Abstract
Vegetation has a substantial impact on the local climate. Land cover changes through afforestation or deforestation can amplify or mitigate climate warming by changes in biophysical and biogeochemical mechanisms. In the montane to subalpine area of the Eastern Alps in Europe, where forests have constantly expanded in the last four decades, data of meteorological stations show a consistent reduction in incoming global radiation for the period 2000–2015. To assess the potential role of forests in contributing to such a reduction, three site pairs in Central Europe with neighbouring forest and non-forest sites were analysed. In all the pairs, a lower amount of incoming radiation was recorded at the forest site. When biophysical mechanisms such as albedo, surface roughness and Bowen ratio changes were modelled together with changes in global radiation, the total radiative forcing accounted for a rate of change in air temperature was equal to 0.032 °C ± 0.01 °C per Wm−2. These results suggest that local climate is influenced by land cover change through afforestation both via albedo and radiation feedbacks but also by means of indirect biophysical and species-dependent mechanisms. The data obtained for the site pairs in Central Europe are finally discussed to infer the occurrence of similar forest-driven effects in the Eastern Alps which may explain part of the solar dimming observed in high elevation weather stations.
Highlights
Mountain forests occupy approximately one fourth of the global forests (Price et al 2011) and represent the predominant land cover of European mountains, covering 41% of the total land area
Global radiation (G) measured at montane to sub-alpine zone stations in Trentino consistently decreased over the period 2000–2015 (figure 2(b)), confirming previous observations made for a shorter period of time by HG site pair was equivalent to 35 Wm−2 for clear sky irradiance
A robust indication of this study is that forest-driven dimming effects are detectable and hold for both, broadleaf (European beech at Hainich) and coniferous forests (Norway spruce at Tharandt and Scots pine at Loobos)
Summary
Mountain forests occupy approximately one fourth of the global forests (Price et al 2011) and represent the predominant land cover of European mountains, covering 41% of the total land area (www.eea.europa. eu). While modelling studies mostly showed a positive elevationdependent warming (i.e Rangwala et al 2015, Kotlarski 2015, Wang et al 2016), a number of observational studies demonstrated that the recent rate of increase in air temperature measured by weather stations, can be higher at low compared to high elevations in different mountain ranges (Philipona 2013, Kirchner et al 2013, Zeng et al 2015, Tudoroiu et al 2016). Such negative elevation-dependent warming (EDW) was interpreted as a consequence of ‘solar brightening’ (increasing global radiation) at low elevations. This was probably triggered by an improved air quality in the most populated areas of the mountain regions (Philipona 2013, Zeng et al 2015, Tudoroiu et al 2016)
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