Links between Nordic and Arctic hydroclimate and vegetation changes : Contribution to possible landscape-scale nature-based solutions

In Nordic and Arctic regions, the rapidly warming climate sustains hydroclimatic and vegetation changes in the landscape. There is evidence for an increase in vegetation density in some regions, a trend that is expected as a response to increasing temperature and precipitation. If the hydroclimatic changes are linked to vegetation response, it could be viewed as a landscape-scale nature-based solution (NBS) that could moderate the runoff response, as denser vegetation should lead to increased evapotranspiration and lower runoff. In this paper, we investigate and compare hydroclimatic changes over a set of basins in the Nordic region and northwest America and compare with changes in vegetation density, analyzed using the normalized difference vegetation index (NDVI) for three time periods: 1973-1978, 1993-1998, and 2013-2016. Over the period of the 1970s to 1990s, the hydroclimate became warmer and wetter and vegetation density increased, but over a later period from the 1990s to 2010s, vegetation density decreased, despite a continuing warming and wetting of the climate. Although there was a tendency for runoff to decrease in basins where vegetation density increased, the relation between precipitation and runoff was much stronger. Overall, we found weak evidence for vegetation density changes, driven by hydroclimate, to act as NBS on the landscape scale over the studied regions. However, as hydroclimatic changes interact with vegetation changes and their ensuing hydrological responses in complex ways, more detailed investigations are needed to determine the potential NBS effect on the landscape scale across Nordic and Arctic regions