Subregionalization of Low-Frequency Summer Drought Variability in the Southeastern United States

Ortegren, Jason T.; Weatherall, Ashley; Maxwell, Justin T.

doi:10.1080/00330124.2013.787008

Cited by 14 publications

(14 citation statements)

References 21 publications

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“…When spatial contiguity cannot be met, adjustments are required to deal with spatially disjointed units or great care is needed in the interpretation of disjoined ‘regions’. For instance, when PCA was applied to regionalize low‐frequency summer drought variability in the southeastern United States, it initially resulted in two ‘splinter’ climate divisions, which were later subjectively assigned to other divisions to maintain spatial contiguity (Ortegren et al , ).…”

Section: Resultsmentioning

confidence: 99%

Assessment of NARCCAP model in simulating rainfall extremes using a spatially constrained regionalization method

Gao

Carbone

Guo

2015

Intl Journal of Climatology

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Capturing the intensity and return period of extreme rainfall events in the historic record and projecting them into the future are essential to managing, planning, and designing infrastructure. In this study, we assess the performance of the combination of four General Circulation Models (GCMs) and six Regional Climate Models (RCMs) that comprise the North American Regional Climate Change Assessment Program (NARCCAP) and evaluate their performance in simulating rainfall extremes in the continental United States. We adopt a regionalization method to objectively delineate 12 regions in the continental United States with relatively homogenous annual maximum 24‐h rainfall patterns from the North American Regional Reanalysis (NARR) data set. We then compare the Intensity–Duration–Frequency (IDF) curves generated from control simulations of NARCCAP models with those from NARR in each of these regions. We find significant spatial variability of model performance. The models perform reasonably well in many parts of the country, but poorly in the southeastern United States. The GCM providing boundary conditions strongly influences results – output from those RCMs driven by the Community Climate System Model (CCSM) and Canadian Global Climate Model version 3 (CGCM3) matched the NARR data best. Performance of individual RCMs also varied, often in response to nudging, wherein the regional model is constrained by the GCM fields. We also measure changes in bias‐corrected IDF curves generated from NARCCAP projections of the future. In most regions, most models project intensified 24‐h rainfall events in the future (exceptions include some model‐projected decreases in southern California, the extreme north‐central US, Florida, and the Texas Plains). This study provides a valuable means of assessing NARCCAP models' performance in simulating rainfall extremes at the regional scale and understanding how the GCMs, RCMs, and spatial variability affect model performance.

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Section: Resultsmentioning

confidence: 99%

Assessment of NARCCAP model in simulating rainfall extremes using a spatially constrained regionalization method

Gao

Carbone

Guo

2015

Intl Journal of Climatology

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“…During PDO+ periods, an anomalous summer anticyclone (associated with a northwestward extension of the western ridge of the North Atlantic Subtropical Anticyclone [NASH]) centered over the Southeast inhibits convection and is associated with drier summers (Li, L. et al, ). Regardless of the phase of the PDO, AMO+ is significantly linked to warm‐season soil moisture and streamflow deficiencies in the Southeast (Enfield et al, ; McCabe et al, ; Ortegren et al, ; Ortegren et al, ; Sutton and Hodson, ). Examples of anomalous drought frequency and long‐term moisture deficits during AMO+ periods include 1840–1880, mid‐1920s–late 1950s, and early 1990s–early 2010s.…”

Section: Drought Variability In the Southeastern Usamentioning

confidence: 99%

“…The concurrent influences of AMO+, including multidecadal regimes of below‐average summer moisture in the Southeast Atlantic coast region (Enfield et al, ; McCabe and Palecki, ; McCabe et al, ; Ortegren et al, ; Ortegren et al, ) as well as increased total numbers of TCs in the Atlantic Basin, and increased numbers of TC landfalls in the Southeast USA (Gulf and Atlantic; Landsea, ), may appear contradictory. But the increased probability of TC landfall is not enough to completely offset the increased probability of summer moisture deficiency.…”

Section: Atlantic Basin Tropical Cyclone Variabilitymentioning

confidence: 99%

“…The most commonly used index of North Atlantic SST variability is the AMO index, which represents the decadally filtered area-average North Atlantic SST anomaly after linear detrending (Knight et al, 2006). The AMO exhibits low-frequency, roughly cyclical variation on time scales of 50-70 years; (Enfield and Mestas-Nuñez, 1999;Enfield et al, 2001;McCabe and Palecki, 2006;McCabe et al, 2004;Ortegren et al, 2011;Ortegren et al, 2014;Sutton and Hodson, 2005). The AMO variability appears to be driven by the North Atlantic component of the global thermohaline circulation (Dima and Lohmann, 2007).…”

