Winter hydrometeorological extreme events modulated by large scale atmospheric circulation in southern Ontario

Abstract. Extreme events are widely studied across the world because of their major implications for many aspects of society and especially floods. These events are generally studied in term of precipitation or temperature extreme indices that are often not adapted for regions affected by floods caused by snowmelt. Rain on Snow index has been widely used but it neglects rain only events which are expected to be more frequent in the future. In this study we identified a new winter compound index and assessed how large-scale atmospheric circulation controls the past and future evolution of these events in the Great Lakes region. The future evolution of this index was projected using temperature and precipitation from the Canadian Regional Climate Model Large Ensemble (CRCM5-LE). These climate data were used as input in PRMS hydrological model to simulate the future evolution of high flows in three watersheds in Southern Ontario. We also used five recurrent large-scale atmospheric circulation patterns in northeastern North America and identified how they control the past and future variability of the newly created index and high flows. The results show that daily precipitation higher than 10 mm and temperature higher than 5 °C were a necessary historical condition to produce high flows in these three watersheds. In the historical period, the occurrences of these heavy rain and warm events as well as high flows were associated to two main patterns characterized by high Z500 anomalies centred on eastern Great Lakes (HP) and the Atlantic Ocean (South). These hydrometeorological extreme events will be more frequent in the near future and will still be associated to the same atmospheric patterns. The future evolution of the index will be modulated by the internal variability of the climate system as higher Z500 in the east coast will amplify the increase in the number of events, especially the warm events. The relationship between the extreme weather index and high flows will be modified in the future as the snowpack reduces and rain becomes the main component of high flows generation. This study shows the values of CRCM5-LE dataset to simulate hydrometeorological extreme events in Eastern Canada and to better understand the uncertainties associated to internal variability of climate.

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Winter hydrometeorological extreme events modulated by large-scale atmospheric circulation in southern Ontario

Earth System Dynamics ◽

10.5194/esd-11-301-2020 ◽

2020 ◽

Vol 11 (1) ◽

pp. 301-318 ◽

Cited By ~ 1

Author(s):

Olivier Champagne ◽

Martin Leduc ◽

Paulin Coulibaly ◽

M. Altaf Arain

Keyword(s):

Atmospheric Circulation ◽

Extreme Events ◽

Large Scale ◽

Internal Variability ◽

Southern Ontario ◽

Future Evolution ◽

The Past ◽

The Future ◽

High Flows ◽

Large Scale Atmospheric Circulation

Abstract. Extreme events are widely studied across the world because of their major implications for many aspects of society and especially floods. These events are generally studied in terms of precipitation or temperature extreme indices that are often not adapted for regions affected by floods caused by snowmelt. The rain on snow index has been widely used, but it neglects rain-only events which are expected to be more frequent in the future. In this study, we identified a new winter compound index and assessed how large-scale atmospheric circulation controls the past and future evolution of these events in the Great Lakes region. The future evolution of this index was projected using temperature and precipitation from the Canadian Regional Climate Model large ensemble (CRCM5-LE). These climate data were used as input in Precipitation Runoff Modelling System (PRMS) hydrological model to simulate the future evolution of high flows in three watersheds in southern Ontario. We also used five recurrent large-scale atmospheric circulation patterns in north-eastern North America and identified how they control the past and future variability of the newly created index and high flows. The results show that daily precipitation higher than 10 mm and temperature higher than 5 ∘C were necessary historical conditions to produce high flows in these three watersheds. In the historical period, the occurrences of these heavy rain and warm events as well as high flows were associated with two main patterns characterized by high Z500 anomalies centred on eastern Great Lakes (HP regime) and the Atlantic Ocean (South regime). These hydrometeorological extreme events will still be associated with the same atmospheric patterns in the near future. The future evolution of the index will be modulated by the internal variability of the climate system, as higher Z500 on the east coast will amplify the increase in the number of events, especially the warm events. The relationship between the extreme weather index and high flows will be modified in the future as the snowpack reduces and rain becomes the main component of high-flow generation. This study shows the value of the CRCM5-LE dataset in simulating hydrometeorological extreme events in eastern Canada and better understanding the uncertainties associated with internal variability of climate.

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Do CMIP5 emergent constraints on the large scale atmospheric circulation work to constrain CMIP6 projections?

10.5194/egusphere-egu2020-4001 ◽

2020 ◽

Author(s):

Isla Simpson ◽

Fances Davenport ◽

Abdullah Al Fahad ◽

Flavio Lehner

Keyword(s):

