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.

Published in

Hydrology and Earth System Sciences
2018, Volume: 22, number: 1, pages: 567-580
Publisher: COPERNICUS GESELLSCHAFT MBH

SLU Authors

• Cory, Neil

  • Department of Forest Resource Management, Swedish University of Agricultural Sciences
    

• Laudon, Hjalmar

  • Department of Forest Ecology and Management, Swedish University of Agricultural Sciences
    

Sustainable Development Goals

SDG7 Ensure access to affordable, reliable, sustainable and modern energy for all


UKÄ Subject classification

Forest Science


Publication identifier

DOI: https://doi.org/10.5194/hess-22-567-2018

Permanent link to this page (URI)

https://res.slu.se/id/publ/93710