Dim Coumou

Dim Coumou
Potsdam Institute for Climate Impact Research | PIK · Earth System Analysis - Research Domain I

Associate Professor

About

141
Publications
76,602
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Introduction
Coumou is a climate scientist with a PhD in Natural Sciences from ETH-Zurich (2008) for which he received the ETH-medal for outstanding thesis. He is Associate Professor ‘Extreme Weather & Climate Change’ at VU Amsterdam and group leader at Potsdam Institute for Climate Impact Research. He studies how global warming affects the number and intensity of extreme weather (heat waves, extreme rain, droughts) using climate models, causal inference, machine learning etc. He authored over 60 papers.

Publications

Publications (141)
Article
Full-text available
In boreal summer, circumglobal Rossby waves can promote stagnating weather systems that favor extreme events like heat waves or droughts. Recent work showed that amplified Rossby wavenumber 5 and 7 show phase-locking behavior which can trigger simultaneous warm anomalies in different breadbasket regions in the Northern Hemisphere. These types of wa...
Article
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Persistent heat extremes can have severe impacts on ecosystems and societies, including excess mortality, wildfires, and harvest failures. Here we identify Europe as a heatwave hotspot, exhibiting upward trends that are three-to-four times faster compared to the rest of the northern midlatitudes over the past 42 years. This accelerated trend is lin...
Preprint
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The Last Interglacial (LIG; ca. 125 ka) is a period of interest for climate research as it is the most recent period of the Earth’s history when the boreal climate was warmer than at present. Previous research, based on models and geological evidence, suggests that the LIG may have featured enhanced patterns of ocean storminess, but this remains ho...
Article
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Heatwaves can have devastating impact on society and reliable early warnings at several weeks lead time are needed. Previous studies showed that north-Pacific sea surface temperatures (SST) can provide long-lead predictability for eastern US temperature, mediated by an atmospheric Rossby wave. The exact mechanisms, however, are not well understood....
Article
Reliable sub-seasonal forecasts of high summer temperatures would be very valuable for society. Although state-of-the-art numerical weather prediction (NWP) models have become much better in representing the relevant sources of predictability like land- and sea-surface states, the sub-seasonal potential is not fully realized. Complexities arise bec...
Preprint
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Towards the end of June 2021, temperature records were broken by several degrees Celsius in several cities in the Pacific northwest areas of the U.S. and Canada, leading to spikes in sudden deaths, and sharp increases in hospital visits for heat-related illnesses and emergency calls. Here we present a multi-model, multi-method attribution analysis...
Article
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Summer 2010 saw two simultaneous extremes linked by an atmospheric wave train: a record-breaking heatwave in Russia and severe floods in Pakistan. Here, we study this wave event using a large ensemble climate model experiment. First, we show that the circulation in 2010 reflected a recurrent wave train connecting the heatwave and flooding events. S...
Article
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Over the last decade, the world warmed by 0.25 °C, in-line with the roughly linear trend since the 1970s. Here we present updated analyses showing that this seemingly small shift has led to the emergence of heat extremes that would be virtually impossible without anthropogenic global warming. Also, record rainfall extremes have continued to increas...
Conference Paper
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Here, we examine the impacts of significant atmospheric circulation changes at seasonal scales on European temperature and precipitation and disentangle the thermodynamical from the dynamical contributions, under increasing CO2 concentrations. We use a very high resolution fully-coupled global climate model (CM2.6 GFDL), to document significant cha...
Preprint
Full-text available
In boreal summer, circumglobal Rossby waves can promote stagnating weather systems that favor extreme events like heatwaves or droughts. Recent work highlighted the risks associated with amplified Rossby wavenumber 5 and 7 in triggering simultaneous warm anomalies in specific agricultural breadbaskets in the Northern Hemisphere. These type of wave...
Preprint
Full-text available
The mechanisms leading to the occurrence of extreme weather and climate events are varied and complex. They generally encompass a combination of dynamical and thermodynamical processes, as well as drivers external to the climate system, such as anthropogenic greenhouse gas emissions and land-use change. Here we present the ExtremeX multi-model inte...
Article
Persistent hot-dry or cold-wet summer weather can have significant impacts on agriculture, health and the environment. For North-Western Europe, these weather regimes are typically linked to, respectively, blocked or zonal jetstream states. The fundamental dynamics underlying these circulation states are still poorly understood. Edward Lorenz postu...
