The seasonality of precipitation signals embedded within the North American Drought Atlas

George, Scott St.; Meko, David M.; Cook, Edward R.

doi:10.1177/0959683610365937

Cited by 85 publications

(70 citation statements)

References 41 publications

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“…JJA PDSI reflects hydroclimate conditions for the past 12-18 months because of persistence built into the PDSI calculation, and as a consequence, precipitation biases in both seasons will impact PDSI. Nevertheless, tree ring-reconstructed PDSI has been shown to predominately reflect winter season precipitation variability over the NASW region (St. George et al 2010;Griffin et al 2013), a characteristic that is likely shared by the models. If this is the case, the impact of underestimating summer precipitation on comparisons between model and reconstructed PDSI may be minimal.…”

Section: B Model Biases and Pdsimentioning

confidence: 99%

Are Simulated Megadroughts in the North American Southwest Forced?*

et al. 2014

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Multidecadal drought periods in the North American Southwest (258-42.58N, 1258-1058W), so-called megadroughts, are a prominent feature of the paleoclimate record over the last millennium (LM). Six forced transient simulations of the LM along with corresponding historical and 500-yr preindustrial control runs from phase 5 of the Coupled Model Intercomparison Project (CMIP5) are analyzed to determine if atmosphere-ocean general circulation models (AOGCMs) are able to simulate droughts that are similar in persistence and severity to the megadroughts in the proxy-derived North American Drought Atlas. Megadroughts are found in each of the AOGCM simulations of the LM, although there are intermodel differences in the number, persistence, and severity of these features. Despite these differences, a common feature of the simulated megadroughts is that they are not forced by changes in the exogenous forcing conditions. Furthermore, only the Community Climate System Model (CCSM), version 4, simulation contains megadroughts that are consistently forced by cooler conditions in the tropical Pacific Ocean. These La Niña-like mean states are not accompanied by changes to the interannual variability of the El Niño-Southern Oscillation system and result from internal multidecadal variability of the tropical Pacific mean state, of which the CCSM has the largest magnitude of the analyzed simulations. Critically, the CCSM is also found to have a realistic teleconnection between the tropical Pacific and North America that is stationary on multidecadal time scales. Generally, models with some combination of a realistic and stationary teleconnection and large multidecadal variability in the tropical Pacific are found to have the highest incidence of megadroughts driven by the tropical Pacific boundary conditions.

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Section: B Model Biases and Pdsimentioning

confidence: 99%

Are Simulated Megadroughts in the North American Southwest Forced?*

et al. 2014

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“…Positive values of PDSI indicate wetterthan-normal conditions and negative values indicate drier-than-normal conditions. Because PDSI has a memory time scale of 12-18 months (Guttman 1998;VicenteSerrano et al 2010), values during the summer season will reflect temperature and precipitation anomalies from throughout the year (e.g., St. George et al 2010).…”

