A seasonal weather perspective on forest vitality, vapor pressure deficit, and Greenland melt in a warming climate

• Main Author: Hermann, Mauro
• Other Authors: Wernli, Heini, Röthlisberger, Matthias, Brönnimann, Stefan
• Format: Doctoral or Postdoctoral Thesis
• Language: English
• Published: ETH Zurich 2023
• Subjects: Seasonal variability; atmospheric dynamics; forest greenness; vapor pressure deficit (VPD); Greenland Ice Sheet; info:eu-repo/classification/ddc/550; Earth sciences; Greenland; Ice Sheet
• Online Access: https://hdl.handle.net/20.500.11850/638327; https://doi.org/10.3929/ethz-b-000638327

A wide range of meteorological and climatological phenomena shape atmospheric variability on different timescales. For example, convection in thunderstorms leads to intense precipitation within minutes, while stationary anticyclones often cause multi-day heat waves. In contrast, only few atmospheric phenomena operate on the seasonal timescale, where climate variability has a very strong impact on many natural and socioeconomic systems. Moreover, seasonal climate variability is relatively more affected by global warming than shorter-term variability, making these systems particularly vulnerable to ongoing global warming. Therefore, the aim of this thesis is to improve our understanding of seasonal climate variability, which is crucial for the development of timely adaptation and preparedness strategies. To achieve this goal, our approach adopts a “weather perspective”, i.e., we investigate how shorter-term atmospheric variability aggregates to form seasonal anomalies and extremes. We also focus on three selected components of the climate system that show remarkable sensitivity to seasonal variability. First, we examine the meteorological precursors of low forest vitality events in Europe during summer (June-August; JJA) using satellite observations of forest greenness. Although these events are indicative of the observed drought-related forest dieback, they have not been systematically assessed from the weather perspective yet. Second, we examine extremely high vapor pressure deficit (VPD) in JJA, which is a major contributor to plant water stress and thus crop failure and wildfire risk. Extreme seasonal VPD can be caused by a combination of air temperature anomalies (T’) and humidity anomalies (q’), which we investigate for the first time over the northern mid-latitudes. Finally, we examine the increase in summer melt of the Greenland Ice Sheet (GrIS) over the 21st century, which is expected to contribute significantly to global sea-level rise. In particular, we quantify the role of melt expansion and ...