Article
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Tropical convective activity represents a source of predictability for mid-latitude weather in the Northern Hemisphere. In winter, the El Niño–Southern Oscillation (ENSO) is the dominant source of predictability in the tropics and extratropics, but its role in summer is much less pronounced and the exact teleconnection pathways are not well underst...
Article
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Extreme summer temperatures can cause severe societal impacts. Early warnings can aid societal preparedness, but reliable forecasts for extreme temperatures at subseasonal-to-seasonal (S2S) timescales are still missing. Earlier work showed that specific sea surface temperature (SST) patterns over the northern Pacific are precursors of high temperat...
Article
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This study investigates the sub-synoptic scale circulation aspects associated with the extreme rainfall event occurred over the North Indian state of Uttarakhand located in the western Himalayas (WH) during the 15–18 June 2013 period. A diagnosis based on hourly ERA5 reanalyzed circulation products archived on finer grids reveals that sustenance of...
Preprint
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Extreme summer weather often has devastating impacts on society when it lasts for many days. Stalling cyclones can lead to flooding and persistent hot-dry conditions can lead to health impacts and harvest losses. Global warming weakens the hemispheric-wide circulation in boreal summer, which has been shown in both observations and models using mult...
Article
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The Mediterranean (MED) Basin is a climate change hotspot that has seen drying and a pronounced increase in heatwaves over the last century. At the same time, it is experiencing increased heavy precipitation during wintertime cold spells. Understanding and quantifying the risks from compound events over the MED is paramount for present and future d...
Book
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The report assesses economic growth and development risks and opportunities for African countries in two scenarios of future climate changes: a low scenario that until mid-century is consistent with the Paris Agreement (well below 2 ̊C, pursue 1.5°C) and a high-warming scenario (2 ̊C by 2050, exceeding 4 ̊C by 2100). It highlights the risks to whic...
Article
The succession of European surface weather patterns has limited predictability because disturbances quickly transfer to the large scale flow. Some aggregated statistic however, like the average temperature exceeding a threshold, can have extended predictability when adequate spatial scales, temporal scales and thresholds are chosen. This study benc...
Preprint
Full-text available
Abstract. Tropical convective activity represents a source of predictability for mid-latitude weather in the Northern Hemisphere. In winter, the El Niño–Southern Oscillation (ENSO) is the dominant source of predictability in the tropics and extra-tropics, but its role in summer is much less pronounced and the exact teleconnection pathways are not w...
Preprint
Full-text available
Abstract. The Mediterranean (MED) basin is a climate change hot-spot that has seen drying and a pronounced increase in heatwaves over the last century. At the same time, it is experiencing increasing heavy precipitation during wintertime cold spells. Understanding and quantifying the risks from compound events over the MED is paramount for present...
Article
Full-text available
The alternation of active and break phases in Indian summer monsoon (ISM) rainfall at intraseasonal timescales characterizes each ISM season. Both tropical and mid-latitude drivers influence this intraseasonal ISM variability. The circumglobal teleconnection observed in boreal summer drives intraseasonal variability across the mid-latitudes, and a...
Article
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In an interconnected world, simultaneous extreme weather events in distant regions could potentially impose high-end risks for societies1,2. In the mid-latitudes, circumglobal Rossby waves are associated with a strongly meandering jet stream and might cause simultaneous heatwaves and floods across the northern hemisphere3–6. For example, in the sum...
Article
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p>The heart of the scientific enterprise is a rational effort to understand the causes behind the phenomena we observe. In large-scale complex dynamical systems such as the Earth system, real experiments are rarely feasible. However, a rapidly increasing amount of observational and simulated data opens up the use of novel data-driven causal methods...
Article
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The Arctic has warmed more than twice as fast as the global average since the late twentieth century, a phenomenon known as Arctic amplification (AA). Recently, there have been considerable advances in understanding the physical contributions to AA, and progress has been made in understanding the mechanisms that link it to midlatitude weather varia...
Article
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The last extended time period when climate may have been warmer than today was during the Last Interglacial (LIG; ca. 129 to 120 thousand years ago). However, a global view of LIG precipitation is lacking. Here, seven new LIG climate models are compared to the first global database of proxies for LIG precipitation. In this way, models are assessed...
