scholarly journals Climate Change Amplification of Natural Drought Variability: The Historic Mid-Twentieth-Century North American Drought in a Warmer World

2019 ◽  
Vol 32 (17) ◽  
pp. 5417-5436 ◽  
Author(s):  
Benjamin I. Cook ◽  
Richard Seager ◽  
A. Park Williams ◽  
Michael J. Puma ◽  
Sonali McDermid ◽  
...  
Keyword(s):  
Twentieth Century ◽  
North America ◽  
Greenhouse Gas ◽  
Climate Model ◽  
Warm Season ◽  
Internal Variability ◽  
Cold Season ◽  
Severe Drought ◽  
Evaporative Demand ◽  
Southern Plains

AbstractIn the mid-twentieth century (1948–57), North America experienced a severe drought forced by cold tropical Pacific sea surface temperatures (SSTs). If these SSTs recurred, it would likely cause another drought, but in a world substantially warmer than the one in which the original event took place. We use a 20-member ensemble of the GISS climate model to investigate the drought impacts of a repetition of the mid-twentieth-century SST anomalies in a significantly warmer world. Using observed SSTs and mid-twentieth-century forcings (Hist-DRGHT), the ensemble reproduces the observed precipitation deficits during the cold season (October–March) across the Southwest, southern plains, and Mexico and during the warm season (April–September) in the southern plains and the Southeast. Under analogous SST forcing and enhanced warming (Fut-DRGHT, ≈3 K above preindustrial), cold season precipitation deficits are ameliorated in the Southwest and southern plains and intensified in the Southeast, whereas during the warm season precipitation deficits are enhanced across North America. This occurs primarily from greenhouse gas–forced trends in mean precipitation, rather than changes in SST teleconnections. Cold season runoff deficits in Fut-DRGHT are significantly amplified over the Southeast, but otherwise similar to Hist-DRGHT over the Southwest and southern plains. In the warm season, however, runoff and soil moisture deficits during Fut-DRGHT are significantly amplified across the southern United States, a consequence of enhanced precipitation deficits and increased evaporative losses due to warming. Our study highlights how internal variability and greenhouse gas–forced trends in hydroclimate are likely to interact over North America, including how changes in both precipitation and evaporative demand will affect future drought.

scholarly journals An anomalous atmospheric river linked to the late June 2021 western North America heatwave

2022 ◽  
Author(s):  
Ruping Mo ◽  
Hai Lin ◽  
Frédéric Vitart
Keyword(s):  
North America ◽  
Water Vapour ◽  
Warm Season ◽  
Lower Troposphere ◽  
Heavy Precipitation ◽  
Cold Season ◽  
Feedback Mechanism ◽  
Western North America ◽  
Water Vapour Flux ◽  
The North

Abstract Atmospheric rivers (ARs) are long and narrow bands of enhanced water vapour flux concentrated in the lower troposphere. Many studies have documented the important role of cold-season ARs in producing heavy precipitation and triggering extreme flooding in many parts of the world. However, relatively little research has been conducted on the warm-season ARs and their impacts on extreme heatwave development. Here we show an anomalous warm-season AR moving across the North Pacific and its interaction with the western North American heatwave in late June 2021. We call it an “oriental express’’ to highlight its capability to transport tropical moisture to the west coast of North America from sources in Southeast Asia. Its landfall over the Alaska Panhandle lasted for more than two days and resulted in significant spillover of moisture into western Canada. We provide evidence that the injected water vapour was trapped under the heat dome and may have formed a positive feedback mechanism to regulate the heatwave development in western North America.

scholarly journals Effects of Climate Change on Wind-Driven Heavy-Snowfall Events over Eastern North America

2018 ◽  
Vol 31 (22) ◽  
pp. 9037-9054 ◽  
Author(s):  
Tyler P. Janoski ◽  
Anthony J. Broccoli ◽  
Sarah B. Kapnick ◽  
Nathaniel C. Johnson
Keyword(s):  
North America ◽  
Greenhouse Gas ◽  
Climate Model ◽  
Extreme Values ◽  
Global Climate Model ◽  
High Elevation ◽  
Eastern North America ◽  
Winter Storms ◽  
Extreme Wind ◽  
Wind Events

Eastern North America contains densely populated, highly developed areas, making winter storms with strong winds and high snowfall among the costliest storm types. For this reason, it is important to determine how the frequency of high-impact winter storms, specifically, those combining significant snowfall and winds, will change in this region under increasing greenhouse gas concentrations. This study uses a high-resolution coupled global climate model to simulate the changes in extreme winter conditions from the present climate to a future scenario with doubled CO2 concentrations (2XC). In particular, this study focuses on changes in high-snowfall, extreme-wind (HSEW) events, which are defined as the occurrence of 2-day snowfall and high winds exceeding thresholds based on extreme values from the control simulation, where greenhouse gas concentrations remain fixed. Mean snowfall consistently decreases across the entire region, but extreme snowfall shows a more inconsistent pattern, with some areas experiencing increases in the frequency of extreme-snowfall events. Extreme-wind events show relatively small changes in frequency with 2XC, with the exception of high-elevation areas where there are large decreases in frequency. As a result of combined changes in wind and snowfall, HSEW events decrease in frequency in the 2XC simulation for much of eastern North America. Changes in the number of HSEW events in the 2XC environment are driven mainly by changes in the frequency of extreme-snowfall events, with most of the region experiencing decreases in event frequency, except for certain inland areas at higher latitudes.

