Response of the European Hydrological Cycle and Soil Moisture to Rising Atmospheric CO2
Anthropogenic activities have significantly altered the climate since the pre-industrial period, resulting in an approximate 1.3°C increase in global near-surface temperatures. These temperature changes cause, among other things, a response of the hydrological cycle and soil moisture. This thesis presents a comprehensive analysis of the European hydrological cycle and associated soil moisture changes due to anthropogenic CO2 emissions using a Single-Model Initial-condition Large Ensemble of 100 simulations performed with the Kiel Climate Model. In these simulations the atmospheric CO2 concentration increases by 1% per year for 140 years. The first study shows a significant reduction in summer and fall soil moisture, reaching up to 31% less relative to its reference state, across most of Central Europe and the Mediterranean. This loss in soil moisture is primarily driven by a reduction in precipitation, which in turn is partly associated with a northward shift in the summer storm track. The second study uses the Time of Emergence (ToE) metric to detect the signal of climate change from the natural variability of a pre-industrial climate state for European summer trends. The ToEs reveal an early emergence of near-surface temperature trends across all of Europe. In contrast, precipitation trends remain undetectable, while soil moisture trends become detectable in some regions. A statistical analysis shows that future summers are significantly different from pre-industrial summers in all analyzed quantities. Additionally, extremely dry summers (99th percentile) are projected to become more extreme, relative to their mean climate, in the future. Overall, this thesis provides insights into projected changes in the European hydrological cycle and soil moisture under a warming climate using a Single-Model Initial-condition Large Ensemble of simulations.
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