A new dynamical systems perspective on atmospheric predictability: Eastern Mediterranean weather regimes as a case study

Hochman, Assaf; Alpert, Pinhas; Harpaz, Tzvi; Saaroni, Hadas; Messori, Gabriele

doi:10.1126/sciadv.aau0936

Cited by 67 publications

(81 citation statements)

References 43 publications

(75 reference statements)

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“…atmospheric rivers driving storm surges and river flooding); iv) spatio-temporal shifts in the distribution of multi-hazards and v) the application of multivariate extreme value statistics (e.g. and dynamical systems theory (De Luca et al, 2019b;Faranda et al, 2017bFaranda et al, , 2017aHochman et al, 2019;Lucarini et al, 2016Lucarini et al, , 2012Messori et al, 2017;Rodrigues et al, 2018) to climate projections (Faranda et al, 2019). Such research efforts could also focus on different spatial scales, from cities, to countries, continents and global areas.…”

Section: Concluding Remarks About Multi-hazardsmentioning

confidence: 99%

Concurrent Hydroclimatic Hazards from Catchment to Global Scales

Luca¹

2020

Preprint

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Interactions between multiple hazards can cause socio-economic damages that exceed those expected by the individual hazard components. Over the past decade, the multi-hazards paradigm has emerged to the extent that the Sendai Framework for Disaster Risk Reduction 2015-2030 advocated a multi-hazard approach. This thesis examines three types of concurrent hydroclimatic hazards that can occur at catchment to global scales. The first multi-hazard is the link between multi-basin flooding (MBF) and extra-tropical cyclones (ETCs) over Great Britain during the period 1975-2014. Results show that during the most geographically widespread MBF episode, up to 108 river catchments (or ~46% of the study area) recorded a peak flow annual maximum within a 16-day window. Most extreme MBF episodes were linked to cyclonic Lamb Weather Types (LWTs), atmospheric rivers and very severe gales. These episodes were associated with significant socio-economic impacts due to widespread flooding. The second hazard was observed (1971-2000) and projected (2011-2100) LWTs, whose seasonal frequency and persistence are associated with multi-hazards over the British Isles. Daily sea-level-pressure data from two reanalyses products, one subjective weather pattern catalogue and an ensemble of 10 Atmosphere-Ocean General Circulation Models (AOGCMs) were used to compute LWTs. Results showed that the AOGCMs are overall able to reproduce historical weather pattern persistence, which, along with annual frequency, is projected to significantly increase anticyclonic and decrease cyclonic LWTs, in summer and autumn respectively. This implies a higher risk of drought, heatwaves and air pollution events in summer but reduced likelihood of flooding and severe gales in autumn by the end of the 21st century. By 2100, the AOGCMs suggest an increased risk of concurrent flood-wind hazards during winter. In summer, the strength of the nocturnal Urban Heat Island (UHI) of London is expected to intensify by the end of the century, contributing to higher chances of combined heatwave-air pollution events. The third type of multi-hazard investigated was the spatio-temporal concurrence of global wet and dry hydrological extremes, during the 1950-2014 period. The analysis was conducted using the monthly self-calibrated Palmer Drought Severity Index based on the Penman-Monteith model (sc_PDSI_pm). Results showed that the land area impacted by extreme dry and wet-dry events significantly increased over the observational period. The most geographically widespread wet-dry event covered a total area of 21 million km2 (or 14% of the global land area) with documented flood and drought impacts over diverse regions. Two new metrics were developed to provide more insight into the combined wet and dry hazards: the wet-dry (WD) ratio and the extreme transitions (ET) time interval. The former quantifies the predominance of wet or dry extremes over a given area, whereas the ET measures the average separation time between the opposite extremes (i.e. between wet to dry or dry to wet transitions). The WD-ratio reveals a predominance of wet over dry extremes in the USA, northern and southern south America, northern Europe, north Africa, western China and most of Australia. The ET median for wet to dry is ~27 months, and 21 months for dry to wet. Global correlations between wet-dry hydrological extremes and El Niño Southern Oscillation (ENSO), Pacific Decadal Oscillation (PDO) and American Multidecadal Oscillation (AMO) were also investigated. ENSO and PDO showed similar correlation patterns, with the former significantly impacting a larger area. On the other hand, the AMO showed an almost inverse spatial correlation pattern, with an overall larger area impacted. The findings presented in this thesis could be informative for emergency responders and relief agencies, disaster risk reduction practitioners, and (re)insurance companies. For instance, multi-basin flooding co-occurring with ETCs could overwhelm emergency response that depends on support from neighbouring regions that are similarly affected. Economic damages could exceed those insured by households and businesses. Projected rises in nocturnal UHI intensity in London could exacerbate heat-stress and, when combined with episodes of poor air quality, increase the likelihood of health problems amongst vulnerable groups. Furthermore, concurrent wet and dry hydrological extremes could be significant for organizations with global assets or sensitive supply chains, and the hydropower, agricultural and transport sectors. Global maps generated of major wet-dry events and the WD-ratio could also be integrated into a seasonal forecasting product, to help stakeholders in hedging the risk. Key opportunities for further research on multi-hazards are future hydroclimatic projections in the light of anthropogenic climate change and the application of new statistical techniques that could help in discerning the driving physical processes.

