Dim Coumou

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

36.84
 · 
Associate Professor

About

123
Publications
47,210
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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 (123)
Article
Full-text available
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
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
Full-text available
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
Full-text available
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...
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
Full-text available
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...
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
Full-text available
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
Full-text available
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
Full-text available
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
Full-text available
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
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
Full-text available
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
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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
Full-text available
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
Full-text available
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
Full-text available
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...
Article
Full-text available
Several recent northern hemisphere summer extremes have been linked to persistent high-amplitude wave patterns (e.g. heat waves in Europe 2003, Russia 2010 and in the US 2011, Floods in Pakistan 2010 and Europe 2013). Recently quasi-resonant amplification (QRA) was proposed as a mechanism that, when certain dynamical conditions are fulfilled, can l...
Article
Variability in the stratospheric polar vortex (SPV) can influence the tropospheric circulation and thereby winter weather. Early predictions of extreme SPV states are thus important to improve forecasts of winter weather including cold spells. However, dynamical models are usually restricted in lead-time because they poorly capture low-frequency pr...
Article
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This paper synthesizes what is known about the physical and biophysical impacts of climate change and their consequences for societies and development under different levels of global warming in Latin America and the Caribbean (LAC). Projections show increasing mean temperatures by up to 4.5 C compared to pre-industrial by the end of this century a...
Article
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This paper synthesizes what is known about the physical and biophysical impacts of climate change and their consequences for societies and development under different levels of global warming in Central Asia. Projections show mean temperatures increasing by up to 6.5 °C compared to pre-industrial by the end of this century across the region. Associ...
Article
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The repercussions of climate change will be felt in various ways throughout both natural and human systems in Sub-Saharan Africa. Climate change projections for this region point to a warming trend, particularly in the inland subtropics; frequent occurrence of extreme heat events; increasing aridity; and changes in rainfall---with a particularly pr...
Article
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This paper reviews the current knowledge of climatic risks and impacts in South Asia associated with anthropogenic warming levels of 1.5–4 °C above pre-industrial values in the twenty-first century. It is based on the World Bank Report “Turn Down the Heat, Climate Extremes, Regional Impacts and the Case for Resilience” (2013b) . Many of the climate...
Article
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The Middle East and North Africa (MENA) region emerges as one of the hot spots for worsening extreme heat, drought and aridity conditions under climate change. A synthesis of peer-reviewed literature from 2010 to date and own modeling work on biophysical impacts of climate change on selected sectors shows that the region is highly affected by prese...
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, jet streams, storm tracks and planetary waves. Associated impacts cover a b...
Chapter
Full-text available
Changes in atmospheric circulation can strongly alter the frequency and/or magnitude of high-impact extreme weather events. Here we address the link between circulation changes and the occurrence of long-lasting heat waves in the Northern Hemisphere summer. We show that boreal summer circulation has seen pronounced changes in circulation over the l...
Article
Full-text available
Scientific Reports 7 : Article number: 45242; 10.1038/srep45242 published online: 27 March 2017 ; updated: 26 May 2017 . This Article contains an error in Figure 1a, where the y-axis ‘Temperature (K)’ is incorrectly labelled as ‘Temperature (°C)’.
Article
Slow-moving planetary waves of high amplitudes are often associated with persistent surface weather conditions. This persistence can lead to extreme weather events with potentially serious implications for society and nature. Quasi-resonant amplification of planetary waves (QRA) has been proposed as a mechanism to generate high-amplitude hemisphere...
Article
Full-text available
Persistent episodes of extreme weather in the Northern Hemisphere summer have been shown to be associated with the presence of high-amplitude quasi-stationary atmospheric Rossby waves within a particular wavelength range (zonal wavenumber 6?8). The underlying mechanistic relationship involves the phenomenon of quasi-resonant amplification (QRA) of...
Article
Full-text available
The polar and subtropical jet streams are strong upper-level winds with a crucial influence on weather throughout the Northern Hemisphere midlatitudes. In particular, the polar jet is located between cold arctic air to the north and warmer subtropical air to the south. Strongly meandering states therefore often lead to extreme surface weather. Som...
Preprint
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, which is a Statistical Dynamical Atmosphere Model (SDAM) and includes radiative transfer and cloud modules (Coumou, 2011;...
Article
Full-text available
Strong waves in the mid-latitude circulation have been linked to extreme surface weather and thus changes in waviness could have serious consequences for society. Several theories have been proposed which could alter waviness, including tropical sea surface temperature anomalies or rapid climate change in the Arctic. However, so far it remains uncl...
Article
Full-text available
The polar and subtropical jet streams are strong upper-level winds with a crucial influence on weather throughout the Northern Hemisphere mid-latitudes. In particular, the polar jet is located between cold Arctic air to the North and warmer sub-tropical air to the South. Strongly meandering states therefore often lead to extreme surface weather. So...
Article
Full-text available
In boreal spring-to-autumn (May-to-September) 2012 and 2013, the Northern Hemisphere (NH) has experienced a large number of severe midlatitude regional weather extremes. Here we show that a considerable part of these extremes were accompanied by highly magnified quasistationary midlatitude planetary waves with zonal wave numbers m = 6, 7, and 8. We...