Article
The Arctic has warmed more than twice as fast as the global average since the late 20th century, a phenomenon known as Arctic amplification (AA). Recently, there have been significant advances in understanding the physical contributions to AA and progress has been made in understanding the mechanisms linking AA to mid-latitude weather variability....
Article
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Anomalous interactions between the Indian summer monsoon (ISM) circulation and subtropical westerlies are known to trigger breaks in the ISM on subseasonal time-scales, characterised by a pattern of suppressed rainfall over central-north India, and enhanced rainfall over the foothills of the central–eastern Himalayas (CEH). An intriguing feature du...
Article
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Heat and rainfall extremes have intensified over the past few decades and this trend is projected to continue with future global warming1–3. A long persistence of extreme events often leads to societal impacts with warm-and-dry conditions severely affecting agriculture and consecutive days of heavy rainfall leading to flooding. Here we report syste...
Chapter
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This chapter surveys how the state of knowledge about the physical processes that cause extreme heat and the societal factors that determine its impacts can be used to better predict these aspects of future climate change. Covering global projections; event attribu­tion; atmospheric dynamics; regional and local effects; and impacts on health, agric...
Article
Full-text available
The alternation of active and break phases in the Indian summer monsoon (ISM) rainfall at sub-seasonal timescales characterizes each ISM season. Tropical and mid-latitude drivers influence this sub-seasonal ISM variability. The circumglobal teleconnection observed in boreal summer drives sub-seasonal variability across the mid-latitudes and a two-w...
Article
Skillful forecasts of the Indian summer monsoon rainfall (ISMR) at long lead times (4–5 months in advance) pose great challenges due to strong internal variability of the monsoon system and nonstationarity of climatic drivers. Here, we use an advanced causal discovery algorithm coupled with a response-guided detection step to detect low-frequency,...
Article
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Summer weather extremes are often associated with high‐amplitude atmospheric planetary waves (Petoukhov et al., 2013). Such conditions lead to stationary weather patterns, triggering heat waves and sometimes prolonged intense rainfall. These wave events, referred to as periods of Quasi‐Resonant Amplification (QRA), are relatively rare though and he...
Article
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The succession of the July 2018 extreme flood and heat wave in Japan, occurring only a week from each other, follows the unique lifecycle of the East Asian summer monsoon (EASM). The processes leading these opposite extreme events to occur so closely with each other involve distinct subseasonal features of the EASM lifecycle and the marked tropics-...
Article
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The summer of 2018 witnessed a number of extreme weather events such as heatwaves in North America, Western Europe and the Caspian Sea region, and rainfall extremes in South-East Europe and Japan that occurred near-simultaneously. Here we show that some of these extremes were connected by an amplified hemisphere-wide wavenumber 7 circulation patter...
Conference Paper
Full-text available
North Atlantic oceanic and atmospheric variability is central in determining the behavior of surface climate and hence the occurrence of extremes over the Northern Hemisphere, which in turn have huge impacts on societies, economies and environment. The aim of this study is to gain further insight on the evolution of SST and atmospheric circulation...
Article
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The Indian Summer Monsoon (ISM) is characterized by alternating active (wet) and break (dry) phases operating at sub-seasonal timescales, and various studies advocate tropical and mid-latitude teleconnection drivers influence the sub-seasonal ISM rainfall variability. One such driver is the circumglobal teleconnection pattern, which is commonly obs...
Article
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The discipline of seasonal climate prediction began as an exercise in simple statistical techniques. However, today the large government forecast centers almost exclusively rely on complex fully coupled dynamical forecast systems for their subseasonal to seasonal (S2S) predictions while statistical techniques are mostly neglected and those techniqu...
Article
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Climate and weather conditions in the mid-latitudes are strongly driven by the large-scale atmosphere circulation. Observational data indicate that important components of the large-scale circulation have changed in recent decades, including the strength and the width of the Hadley cell, jets, storm tracks and planetary waves. Here, we use a new st...
Article
Climate change alters the hydrological cycle, which is expected to increase the risk of heavy rainfall events and prolonged droughts. Sparse rainfall data, however, have made it difficult to answer the question of whether robust changes can already be seen in the short observational time period. Here we use a comprehensive statistical tool to quant...
Article
Full-text available
Accelerated warming in the Arctic, as compared to the rest of the globe, might have profound impacts on mid-latitude weather. Most studies analyzing Arctic links to mid-latitude weather focused on winter, yet recent summers have seen strong reductions in sea-ice extent and snow cover, a weakened equator-to-pole thermal gradient and associated weake...
