Pacific Ocean Forcing and Atmospheric Variability Are the Dominant Causes of Spatially Widespread Droughts in the Contiguous United States

Baek, Seung H.; Smerdon, Jason E.; Seager, Richard; Williams, A. Park; Cook, Benjamin I.

doi:10.1029/2018jd029219

Cited by 12 publications

(19 citation statements)

References 90 publications

(133 reference statements)

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“…This validation of the PHYDA with regard to pan‐CONUS droughts supports prior validation exercises that have found the PHYDA and NADA to have strong grid‐level correlations from 1500 ‐ 2000 CE (Steiger et al, ) and further supports our use of the PHYDA as a new product in the current study. Regarding the ocean forcing of pan‐CONUS droughts, our analysis of the PHYDA corroborates the key model‐based findings in Baek et al () based on the instrumental period, namely, that pan‐CONUS droughts exhibit a robust association with cold Pacific conditions but not with warm Atlantic conditions. Our analyses and those of Baek et al () thus tell a consistent story across multiple centuries about the oceanic causes of pan‐CONUS droughts.…”

Section: Discussionsupporting

confidence: 88%

“…A key caveat of our results is that the PHYDA and the SST-forced models analyzed in Baek et al (2019) are both based on NCAR models, the former employing the NCAR LME (Otto-Bliesner et al, 2016) in the data assimilation process and the latter being direct simulations from the NCAR CAM5. Further studies are therefore necessary to assess whether the results outlined herein and in Baek et al (2019) are robust to model choices. This caveat notwithstanding, a potential point of reconciliation between our results and the canonical understanding of Atlantic influences, may be that the relative influences of the Pacific and Atlantic Oceans on North American hydroclimate vary over interannual and multidecadal timescales.…”

Section: 1029/2019gl082838mentioning

confidence: 99%

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Oceanic Drivers of Widespread Summer Droughts in the United States Over the Common Era

Baek

Steiger

Smerdon

et al. 2019

Geophysical Research Letters

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We examine oceanic drivers of widespread droughts over the contiguous United States (herein pan‐CONUS droughts) during the Common Era in what is one of the first analyses of the new Paleo Hydrodynamics Data Assimilation (PHYDA) product. The canonical understanding of oceanic influences on North American hydroclimate suggests that pan‐CONUS droughts are forced by a contemporaneous cold tropical Pacific Ocean and a warm tropical Atlantic Ocean. We test this hypothesis using the paleoclimate record. Composite analyses find a robust association between pan‐CONUS drought events and cold tropical Pacific conditions, but not with warm Atlantic conditions. Similarly, a self‐organizing map analysis shows that pan‐CONUS drought years are most commonly associated with a global sea surface temperature pattern displaying strong La Niña and cold Atlantic Multidecadal Oscillation (AMO) conditions. Our results confirm previous model‐based findings for the instrumental period and show that cold tropical Pacific Ocean conditions are the principal driver of pan‐CONUS droughts on annual timescales.

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Section: Discussionsupporting

confidence: 88%

Section: 1029/2019gl082838mentioning

confidence: 99%

Oceanic Drivers of Widespread Summer Droughts in the United States Over the Common Era

Baek

Steiger

Smerdon

et al. 2019

Geophysical Research Letters

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“…For the different drought cluster types, we measure the empirical distributions of monthly areas and intensities and their positive monthly rates of change (i.e., increases in area and intensity). Drought onset and development are characterized by growth and intensification, so comparing how these behaviors vary across drought cluster types may provide insights into their underlying mechanisms (Baek et al, 2019;Findell & Delworth, 2010;Giannini et al, 2003;Hoerling & Kumar, 2009;Kam et al, 2013;Schubert et al, 2009Schubert et al, , 2016Sheffield & Wood, 2011;Wood et al, 2015). Conversely, negative changes in area and intensity-which are associated with drought recovery-are likely to be governed by mechanisms that are independent from This frequency F in ocean grid cell i is the ratio between the number of Landfalling drought clusters that started in the grid cell n i,o divided by the number of years in the study, N years .…”

Section: Comparison Of Cluster Dynamics Across Drought Typesmentioning

confidence: 99%

“…Kumar, 2009;Kam et al, 2014;Schubert et al, 2009Schubert et al, , 2016Veldkamp et al, 2015). These teleconnections account for 10-60% of precipitation variability over different regions and seasons (Baek et al, 2019;Schubert et al, 2016), with the remaining variance attributed to internal atmospheric variability (Baek et al, 2019) and land-atmosphere feedbacks (Klingaman et al, 2008;Seneviratne et al, 2010).…”

Section: Introductionmentioning

confidence: 99%

Landfalling Droughts: Global Tracking of Moisture Deficits From the Oceans Onto Land

