Abstract
Recent studies have shown that hydro-climatic extremes have increased significantly in number and intensity in the last decades. In the Northern Hemisphere such events were often associated with long lasting persistent weather patterns. In 2018, hot and dry conditions prevailed for several months over Central Europe leading to record-breaking temperatures and severe harvest losses. The underlying circulation processes are still not fully understood and there is a need for improved methodologies to detect and quantify persistent weather conditions. Here, we propose a new method to detect, compare and quantify persistence through atmosphere similarity patterns by applying established image recognition methods to day to day atmospheric fields. We find that persistent weather patterns have increased in number and intensity over the last decades in Northern Hemisphere mid-latitude summer, link this to hydro-climatic risks and evaluate the extreme summers of 2010 (Russian heat wave) and of 2018 (European drought). We further evaluate the ability of climate models to reproduce long-term trend patterns of weather persistence and the result is a notable discrepancy to observed developments.
Highlights
Recent studies have shown that hydro-climatic extremes have increased significantly in number and intensity in the last decades
Applying the new weather persistence index (WPI) to global atmosphere fields we want to answer the following research questions: (1) Trends: Are there signs of long-term changes of regional weather persistence in Northern Hemisphere (NH) summer? (2) Anomalies: Is there a signature of extreme years in weather persistence? (3) Linkage: Which relationship exists to other meteorological quantities? (4) Events: Is there a connection between hydro-climatic extreme events and persisting weather patterns? we are concerned with the crucial question, (5) whether the ability to capture persistence could be a necessary criterion for evaluating the performance of the global climate models (GCMs) simulations to adequately project future weather extremes
Our study time period is 1981–2019 and the observed atmospheric data used are taken from the ECMWF Reanalysis 5th Generation (ERA5)[20]
Summary
Recent studies have shown that hydro-climatic extremes have increased significantly in number and intensity in the last decades. We find that persistent weather patterns have increased in number and intensity over the last decades in Northern Hemisphere mid-latitude summer, link this to hydro-climatic risks and evaluate the extreme summers of 2010 (Russian heat wave) and of 2018 (European drought). Hydro-climatic extremes such as heat waves, droughts and floods[16] can be examined from a different perspective, taking the similarity of weather patterns as a predictor for actual meteorological conditions near the Earth’s surface. Such a predictor would be a useful criterion to validate the outcome of climate m odels[35]. This is critical in climate scenario simulations: If missed or spatially dislocated, such underlying dynamical features cannot be introduced by downscaling[26] or bias adjustment approaches[22] afterwards
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