Atmospheric Circulation ◽

Large Scale ◽

Coupled Model ◽

Internal Variability ◽

Stationary Waves ◽

Projected Change ◽

Emergent Constraints ◽

Out Of Sample ◽

Emergent Constraint ◽

Large Scale Atmospheric Circulation

Accurate future projections of the climate system are hindered by a number of sources of uncertainty: forcing uncertainty, internal variability and model structural uncertainty. An ``Emergent constraint'' is a technique that has been devised to reduce projection uncertainties arising from the model structural component. It consists of a statistical relationship (across a model ensemble) between a model&#8217;s representation of some aspect of the present day climate and its future projected climate change. This relationship can then be used to imply the future projected change, given the observed value of that present-day aspect. However, in order for the emergent constraint to be considered robust it must: (a) be accompanied by a physical mechanism and (b) be robust to out-of-sample testing.&#160;In prior Coupled Model Intercomparison Projects (CMIP), in particular CMIP5, a number of emergent constraints on the large scale atmospheric circulation were proposed, with implications for regional hydroclimate change. These include: (1) a relationship between a model&#8217;s climatological jet latitude and its future projected poleward shift in the Southern Hemisphere; (2) a relationship between a model&#8217;s future projected wintertime circulation and hydroclimate change over North America and its climatological representation of stationary waves in the North Pacific; and (3) a relationship between a model&#8217;s future projected precipitation change over California and its representation of the relationship between ENSO and California precipitation. Constraints (2) and (3) actually imply opposite constraints on California precipitation changes for the real world, which speaks to the need for a deeper understanding of these emergent constraints and a comprehensive assessment of their robustness.&#160;While the CMIP6 archive does not represent a true ``out-of-sample&#8217;&#8217; test of CMIP5 emergent constraints, it does provide us with a new dataset composed of new and/or more advanced models in which to assess their robustness. This presentation will review the proposed emergent constraints on the large-scale atmospheric circulation and assess whether or not they are robust across both the CMIP5 and CMIP6 ensembles. Their potential for constraining regional hydroclimate projections will also be discussed.&#160;

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Variability of large-scale atmospheric circulation indices for the northern hemisphere during the past 100 years

Meteorologische Zeitschrift ◽

10.1127/0941-2948/2009/0389 ◽

2009 ◽

Vol 18 (4) ◽

pp. 379-396 ◽

Cited By ~ 25

Author(s):

Stefan Brönnimann ◽

Alexander Stickler ◽

Thomas Griesser ◽

Andreas M. Fischer ◽

Andrea Grant ◽

...

Keyword(s):

Atmospheric Circulation ◽

Northern Hemisphere ◽

Large Scale ◽

The Past ◽

Atmospheric Circulation Indices ◽

Circulation Indices ◽

Large Scale Atmospheric Circulation

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Precipitation variability in the Meuse basin in relation to atmospheric circulation

Water Science & Technology ◽

10.2166/wst.2005.0096 ◽

2005 ◽

Vol 51 (5) ◽

pp. 5-14 ◽

Cited By ~ 10

Author(s):

M. Tu ◽

P.J.M. de Laat ◽

M.J. Hall ◽

M.J.M. de Wit

Keyword(s):

Statistical Analysis ◽

Atmospheric Circulation ◽

Large Scale ◽

Precipitation Variability ◽

Past Century ◽

The Past ◽

Winter Half ◽

Summer Half ◽

Large Scale Atmospheric Circulation ◽

Precipitation Events

The distribution of precipitation events in the Meuse basin during the past century has been found to reflect the large-scale atmospheric circulation, as characterised by the Grosswetterlagen system. Statistical analysis of the long observation records (1911–2002) for the basin showed that although the annual (November to October) and winter half-year (November to April) frequencies of wet days (≥1 mm/day) were nearly stable, the associated precipitation amounts have significantly increased since 1980. From 1980 onwards, the very wet days (≥10 mm/day) in the winter half-year have become more frequent. No obvious change was identified for the summer half-year (May to October) very wet days. Both the precipitation amounts of wet and very wet days in the winter half-year and the occurrence of associated atmospheric circulation of the types/sub-types west cyclone, southwest cyclone and northwest cyclone showed a significant increase around 1980.

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Projections of northern hemisphere extratropical climate underestimate internal variability and associated uncertainty

Communications Earth & Environment ◽

10.1038/s43247-021-00268-7 ◽

2021 ◽

Vol 2 (1) ◽

Author(s):

Christopher H. O’Reilly ◽

Daniel J. Befort ◽

Antje Weisheimer ◽

Tim Woollings ◽

Andrew Ballinger ◽

...

Keyword(s):

Climate Variability ◽

Atmospheric Circulation ◽

Large Scale ◽

Climate Models ◽

Regional Climate ◽

Coupled Model ◽

Internal Variability ◽

Uncertainty Range ◽

Coupled Climate Models ◽

Large Scale Atmospheric Circulation

AbstractInternal climate variability will play a major role in determining change on regional scales under global warming. In the extratropics, large-scale atmospheric circulation is responsible for much of observed regional climate variability, from seasonal to multidecadal timescales. However, the extratropical circulation variability on multidecadal timescales is systematically weaker in coupled climate models. Here we show that projections of future extratropical climate from coupled model simulations significantly underestimate the projected uncertainty range originating from large-scale atmospheric circulation variability. Using observational datasets and large ensembles of coupled climate models, we produce synthetic ensemble projections constrained to have variability consistent with the large-scale atmospheric circulation in observations. Compared to the raw model projections, the synthetic observationally-constrained projections exhibit an increased uncertainty in projected 21st century temperature and precipitation changes across much of the Northern extratropics. This increased uncertainty is also associated with an increase of the projected occurrence of future extreme seasons.

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