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Hydrology and Earth System Sciences An interactive open-access journal of the European Geosciences Union
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Volume 22, issue 1
Hydrol. Earth Syst. Sci., 22, 567-580, 2018
https://doi.org/10.5194/hess-22-567-2018
© Author(s) 2018. This work is distributed under
the Creative Commons Attribution 4.0 License.
Hydrol. Earth Syst. Sci., 22, 567-580, 2018
https://doi.org/10.5194/hess-22-567-2018
© Author(s) 2018. This work is distributed under
the Creative Commons Attribution 4.0 License.

Research article 23 Jan 2018

Research article | 23 Jan 2018

Dominant effect of increasing forest biomass on evapotranspiration: 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 Fernando Jaramillo et al.
  • 1Department of Biological and Environmental Sciences, University of Gothenburg, 40530 Gothenburg, Sweden
  • 2Department of Physical Geography, Stockholm University, 106 91, Stockholm, Sweden
  • 3Stockholm Resilience Center, Stockholm University, 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, 601 76 Norrköping, Sweden
  • 6Department of Forest Ecology and Management, Swedish University of Agricultural Sciences, 750 07 Umeå, Sweden
  • 7Faculty of Earth and Life Sciences, University of Amsterdam, 1081 HV, Amsterdam, the Netherlands
  • 8Department of Earth Sciences, Uppsala University, 75236, Uppsala, Sweden

Abstract. During the last 6 decades, forest biomass has increased in Sweden mainly due to forest management, with a possible increasing effect on evapotranspiration. However, increasing global CO2 concentrations may also trigger physiological water-saving responses in broadleaf tree species, and to a lesser degree in some needleleaf conifer species, inducing an opposite effect. Additionally, changes in other forest attributes may also affect evapotranspiration. In this study, we aimed to detect the dominating effect(s) of forest change on evapotranspiration by studying changes in the ratio of actual evapotranspiration to precipitation, known as the evaporative ratio, during the period 1961–2012. We first used the Budyko framework of water and energy availability at the basin scale to study the hydroclimatic movements in Budyko space of 65 temperate and boreal basins during this period. We found that movements in Budyko space could not be explained by climatic changes in precipitation and potential evapotranspiration in 60% of these basins, suggesting the existence of other dominant drivers of hydroclimatic change. In both the temperate and boreal basin groups studied, a negative climatic effect on the evaporative ratio was counteracted by a positive residual effect. The positive residual effect occurred along with increasing standing forest biomass in the temperate and boreal basin groups, increasing forest cover in the temperate basin group and no apparent changes in forest species composition in any group. From the three forest attributes, standing forest biomass was the one that could explain most of the variance of the residual effect in both basin groups. These results further suggest that the water-saving response to increasing CO2 in these forests is either negligible or overridden by the opposite effect of the increasing forest biomass. Thus, we conclude that increasing standing forest biomass is the dominant driver of long-term and large-scale evapotranspiration changes in Swedish forests.

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Which is the dominant effect on evapotranspiration in northern forests, an increase by recent forests expansion or a decrease by the 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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