The Atmospheric Response to Projected Terrestrial Snow Changes in the Late Twenty-First Century

2010 ◽  
Vol 23 (23) ◽  
pp. 6430-6437 ◽  
Author(s):  
Michael A. Alexander ◽  
Robert Tomas ◽  
Clara Deser ◽  
David M. Lawrence
Keyword(s):  
Twentieth Century ◽  
Sea Ice ◽  
Greenhouse Gas ◽  
General Circulation ◽  
Climate Model ◽  
Circulation Model ◽  
Arctic Sea Ice ◽  
First Century ◽  
Model Experiments ◽  
Twenty First Century

Abstract Two atmospheric general circulation model experiments are conducted with specified terrestrial snow conditions representative of 1980–99 and 2080–99. The snow states are obtained from twentieth-century and twenty-first-century coupled climate model integrations under increasing greenhouse gas concentrations. Sea surface temperatures, sea ice, and greenhouse gas concentrations are set to 1980–99 values in both atmospheric model experiments to isolate the effect of the snow changes. The reduction in snow cover in the twenty-first century relative to the twentieth century increases the solar radiation absorbed by the surface, and it enhances the upward longwave radiation and latent and sensible fluxes that warm the overlying atmosphere. The maximum twenty-first-century minus twentieth-century surface air temperature (SAT) differences are relatively small (<3°C) compared with those due to Arctic sea ice changes (∼10°C). However, they are continental in scale and are largest in fall and spring, when they make a significant contribution to the overall warming over Eurasia and North America in the twenty-first century. The circulation response to the snow changes, while of modest amplitude, involves multiple components, including a local low-level trough, remote Rossby wave trains, an annular pattern that is strongest in the stratosphere, and a hemispheric increase in geopotential height.

scholarly journals Summer Climate Change in the Midwest and Great Plains due to Agricultural Development during the Twentieth Century

2019 ◽  
Vol 32 (17) ◽  
pp. 5583-5599 ◽  
Author(s):  
Catherine A. Nikiel ◽  
Elfatih A. B. Eltahir
Keyword(s):  
Twentieth Century ◽  
North America ◽  
Great Plains ◽  
Agricultural Development ◽  
Climate Model ◽  
Decadal Variability ◽  
Ghg Emissions ◽  
The United States ◽  
Summer Temperature ◽  
Reanalysis Dataset

AbstractAgricultural development is among the most significant forms of land-use change globally. In central North America it has consisted of cropland expansion in the early 1900s, yield intensification starting in the 1930s, and the development of large irrigated areas beginning in the 1950s. The area of this study encompasses the Midwest and Great Plains of the United States not only because significant agricultural change has occurred here but also because of the significant cooling (warming hole) there in the midcentury. This study investigates the relative contribution of agricultural development and greenhouse gas (GHG) emissions on the observed patterns of regional changes in summer temperature, precipitation, and evapotranspiration using a long-term twentieth-century reanalysis dataset (CERA-20C) as boundary conditions for simulations with the MIT Regional Climate Model (MRCM). Temperatures in the Great Plains (33°–43°N, 95°–109°W) and the Midwest (38°–48°N, 82°–109°W) would have been significantly higher in the second half of the twentieth century without the influence of agricultural development, largely due to an increase in evaporative cooling. The simulations of precipitation changes reflect a significant influence of global SST teleconnections at decadal time scales. Numerical simulations also demonstrate the competing effects of cropland expansion and yield intensification on shaping the observed pattern of increases in precipitation. Ultimately, a combination of agricultural development and decadal variability of global sea surface temperatures (SST) explains most of the observed variability of summer temperature and precipitation during the twentieth century over central North America.

scholarly journals Australasian Temperature Reconstructions Spanning the Last Millennium

2016 ◽  
Vol 29 (15) ◽  
pp. 5365-5392 ◽  
Author(s):  
Joëlle Gergis ◽  
Raphael Neukom ◽  
Ailie J. E. Gallant ◽  
David J. Karoly
Keyword(s):  
Twentieth Century ◽  
Statistical Methods ◽  
Climate Model ◽  
Warm Season ◽  
Principal Component Regression ◽  
Pairwise Comparison ◽  
Principal Component ◽  
Reconstruction Methods ◽  
Temperature Reconstructions ◽  
Paleoclimate Records

