Europe-Atlantic jet caused dipole mode of European climate and increased climatic extremes

2021 ◽  
Author(s):  
Guobao Xu ◽  
Meko Matthew ◽  
Lara Klippel ◽  
Isabel Dorado-Liñán ◽  
Valerie Trouet
Keyword(s):  
Regional Climate ◽  
Ring Width ◽  
Occurrence Rate ◽  
Jet Stream ◽  
Dipole Mode ◽  
Large Variability ◽  
Climatic Extremes ◽  
High Occurrence ◽  
European Climate ◽  
Western Eurasia

<p><strong>The jet stream configuration over the Atlantic Ocean and the European </strong><strong>continent</strong><strong> substantially affects climatic extremes in Western Eurasia by transporting heat and vorticity</strong><strong>. </strong><strong>However, how the Europe-Atlantic jet configuration varies and how it affects European climate on the long time-scales are still unclear. We compiled a network of tree-ring width, blue intensity, and maximum density chronologies from Europe to explore past variability in the summer Europe-Atlantic Jet stream and its influence on regional climate. By combining five regional chronologies, we were able to reconstruct July-August jet stream latitude (JSL) PC2 variability over the past millennium (978-2010 CE) for the Europe-Atlantic domain (30°W to 40°E). Our reconstruction explains 40% of summer JSL PC2 variability over the instrumental period (1948-2010 CE) with strong skill. Our millennial-long reconstruction shows that summer JSL is a relevant driver of the temperature, precipitation, and drought dipoles observed between Northwestern and Southern Europe. Positive summer JSL PC2 values (northward jet position) generally lead to a strengthening of the European summer climate dipole, while negative values (southward jet position) lead to a weak or insignificant dipole mode. Our summer JSL reconstruction shows large variability and a high occurrence rate of extremes over the 20<sup>th</sup> century, as well as 1200-1350 CE Medieval Climate Anomaly (MCA). The high occurrence rate of summer JSL extremes corresponds to periods with increased number of climatic extremes. Our results suggest that the summer JSL contributes to the European climate dipole both in a long-term context and in its extremes. We also reveal that the occurrence rate of summer JSL extremes is double during the 20<sup>th</sup> century compared to other periods, especially for the negative extremes, which might be related to anthropogenic warming. Our results suggest a high occurrence rate of summer JSL extremes during the 20<sup>th</sup> century, leading to more climatic extremes in Europe, as well as a prevailing northward summer JSL position resulting in a weakening climatic dipole.</strong></p>

Using convection-permitting climate models and a high-resolution distributed hydrological model to assess future changes in Alpine flash floods.

2021 ◽  
Author(s):  
Marjanne Zander ◽  
Pety Viguurs ◽  
Frederiek Sperna Weiland ◽  
Albrecht Weerts
Keyword(s):  
High Resolution ◽  
Natural Hazards ◽  
Climate Models ◽  
Flash Flood ◽  
Regional Climate ◽  
Flash Floods ◽  
Flood Frequency ◽  
Climate Dynamics ◽  
Future Climate ◽  
European Climate