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Section: Concluding Remarks About Multi-hazardsmentioning

confidence: 99%

Concurrent Hydroclimatic Hazards from Catchment to Global Scales

Luca¹

2020

Preprint

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“…To estimate the local dimension we leverage the Freitas-Freitas-Todd theorem (Freitas et al, 2010), modified by Lucarini et al (2012), which characterises the system's recurrences around the state of interest ζ. d is a proxy for the number of active degrees of freedom of the system about ζ, and can also be related to the state's intrinsic predictability (Messori et al, 2017;Hochman et al, 2019a). Intuitively, a state with a low local dimension will afford a better predictability than one with a higher d.…”

Section: Dynamical Systems Metricsmentioning

confidence: 99%

A Dynamical Systems Characterisation of Atmospheric Jet Regimes

Messori¹,

Harnik²,

Madonna³

et al. 2020

Preprint

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Abstract. Atmospheric jet streams are typically separated into primarily eddy-driven, or polar-front jets and primarily thermally-driven, or "subtropical" jets. Some regions also display merged jets, resulting from the (quasi) co-location of the regions of eddy generation with the subtropical jet. The different locations and driving mechanisms of these jets issue from very different underlying mechanisms, and result in very different jet characteristics. Here, we link our understanding of the dynamical jet maintenance mechanisms, mostly issuing from conceptual or idealised models, to the phenomena observed in reanalysis data. We specifically focus on developing a unitary analysis framework, grounded in dynamical systems theory, which may be applied to both idealised model and reanalysis data, and allow for direct intercomparison. Our results provide a proof-of-concept for using dynamical systems indicators to diagnose jet regimes in a versatile, conceptually intuitive and computationally efficient fashion.

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“…In this study, we use a dynamical systems approach to compute two metrics: θ −1 and α. θ −1 , which we term persistence, is very intuitively a measure of the average residence time of the system around a state of interest. Hence, the higher the value of θ −1 , the more likely it is that the preceding and future states of the system will resemble the current state over relatively long timescales (Faranda et al, 2017b;Messori et al, 2017;Hochman et al, 2019). α, which we term co-recurrence ratio, is a measure of the dynamical coupling between two variables.…”

Section: Dynamical Systems Metricsmentioning

confidence: 99%

Compound Hot-Dry and Cold-Wet Dynamical Extremes Over the Mediterranean

Luca¹,

Messori²,

Faranda³

et al. 2020

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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 and future disaster risk reduction measures. Here, we apply a novel method to study compound events based on dynamical systems theory and analyse compound temperature and precipitation anomalies over the MED from 1979 to 2018. The dynamical systems analysis measures the strength of the coupling between different atmospheric variables over the MED. Further, we consider compound hot-dry days in summer and cold-wet days in winter. Our results show that these hot-dry and cold-wet compound days are associated with maxima in the temperature–precipitation coupling parameter of the dynamical systems analysis. This indicates that there is a strong interaction between temperature and precipitation during compound events. In summer, we find a significant upward trend in the coupling between temperature and precipitation over 1979–2018, which is likely driven by a stronger coupling during hot and dry days. Thermodynamic processes associated with long-term MED warming can best explain the trend. No such trend is found for wintertime cold-wet compound events. Our findings suggest that long-term warming strengthens the coupling of temperature and precipitation which intensifies hot-dry compound events.

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A new dynamical systems perspective on atmospheric predictability: Eastern Mediterranean weather regimes as a case study

Cited by 67 publications

References 43 publications

Concurrent Hydroclimatic Hazards from Catchment to Global Scales

Concurrent Hydroclimatic Hazards from Catchment to Global Scales

A Dynamical Systems Characterisation of Atmospheric Jet Regimes

Compound Hot-Dry and Cold-Wet Dynamical Extremes Over the Mediterranean

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