Section: Drought Variability In the Southeastern Usamentioning

confidence: 99%

“…In contrast, many studies have identified a significant AMO-climate signal in a wide range of variables in different regions. For example, the AMO is significantly associated with rainfall and river data in the eastern USA (Enfield et al, 2001;McCabe and Palecki, 2006;McCabe et al, 2004), soil moisture in the Southeast (Ortegren et al, 2011;Ortegren et al, 2014), agricultural productivity in the Southeast (Maxwell et al 2013b), northeast Brazil rainfall, Sahel rainfall, Indian monsoon rainfall (Lu et al, 2006;Zhang and Delworth, 2006), and Atlantic TC variability (Knight et al, 2006;Nogueira et al, 2012;Zhang and Delworth, 2006). Coupled ocean-atmosphere global climate models using historic observed SSTs (without imposing AMO variability in the model) reproduce a realistic, long-lived (millennial) AMO as internal variability (Knight et al, 2006;Zhang and Delworth, 2006).…”

Section: Drought Variability In the Southeastern Usamentioning

confidence: 99%

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Spatiotemporal Patterns of Drought/Tropical Cyclone Co‐occurrence in the Southeastern USA: Linkages to North Atlantic Climate Variability

Ortegren

Maxwell

2014

Geography Compass

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Droughts and landfalling tropical cyclones (TCs; tropical depressions, tropical storms, and hurricanes) are important features of the hydroclimate of the southeastern USA at seasonal, interannual, and interdecadal scales. The societal impacts and climatological aspects of both droughts and Atlantic TCs have been widely addressed in the scientific literature. However, in general, previous research has assessed the two phenomena separately. Recently, the spatiotemporal patterns and hydroclimatic impacts of drought amelioration by landfalling TCs have been analyzed for the southeastern USA, as well as the large‐scale dynamic forcing mechanisms that enhance or suppress drought‐TC co‐occurrence. At multidecadal time scales, both droughts and TCs in this region vary in association with several leading modes of basin‐wide and regional climate variability. These climate modes appear to be coherently linked to a background oceanic–atmospheric pattern that either promotes or suppresses the likelihood of both droughts and TC landfalls. The relative frequency of TC landfalls in drought‐stricken areas, the importance of these events in the regional moisture budget, and the potential for future changes in the large‐scale forcing environment raise fundamental questions about possible changes in the hydroclimate of the southeastern USA, where population growth and rising water demand already place strain on freshwater resources. In this article, we provide a review and synthesis of the recent research on variability in drought, landfalling TCs, the characteristics of the space–time association between these two phenomena in the southeastern USA, and the coherent large‐scale oceanic–atmospheric environment that either promotes or suppresses their co‐occurrence. Further, we review Global Climate Model projections related to these factors, and we identify avenues for future research on this important topic.

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Changes in the Mechanisms Causing Rapid Drought Cessation in the Southeastern United States

Maxwell

Knapp

Ortegren

et al. 2017

Geophysical Research Letters

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The synoptic processes that end droughts are poorly understood, yet have significant climatological implications. Here we examined the spatiotemporal patterns of rapid drought cessation (RDC) in the southeastern United States during the1979-2013 warm season (April-November) for three storm types: Frontal, Tropical, and Air mass. We defined RDC as a 1 month shift in soil moisture sufficient to alleviate an existing drought. We found that 73% of all warm-season droughts were ended by RDC events and the three storm-type groups ended droughts over similar spatial areas. Frontal storms were the most frequent mechanism for RDC events, yet their occurrences significantly decreased and were negatively related to increases in Northern Hemisphere air temperatures. Projected future warming in the Northern Hemisphere suggests a continued decline in the frequency and relative contribution of Frontal storms as RDC events, potentially influencing the timing and spatial scale of drought cessation in the southeastern U.S.

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Subregionalization of Low-Frequency Summer Drought Variability in the Southeastern United States

Cited by 14 publications

References 21 publications

Assessment of NARCCAP model in simulating rainfall extremes using a spatially constrained regionalization method

Assessment of NARCCAP model in simulating rainfall extremes using a spatially constrained regionalization method

Spatiotemporal Patterns of Drought/Tropical Cyclone Co‐occurrence in the Southeastern USA: Linkages to North Atlantic Climate Variability

Changes in the Mechanisms Causing Rapid Drought Cessation in the Southeastern United States

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