<p>Flash Floods are damaging natural hazards which often occur in the European Alps. Precipitation patterns and intensity may change in a future climate affecting their occurrence and magnitude. For impact studies, flash floods can be difficult to simulate due the complex orography and limited extent & duration of the heavy rainfall events which trigger them. The new generation convection-permitting regional climate models improve the intensity and frequency of heavy precipitation (Ban et al., 2021).</p><p>Therefore, this study combines such simulations with high-resolution distributed hydrological modelling to assess changes in flash flood frequency and occurrence over the Alpine terrain. We use the state-of-the-art Unified Model (Berthou et al., 2018) to drive a high-resolution distributed hydrological wflow_sbm model (e.g. Imhoff et al., 2020) covering most of the Alpine mountain range on an hourly resolution. Simulations of the future climate RCP 8.5 for the end-of-century (2096-2105) and current climate (1998-2007) are compared.</p><p>First, the wflow_sbm model was validated by comparing ERA5 driven simulation with streamflow observations (across Rhone, Rhine, Po, Adige and Danube). Second, the wflow_sbm simulation driven by UM simulation of the current climate was compared to a dataset of historical flood occurrences (Paprotny et al., 2018, Earth Syst. Sci. Data) to validate if the model can accurately simulate the location of the flash floods and to determine a suitable threshold for flash flooding. Finally, the future run was used to asses changes in flash flood frequency and occurrence. Results show an increase in flash flood frequency for the Upper Rhine and Adige catchments. For the Rhone the increase was less pronounced. The locations where the flash floods occur did not change much.</p><p>This research is embedded in the EU H2020 project EUCP (EUropean Climate Prediction system) (https://www.eucp-project.eu/), which aims to support climate adaptation and mitigation decisions for the coming decades by developing a regional climate prediction and projection system based on high-resolution climate models for Europe.</p><p> </p><p>N. Ban, E. Brisson, C. Caillaud, E. Coppola, E. Pichelli, S. Sobolowski, …, M.J. Zander (2021): “The first multi-model ensemble of regional climate simulations at the kilometer-scale resolution, Part I: Evaluation of precipitation”, manuscript accepted for publication in Climate Dynamics.</p><p>S. Berthou, E.J. Kendon, S. C. Chan, N. Ban, D. Leutwyler, C. Schär, and G. Fosser, 2018, “Pan-european climate at convection-permitting scale: a model intercomparison study.” Climate Dynamics, pages 1–25, DOI: 10.1007/s00382-018-4114-6</p><p>Imhoff, R.O., W. van Verseveld, B. van Osnabrugge, A.H. Weerts, 2020. “Scaling point-scale pedotransfer functions parameter estimates for seamless large-domain high-resolution distributed hydrological modelling: An example for the Rhine river.” Water Resources Research, 56. Doi: 10.1029/2019WR026807</p><p>Paprotny, D., Morales Napoles, O., & Jonkman, S. N., 2018. "HANZE: a pan-European database of exposure to natural hazards and damaging historical floods since 1870". Earth System Science Data, 10, 565–581, https://doi.org/10.5194/essd-10-565-2018</p>

scholarly journals North American Climate in CMIP5 Experiments. Part I: Evaluation of Historical Simulations of Continental and Regional Climatology

2013 ◽  
Vol 26 (23) ◽  
pp. 9209-9245 ◽  
Author(s):  
Justin Sheffield ◽  
Andrew P. Barrett ◽  
Brian Colle ◽  
D. Nelun Fernando ◽  
Rong Fu ◽  
...  
Keyword(s):  
North American ◽  
Regional Climate ◽  
Arctic Sea Ice ◽  
North American Monsoon ◽  
Multimodel Ensemble ◽  
Western Atlantic ◽  
Large Variability ◽  
The North ◽  
North American Climate ◽  
Hydrological Variables

This is the first part of a three-part paper on North American climate in phase 5 of the Coupled Model Intercomparison Project (CMIP5) that evaluates the historical simulations of continental and regional climatology with a focus on a core set of 17 models. The authors evaluate the models for a set of basic surface climate and hydrological variables and their extremes for the continent. This is supplemented by evaluations for selected regional climate processes relevant to North American climate, including cool season western Atlantic cyclones, the North American monsoon, the U.S. Great Plains low-level jet, and Arctic sea ice. In general, the multimodel ensemble mean represents the observed spatial patterns of basic climate and hydrological variables but with large variability across models and regions in the magnitude and sign of errors. No single model stands out as being particularly better or worse across all analyses, although some models consistently outperform the others for certain variables across most regions and seasons and higher-resolution models tend to perform better for regional processes. The CMIP5 multimodel ensemble shows a slight improvement relative to CMIP3 models in representing basic climate variables, in terms of the mean and spread, although performance has decreased for some models. Improvements in CMIP5 model performance are noticeable for some regional climate processes analyzed, such as the timing of the North American monsoon. The results of this paper have implications for the robustness of future projections of climate and its associated impacts, which are examined in the third part of the paper.