Herrera-Estrada

Diffenbaugh

2020

Water Resources Research

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Droughts threaten food, energy, and water security, causing death and displacement of millions of people and billions of dollars in damages. However, there are still important gaps in the understanding of drought mechanisms and behaviors, inhibiting the accuracy of early-warning systems designed to protect communities worldwide. We use an object-tracking algorithm to track clusters of precipitation-minus-evaporation moisture deficits across land and ocean areas of the globe from 1981-2018. This analysis reveals a new type of "landfalling drought" that originates over the ocean and "migrates" onto land. We find that 16% of droughts that affected the continents worldwide from 1981-2018 were landfalling droughts. These droughts were significantly larger (220-425%) and more intense (4-30%)-and grew (253-285%) and intensified (9-28%) faster-than droughts that developed solely over the land or ocean. To identify potential underlying mechanisms, we analyze moisture transport associated with landfalling droughts over western North America. We find that landfalling droughts in this region are associated with anomalously anticyclonic atmospheric pressure patterns that reduce moisture fluxes over the Pacific Ocean toward the continent. By advancing understanding of the spatiotemporal evolution of droughts, our findings offer the potential to improve seasonal-scale prediction and long-term projection of global drought risks. Plain Language Summary Droughts can have devastating impacts on a region's domestic water supply, electricity generation, agriculture, and ecosystem health. However, the processes by which droughts arise, develop, and end are not yet fully understood, creating barriers for accurate prediction. In this study, we define droughts as instances when the quantity of precipitation minus evaporation is below normal, allowing us to identify droughts over both the land and ocean. Tracking droughts from where they start to where they end reveals that 16% of droughts that affect continents start over the ocean and travel onto land. We find that these "landfalling droughts" are larger, more intense, and grow faster after making landfall, compared to droughts that start and end completely over land. While the role of sea surface temperatures has been studied in relation to drought development over the continents, fewer studies have analyzed moisture deficits over the oceans. Our results suggest that monitoring and tracking moisture deficits offshore has the potential to yield improvements in drought prediction, warning, and preparation. Recent advances in satellite observations, climate modeling, and computing have improved global drought monitoring and forecasting capabilities (Wood et al., 2015). Much of the predictive capacity arises from the ocean's role in drought development (

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“…During the last decade, considerable progress has been achieved in isolating the mechanisms behind multi-annual droughts in the western USA. Both proxy-based studies (Woodhouse and Overpeck, 1998;McCabe et al, 2004;Routson et al, 2016) and model simulations suggest that oceanic forcing by both the Pacific and to lesser degree the Atlantic acts as a trigger (e.g., Schubert et al, 2004aSchubert et al, , b, 2009Seager, 2007;Cook et al, 2008;Kushnir et al, 2010;Seager et al, 2015;Baek et al, 2019). In particular, a cool Pacific and a warm Atlantic, especially in their tropical regions, are conducive to droughts such as the 1930s Dust Bowl drought, demonstrating a combined impact of both ocean basins (Mc-Cabe et al, 2004;Schubert et al, 2004bSchubert et al, , 2009Feng et al, 2008;Kushnir et al, 2010).…”

Section: Introductionmentioning

confidence: 99%

Two types of North American droughts related to different atmospheric circulation patterns

2019

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Abstract. Proxy-based studies suggest that the southwestern USA is affected by two types of summer drought, often termed Dust Bowl-type droughts and 1950s-type droughts. The spatial drought patterns of the two types are distinct. It has been suggested that they are related to different circulation characteristics, but a lack of observation-based data has precluded further studies. In this paper, we analyze multi-annual summer droughts in North America back to 1600 in tree-ring-based drought reconstructions and in a global, monthly three-dimensional reconstruction of the atmosphere. Using cluster analysis of drought indices, we confirm the two main drought types and find a similar catalog of events as previous studies. These two main types of droughts are then analyzed with respect to 2 m temperatures (T2m), sea-level pressure (SLP), and 500 hPa geopotential height (GPH) in boreal summer. 1950s-type droughts are related to a stronger wave train over the Pacific–North American sector than Dust Bowl-type droughts, whereas the latter show the imprint of a poleward-shifted jet and establishment of a Great Plains ridge. The 500 hPa GPH patterns of the two types differ significantly not only over the contiguous United States and Canada but also over the extratropical North Atlantic and the Pacific. Dust Bowl-type droughts are associated with positive GPH anomalies, while 1950s-type droughts exhibit strong negative GPH anomalies. In comparison with 1950s-type droughts, the Dust Bowl-type droughts are characterized by higher sea-surface temperatures (SSTs) in the northern North Atlantic. Results suggest that atmospheric circulation and SST characteristics not only over the Pacific but also over the extratropical North Atlantic affect the spatial pattern of North American droughts.

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Pacific Ocean Forcing and Atmospheric Variability Are the Dominant Causes of Spatially Widespread Droughts in the Contiguous United States

Cited by 12 publications

References 90 publications

Oceanic Drivers of Widespread Summer Droughts in the United States Over the Common Era

Oceanic Drivers of Widespread Summer Droughts in the United States Over the Common Era

Landfalling Droughts: Global Tracking of Moisture Deficits From the Oceans Onto Land

Two types of North American droughts related to different atmospheric circulation patterns

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