Abstract Multiproxy warm season (September–February) temperature reconstructions are presented for the combined land–ocean region of Australasia (0°–50°S, 110°E–180°) covering 1000–2001. Using between 2 (R2) and 28 (R28) paleoclimate records, four 1000-member ensemble reconstructions of regional temperature are developed using four statistical methods: principal component regression (PCR), composite plus scale (CPS), Bayesian hierarchical models (LNA), and pairwise comparison (PaiCo). The reconstructions are then compared with a three-member ensemble of GISS-E2-R climate model simulations and independent paleoclimate records. Decadal fluctuations in Australasian temperatures are remarkably similar between the four reconstruction methods. There are, however, differences in the amplitude of temperature variations between the different statistical methods and proxy networks. When the R28 network is used, the warmest 30-yr periods occur after 1950 in 77% of ensemble members over all methods. However, reconstructions based on only the longest records (R2 and R3 networks) indicate that single 30- and 10-yr periods of similar or slightly higher temperatures than in the late twentieth century may have occurred during the first half of the millennium. Regardless, the most recent instrumental temperatures (1985–2014) are above the 90th percentile of all 12 reconstruction ensembles (four reconstruction methods based on three proxy networks—R28, R3, and R2). The reconstructed twentieth-century warming cannot be explained by natural variability alone using GISS-E2-R. In this climate model, anthropogenic forcing is required to produce the rate and magnitude of post-1950 warming observed in the Australasian region. These paleoclimate results are consistent with other studies that attribute the post-1950 warming in Australian temperature records to increases in atmospheric greenhouse gas concentrations.

scholarly journals Sensitivity of Twentieth-Century Sahel Rainfall to Sulfate Aerosol and CO2 Forcing

2011 ◽  
Vol 24 (19) ◽  
pp. 4999-5014 ◽  
Author(s):  
Duncan Ackerley ◽  
Ben B. B. Booth ◽  
Sylvia H. E. Knight ◽  
Eleanor J. Highwood ◽  
David J. Frame ◽  
...  
Keyword(s):  
Twentieth Century ◽  
Climate Models ◽  
Internal Variability ◽  
Natural Variability ◽  
Severe Drought ◽  
Relative Role ◽  
Coupled Climate Models ◽  
Large Ensembles ◽  
Drying Trend ◽  
Sahel Rainfall

A full understanding of the causes of the severe drought seen in the Sahel in the latter part of the twentieth-century remains elusive some 25 yr after the height of the event. Previous studies have suggested that this drying trend may be explained by either decadal modes of natural variability or by human-driven emissions (primarily aerosols), but these studies lacked a sufficiently large number of models to attribute one cause over the other. In this paper, signatures of both aerosol and greenhouse gas changes on Sahel rainfall are illustrated. These idealized responses are used to interpret the results of historical Sahel rainfall changes from two very large ensembles of fully coupled climate models, which both sample uncertainties arising from internal variability and model formulation. The sizes of these ensembles enable the relative role of human-driven changes and natural variability on historic Sahel rainfall to be assessed. The paper demonstrates that historic aerosol changes are likely to explain most of the underlying 1940–80 drying signal and a notable proportion of the more pronounced 1950–80 drying.

scholarly journals Spatial and Seasonal Variations in Aridification across Southwest North America

2016 ◽  
Vol 29 (12) ◽  
pp. 4637-4649 ◽  
Author(s):  
Shannon M. Jones ◽  
David S. Gutzler
Keyword(s):  
United States ◽  
North America ◽  
Warm Season ◽  
Cold Season ◽  
Base Flow ◽  
First Century ◽  
Strongly Correlated ◽  
Southwest United States ◽  
The North ◽  
Twenty First Century

Abstract Southwestern North America (SWNA) is projected to become drier in the twenty-first century as both precipitation (P) and evaporation (E) rates change with increasing greenhouse gas concentration. The authors diagnose the relative contributions of changes in P and E to the local surface moisture balance (P − E) in cold and warm halves of the year across SWNA. Trends in P − E vary spatially between the arid southern subregion (mostly northern Mexico) and the more temperate northern subregion (southwest United States), although both subregions exhibit a negative trend in P − E (trending toward more arid conditions) in CMIP5 projections for the twenty-first century. The P − E trend is biggest in the cold season, when much of the base flow to rivers in the southwest United States is generated. The downward trend in cold season P − E across SWNA is caused primarily by increasing E in the north and decreasing P in the south. Decreasing P is the primary contributor to modest warm season drying trends in both northern and southern subregions. Also, P accounts for most of the interannual variability in SWNA P − E and is strongly correlated with modes of oceanic natural variability during the cold season. SWNA aridification is therefore most readily distinguished from the region’s large natural climate variability in the cold season in the northern subregion, where the projected temperature-driven increase in E is greater than the projected decrease in P.

