilience Center, Stockholm University, SE–106 91, Stockholm, Sweden
4Department of Forest Resource Management; Division of Forest Resource Data, Swedish University of Agricultural Sciences, Umeå, Sweden
5Swedish Meteorological and Hydrological Institute, SE-601 76 Norrköping, Sweden
6Department of Forest Ecology and Management, Swedish University of Agricultural Sciences, SE-750 07 Umeå, Sweden
7Faculty of Earth and Life Sciences, University of Amsterdam, 1081 HV, Amsterdam, the Netherlands
8Department of Earth Sciences, Uppsala University, SE-75236, Uppsala, Sweden
Abstract. During the last six decades, forest biomass has expanded in the Northern basins, mainly due to forest management. This expansion should imply an increasing effect on evapotranspiration. However, increasing global CO2 emissions also trigger physiological plant water saving responses that induce an opposite effect on evapotranspiration. The dominant long-term and large-scale effect on evapotranspiration is still a matter of debate. In this study, we determined the dominant effect on evapotranspiration in Northern forests during the period 1961–2012 by studying change-effects on the ratio of actual evapotranspiration to precipitation, known as the evaporative ratio. We used the Budyko framework of water and energy availability at the basin scale to study the hydroclimatic movements in Budyko space of 65 Swedish basins. We found that changes in the evaporative ratio in 60 % of these basins could not be explained by climatic changes in precipitation and potential evapotranspiration. In both the temperate and boreal basin groups studied, a positive residual effect on the evaporative ratio counteracted the negative climatic effect. Furthermore, temporal change of this residual effect during the period 1961–2012 agreed with that of the standing forest biomass in both the temperate and boreal basin groups as well as with that of the forest cover area in the temperate group. Hence, our long-term and regional-scale results indicate that a positive effect on evapotranspiration from the increasing forest biomass overrode any possible negative stomatal water saving response from increasing atmospheric carbon dioxide concentration. Thus, we suggest that forest expansion is the dominant driver of long-term and large-scale evapotranspiration changes in Northern forests.

Citation: Jaramillo, F., Cory, N., Arheimer, B., Laudon, H., van der Velde, Y., Hasper, T. B., Teutschbein, C., and Uddling, J.: The effect of northern forest expansion on evapotranspiration overrides that of a possible physiological water saving response to rising CO2: Interpretations of movement in Budyko Space, Hydrol. Earth Syst. Sci. Discuss., https://doi.org/10.5194/hess-2017-347, in review, 2017.
Fernando Jaramillo et al.
Fernando Jaramillo et al.

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Which is the dominant effect on evapotranspiration in Northern forests, an increase by recent forests expansion or a decrease as a water use response due to increasing CO2 concentrations? We determined the dominant effect during the period 1961–2012 in 65 Swedish basins. We used the Budyko framework to study the hydroclimatic movements in Budyko space. Our findings suggest that forest expansion is the dominant driver of long-term and large-scale evapotranspiration changes.
Which is the dominant effect on evapotranspiration in Northern forests, an increase by recent...
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