Article
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Atmospheric dynamics: Polar stratospheric influence on mid-latitude cold extremes Cold spells in the Northern Hemisphere mid-latitudes are influenced by the stratospheric polar vortex in two different ways. Marlene Kretschmer from the Potsdam Institute for Climate Impact Research, Germany, and collaborators use cluster analysis to show there are tw...
Preprint
The summer of 2018 witnessed a number of extreme weather events such as heatwaves in North America, Western Europe and the Caspian Sea region and rainfall extremes in South-East Europe and Japan that occurred near-simultaneously. Here we show that these extremes were connected by an amplified hemisphere-wide wavenumber 7 circulation pattern. We sho...
Article
Recent studies indicate that the tropical belt has been expanding during recent decades, which can significantly influence precipitation in subtropical climates. Often the location of the tropical border is identified using the Hadley cell edge (HCE) or the subtropical jet stream (STJ), but most studies concentrated on the zonal-mean state, thereby...
Article
Full-text available
Persistent episodes of extreme weather in the Northern Hemisphere summer have been associated with high-amplitude quasi-stationary atmospheric Rossby waves, with zonal wave numbers 6 to 8 resulting from the phenomenon of quasi-resonant amplification (QRA). A fingerprint for the occurrence of QRA can be defined in terms of the zonally averaged surfa...
Article
Full-text available
In May-June 2016 the Canadian Province of Alberta suffered one of the most devastating wildfires in its history. Here we show that in mid-April to early May 2016 the large-scale circulation in the mid- and high troposphere of the middle and sub-polar latitudes of the northern hemisphere featured a persistent high-amplitude planetary wave structure...
Article
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Extreme weather events such as heat waves and floods are damaging to society and their contribution to future climate impacts is expected to be large. Such extremes are often related to persistent local weather conditions. Weather persistence is linked to sea surface temperatures, soil-moisture (especially in summer) and large-scale circulation pat...
Article
Full-text available
Climate and weather conditions in the mid-latitudes are strongly driven by the large-scale atmosphere circulation. Observational data indicates that important components of the large-scale circulation have changed in recent decades including the strength of the Hadley cell, jets, storm tracks and planetary waves. Here, we use a statistical-dynamic...
Article
Full-text available
GOTHAM International Summer School on Global Teleconnections in the Earth’s Climate System – Processes, Modelling and Advanced Analysis Methods; Potsdam, Germany, 18–22 September 2017
Poster
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Changes in the hydrological cycle have large consequences for society. In particular, precipitation extremes and floods may get worse in a warmer climate. Besides relying on global climate models forced with greenhouse scenarios, we may look at past climates to understand how the hydrological cycle may rearrange under warmer conditions. The Last In...
Conference Paper
Full-text available
North Atlantic Oscillation (NAO) is one of the most prominent teleconnection patterns affecting weather and climate over the North Atlantic region and its surrounding continents. Although it is more pronounced in winter, the summer NAO (SNAO) is important as well and it exhibits a different spatial structure. In this study, the main SNAO 'flavors',...
Article
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We present and validate a set of equations for representing the atmosphere's large-scale general circulation in an Earth system model of intermediate complexity (EMIC). These dynamical equations have been implemented in Aeolus 1.0, which is a statistical–dynamical atmosphere model (SDAM) and includes radiative transfer and cloud modules (Coumou et...
Conference Paper
North Atlantic SST variability results from the interaction of atmospheric and oceanic processes. The North Atlantic Oscillation (NAO) drives changes in SST patterns but is also driven by them on certain time-scales. These interactions are not very well understood and might be affected by anthropogenic climate change. Paleo reconstructions indicate...
Article
The European climate is changing under global warming and especially the Mediterranean region has been identified as a hotspot for climate change with climate models projecting a reduction in winter rainfall and a very pronounced increase in summertime heat waves. These trends are already detectable over the historic period. Hence, it is beneficial...
Article
Full-text available
The extratropical stratosphere in boreal winter is characterized by a strong circumpolar westerly jet, confining the coldest temperatures at high latitudes. The jet, referred to as the stratospheric polar vortex, is predominantly zonal and centered around the pole; however, it does exhibit large variability in wind speed and location. Previous stud...