Section: A the North American Drought Atlasmentioning

confidence: 99%

Pan-Continental Droughts in North America over the Last Millennium*

et al. 2014

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Regional droughts are common in North America, but pan-continental droughts extending across multiple regions, including the 2012 event, are rare relative to single-region events. Here, the tree-ring-derived North American Drought Atlas is used to investigate drought variability in four regions over the last millennium, focusing on pan-continental droughts. During the Medieval Climate Anomaly (MCA), the central plains (CP), Southwest (SW), and Southeast (SE) regions experienced drier conditions and increased occurrence of droughts and the Northwest (NW) experienced several extended pluvials. Enhanced MCA aridity in the SW and CP manifested as multidecadal megadroughts. Notably, megadroughts in these regions differed in their timing and persistence, suggesting that they represent regional events influenced by local dynamics rather than a unified, continental-scale phenomena. There is no trend in pan-continental drought occurrence, defined as synchronous droughts in three or more regions. SW, CP, and SE (SW1CP1SE) droughts are the most common, occurring in 12% of all years and peaking in prevalence during the twelfth and thirteenth centuries; patterns involving three other regions occur in about 8% of years. Positive values of the Southern Oscillation index (La Niña conditions) are linked to SW, CP, and SE (SW1CP1SE) droughts and SW, CP, and NW (SW1CP1NW) droughts, whereas CP, NW, and SE (CP1NW1SE) droughts are associated with positive values of the Pacific decadal oscillation and Atlantic multidecadal oscillation. While relatively rare, pancontinental droughts are present in the paleo record and are linked to defined modes of climate variability, implying the potential for seasonal predictability. Assuming stable drought teleconnections, these events will remain an important feature of future North American hydroclimate, possibly increasing in their severity in step with other expected hydroclimate responses to increased greenhouse gas forcing. IntroductionDuring the summer of 2012, over half of the continental United States experienced moderate-to-severe drought conditions, with the core of the drought area extending across Mexico and the desert Southwest, the central plains, and the southeastern United States (Fig. 1). At its peak in July, the drought covered 61.8% of the contiguous United States (NCDC 2013a), exceeding the 99th percentile of drought-covered area observed during the full period of observation (from 1895 to the present). Notably, the area of the United States classified by the National Climatic Data Center (NCDC) as ''moderately to extremely dry'' exceeded the July 2012 area in only eight other months during the instrumental record (see http://www1.ncdc.noaa.gov/pub/data/cmb/sotc/drought/ 2012/13/uspctarea-wetdry-mod.txt): April-October 1934 and December 1939, all during the Dust Bowl drought of the 1930s.Drought is a common and recurrent feature of North American climate (e.g., Cook et al. 2007; McCabe et al. 2004;Nigam et al. 2011; Schubert et al. 2004a,b;Seager et al. 2005), but pan-...

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“…The season of climate information recorded by trees varies geographically as well as by species and elevation [e.g., St . George et al ., ]. Many trees strongly reflect cool‐season climate due to factors such as food accumulation in trees over the cool season or influence of climate on cambial activation.…”

Section: Discussionmentioning

confidence: 99%

“…Recent studies [e.g., St . George et al ., ] have raised important concerns about the seasonality recorded in paleoclimate proxies and how this might influence the interpretation of past events. To assess differences among CFR methods with respect to model performance in different seasons, each of the climate variables were averaged over both the cool season (from October to March, hereafter OM) and warm season (from April to September, hereafter AS), thus yielding six distinct data sets (one for each variable‐season pair).…”

Section: Methodsmentioning

confidence: 99%

Performance of climate field reconstruction methods over multiple seasons and climate variables

Dannenberg

Wise

2013

JGR Atmospheres

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[1] Studies of climate variability require long time series of data but are limited by the absence of preindustrial instrumental records. For such studies, proxy-based climate reconstructions, such as those produced from tree-ring widths, provide the opportunity to extend climatic records into preindustrial periods. Climate field reconstruction (CFR) methods are capable of producing spatially-resolved reconstructions of climate fields.We assessed the performance of three commonly used CFR methods (canonical correlation analysis, point-by-point regression, and regularized expectation maximization) over spatially-resolved fields using multiple seasons and climate variables. Warm-and cool-season geopotential height, precipitable water, and surface temperature were tested for each method using tree-ring chronologies. Spatial patterns of reconstructive skill were found to be generally consistent across each of the methods, but the robustness of the validation metrics varied by CFR method, season, and climate variable. The most robust validation metrics were achieved with geopotential height, the October through March temporal composite, and the Regularized Expectation Maximization method. While our study is limited to assessment of skill over multidecadal (rather than multi-centennial) time scales, our findings suggest that the climate variable of interest, seasonality, and spatial domain of the target field should be considered when assessing potential CFR methods for real-world applications.Citation: Dannenberg, M. P., and E. K. Wise (2013), Performance of climate field reconstruction methods over multiple seasons and climate variables, J. Geophys. Res. Atmos., 118,[9595][9596][9597][9598][9599][9600][9601][9602][9603][9604][9605][9606][9607][9608][9609][9610]

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The seasonality of precipitation signals embedded within the North American Drought Atlas

Cited by 85 publications

References 41 publications

Are Simulated Megadroughts in the North American Southwest Forced?*

Are Simulated Megadroughts in the North American Southwest Forced?*

Pan-Continental Droughts in North America over the Last Millennium*

Performance of climate field reconstruction methods over multiple seasons and climate variables

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