scholarly journals Global precipitation response to changing forcings since 1870

2011 ◽  
Vol 11 (18) ◽  
pp. 9961-9970 ◽  
Author(s):  
A. Bichet ◽  
M. Wild ◽  
D. Folini ◽  
C. Schär
Keyword(s):  
Greenhouse Gas ◽  
Climate Model ◽  
Hydrological Cycle ◽  
Global Climate ◽  
Global Climate Model ◽  
Internal Variability ◽  
Temperature And Precipitation ◽  
Global Land ◽  
Climate Forcings ◽  
Aerosol Emissions

Abstract. Predicting and adapting to changes in the hydrological cycle is one of the major challenges for the 21st century. To better estimate how it will respond to future changes in climate forcings, it is crucial to understand how the hydrological cycle has evolved in the past and why. In our study, we use an atmospheric global climate model with prescribed sea surface temperatures (SSTs) to investigate how, in the period 1870–2005, changing climate forcings have affected the global land temperature and precipitation. We show that between 1870 and 2005, prescribed SSTs (encapsulating other forcings and internal variability) determine the decadal and interannual variabilities of the global land temperature and precipitation, mostly via their influence in the tropics (25° S–25° N). In addition, using simulations with prescribed SSTs and considering the atmospheric response alone, we find that between 1930 and 2005 increasing aerosol emissions have reduced the global land temperature and precipitation by up to 0.4 °C and 30 mm yr−1, respectively, and that between about 1950 and 2005 increasing greenhouse gas concentrations have increased them by up to 0.25 °C and 10 mm yr−1, respectively. Finally, we suggest that between about 1950 and 1970, increasing aerosol emissions had a larger impact on the hydrological cycle than increasing greenhouse gas concentrations.

scholarly journals Changes in Surface Wind Speed over North America from CMIP5 Model Projections and Implications for Wind Energy

2014 ◽  
Vol 2014 ◽  
pp. 1-10 ◽  
Author(s):  
Sujay Kulkarni ◽  
Huei-Ping Huang
Keyword(s):  
Wind Speed ◽  
North America ◽  
Greenhouse Gas ◽  
Climate Models ◽  
Climate Model ◽  
Global Climate ◽  
Global Climate Model ◽  
Surface Wind ◽  
Surface Wind Speed ◽  
Current Estimate

The centennial trends in the surface wind speed over North America are deduced from global climate model simulations in the Climate Model Intercomparison Project—Phase 5 (CMIP5) archive. Using the 21st century simulations under the RCP 8.5 scenario of greenhouse gas emissions, 5–10 percent increases per century in the 10 m wind speed are found over Central and East-Central United States, the Californian Coast, and the South and East Coasts of the USA in winter. In summer, climate models projected decreases in the wind speed ranging from 5 to 10 percent per century over the same coastal regions. These projected changes in the surface wind speed are moderate and imply that the current estimate of wind power potential for North America based on present-day climatology will not be significantly changed by the greenhouse gas forcing in the coming decades.

scholarly journals Old World megadroughts and pluvials during the Common Era

2015 ◽  
Vol 1 (10) ◽  
pp. e1500561 ◽  
Author(s):  
Edward R. Cook ◽  
Richard Seager ◽  
Yochanan Kushnir ◽  
Keith R. Briffa ◽  
Ulf Büntgen ◽  
...  
Keyword(s):  
Mediterranean Basin ◽  
Climate Model ◽  
Internal Variability ◽  
Climate Projections ◽  
Severe Drought ◽  
Old World ◽  
The Common ◽  
The Mediterranean ◽  
Common Era ◽  
The Mediterranean Basin

Climate model projections suggest widespread drying in the Mediterranean Basin and wetting in Fennoscandia in the coming decades largely as a consequence of greenhouse gas forcing of climate. To place these and other “Old World” climate projections into historical perspective based on more complete estimates of natural hydroclimatic variability, we have developed the “Old World Drought Atlas” (OWDA), a set of year-to-year maps of tree-ring reconstructed summer wetness and dryness over Europe and the Mediterranean Basin during the Common Era. The OWDA matches historical accounts of severe drought and wetness with a spatial completeness not previously available. In addition, megadroughts reconstructed over north-central Europe in the 11th and mid-15th centuries reinforce other evidence from North America and Asia that droughts were more severe, extensive, and prolonged over Northern Hemisphere land areas before the 20th century, with an inadequate understanding of their causes. The OWDA provides new data to determine the causes of Old World drought and wetness and attribute past climate variability to forced and/or internal variability.

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