Abstract
ABSTRACT Exacerbated by climate change, Europe has experienced series of hot and dry summer since the beginning of the 21st century. The importance of land conditions became an international concern with a dedicated sustainable development goal (SDG), the SDG 15. It calls for developing and finding innovative solutions to follow and evaluate impacts of changing land conditions induced by various driving forces. In Switzerland, drought risk will significantly increase in the coming decades with severe consequences on agriculture, energy production and vegetation. In this paper, we used a 35-year satellite-derived annual and seasonal times-series of normalized difference water index (NDWI) to follow vegetation water content evolution at different spatial and temporal scales across Switzerland and related them to temperature and precipitation to investigate possible responses of changing climatic conditions. Results indicate that there is a small and slow drying tendency at the country scale with a NDWI mean decreasing slope of −0.22%/year for the 23% significant pixels across Switzerland. This tendency is mostly visible below 2000 m above sea level (m.a.s.l.) and in all biogeographical regions. The Southern Alps regions appear to be more responsive to changing drying conditions with a significant and slight negative NDWI trend (−0.39%/year) over the last 35 years. Moreover, NDWI values are mostly a function of temperature at elevations below the tree line rather than precipitation. Findings suggest that multi-annual and seasonal NDWI can be a valuable indicator to monitor vegetation water content at different scales, but other components such as land cover type and evapotranspiration should be considered to better characterize NDWI variability. Satellite Earth Observations data can provide valuable complementary observations for national statistics on the ecological state of vegetation to support SDG 15 to monitor land affected by drying conditions.
Highlights
Climate change is globally altering our environment with noticeable rising of temperatures, variations of precipitation regimes, and increasing frequency and intensity of extreme weather events (Gobiet et al, 2014; United Nations Environment Programme, 2021; Yoccoz, Delestrade, & Loison, 2010)
From the linear regression computed for 77,761,233 pixels across Switzerland over the 35 years, more than 23% of the normalized difference water index (NDWI) pixels have a significant trend at the 95% confidence level (Figure 5b)
We showed that NDWI time-series extracted from 35 years of Landsat data can be used to monitor vegetation canopy water content at different spatial and temporal scales
Summary
Climate change is globally altering our environment with noticeable rising of temperatures, variations of precipitation regimes, and increasing frequency and intensity of extreme weather events (Gobiet et al, 2014; United Nations Environment Programme, 2021; Yoccoz, Delestrade, & Loison, 2010). These changes have significant impacts on the physical environment exemplified by reduction of snow cover (Schmucki, Marty, Fierz, Weingartner, & Lehning, 2017; Giuliani, et al 2020; Poussin et al, 2019), glaciers receding (Fischer, Fickert, Schwaizer, Patzelt, & Groß, 2019; Zemp, Paul, Hoelzle, Haeberli, & Orlove et al, 2008), soil drying or increased drought frequency (Jiao, Wang, & McCabe, 2021; Magno et al, 2018). Combined with summer high temperatures, dry ness conditions can lead to drought that can have negative impacts on water resources, vegetation or agriculture affecting many water- and land-related ecosystem services (Brun et al, 2020; Mooney et al, 2009; Nolan et al, 2018; Zhou et al, 2017)
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