On the Impact of Tree-Line Expansion: A Threat to Hydropower Resources?

Centuries of mountain farming and forestry have caused the treeline in Norway to be situated up to hundreds of meters below its climatic potential. With climate change further raising this potential, vast areas of mountainous Norway are becoming open to tree growth. This shift in land cover significantly alters the hydrological balance, as trees typically have higher evapotranspiration rates than the vegetation they replace. Given that Norway’s power mix is largely dominated by hydropower, these changes in hydrology pose a potential threat to energy production.

To quantify the impact of this shift, we employ a high-resolution coupled atmosphere-land model (WRF-CTSM) using current and projected vegetation maps from the Natural History Museum in Oslo.

As the evapotranspiration (ET) levels in Norway are currently not well-constrained targeted fieldwork with mobile eddy covariance towers is being conducted to measure turbulent fluxes in representative areas. This data will be used to update the model's plant functional types to better represent the local vegetation.

The updated model will then be run under different SSP scenarios to provide more robust estimates of current and future ET levels in Norway and their potential impact on hydropower production.