scholarly journals Tree-ring reconstruction of June-July mean temperatures in the northern Daxing’an Mountains, China

2020 ◽  
Vol 47 (1) ◽  
pp. 13-22
Author(s):  
Yangao Jiang ◽  
Yu Wang ◽  
Junhui Zhang ◽  
Shijie Han ◽  
Cassius E.O. Coombs ◽  
...  
Keyword(s):  
Tree Ring ◽  
Southern Oscillation ◽  
Regional Climate ◽  
Ring Width ◽  
Temperature Reconstruction ◽  
Global Scale ◽  
Spatial Correlations ◽  
Regional Study ◽  
Average Value ◽  
Daxing’An Mountains

AbstractIn this study, the mean temperature of June to July was reconstructed for the period of 1880 to 2014 by using the Larix gmelinii tree-ring width data for the Mangui region in the northern Daxing’an Mountains, China. The reconstruction accounts for 43.6% of the variance in the temperature observed from AD 1959–2014. During the last 134 years, there were 17 warm years and 17 cold years, which accounted for 12.7% of the total reconstruction years, respectively. Cold episodes occurred throughout 1887–1898 (average value is 14.2°C), while warm episodes occurred during 1994–2014 (15.9°C). Based on this regional study, the warmer events coincided with dry periods and the colder events were consistent with wet conditions. The spatial correlation analyses between the reconstructed series and gridded temperature data revealed that the regional climatic variations were well captured by this study and the reconstruction represented a regional temperature signal for the northern Daxing’an Mountains. In addition, Multi-taper method spectral analysis revealed the existence of significant periodicities in our reconstruction. Significant spectral peaks were found at 29.7, 10.9, 2.5, and 2.2 years. The significant spatial correlations between our temperature reconstruction and the El Niño–Southern Oscillation (ENSO), Pacific Decadal Oscillation (PDO) and Solar activity suggested that the temperature in the Daxing’an Mountains area indicated both local-regional climate signals and global-scale climate changes.

scholarly journals Vegetation response to the African Humid Period termination in central Cameroon (7° N) – new pollen insight from Lake Mbalang

2009 ◽  
Vol 5 (6) ◽  
pp. 2577-2606 ◽  
Author(s):  
A. Vincens ◽  
G. Buchet ◽  
M. Servant ◽  
Keyword(s):  
Forest Regeneration ◽  
Regional Climate ◽  
Central Africa ◽  
Forest Degradation ◽  
Vegetation Response ◽  
Tropical Africa ◽  
Climatic Extremes ◽  
Study Sites ◽  
The Stability ◽  
Humid Period

Abstract. A new pollen sequence from the Lake Mbalang (7°19' N, 13°44' E, 1110 m a.s.l.) located on the eastern Adamawa plateau, in central Cameroon, is presented in this paper to analyze the Holocene African Humid Period (AHP) termination and related vegetation changes at 7° N in tropical Africa, a region where any data are today available. This sequence, spanning the last 7000 cal. yr BP, shows that the vegetation response to this transitional climatic episode was neither abrupt nor really gradual. Forest degradation in this area is initially registered as early as 6100 cal. yr BP and modern savanna was definitely established at 3000 cal. yr BP and stabilized at 2400 cal. yr BP; but a slight forest regeneration episode is observed between 5200 and 4200 cal. yr BP. Moreover, in this area with modern high rainfall, increasing in the length of the dry season during the AHP termination, from 6100 cal. yr BP onward, has primarily controlled vegetation dynamics and above all the disappearance of a forested environment on the Adamawa plateau. Compared to previous studies undertaken in northern tropical and central Africa, this work clearly shows that the response of vegetation to transitional episodes between climatic extremes such as the AHP termination might be different in timing, mode and amplitude according to the regional climate and hydrology of the study sites, but also according to the stability of vegetation before and during these climatic transitions.

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