Resolving the Dust Bowl paradox of grassland responses to extreme drought

During the 1930s Dust Bowl drought in the central United States, species with the C3photosynthetic pathway expanded throughout C4-dominated grasslands. This widespread increase in C3grasses during a decade of low rainfall and high temperatures is inconsistent with well-known traits of C3vs. C4pathways. Indeed, water use efficiency is generally lower, and photosynthesis is more sensitive to high temperatures in C3than C4species, consistent with the predominant distribution of C3grasslands in cooler environments and at higher latitudes globally. We experimentally imposed extreme drought for 4 y in mixed C3/C4grasslands in Kansas and Wyoming and, similar to Dust Bowl observations, also documented three- to fivefold increases in C3/C4biomass ratios. To explain these paradoxical responses, we first analyzed long-term climate records to show that under nominal conditions in the central United States, C4grasses dominate where precipitation and air temperature are strongly related (warmest months are wettest months). In contrast, C3grasses flourish where precipitation inputs are less strongly coupled to warm temperatures. We then show that during extreme drought years, precipitation–temperature relationships weaken, and the proportion of precipitation falling during cooler months increases. This shift in precipitation seasonality provides a mechanism for C3grasses to respond positively to multiyear drought, resolving the Dust Bowl paradox. Grasslands are globally important biomes and increasingly vulnerable to direct effects of climate extremes. Our findings highlight how extreme drought can indirectly alter precipitation seasonality and shift ecosystem phenology, affecting function in ways not predictable from key traits of C3and C4species.

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Aeroallergens and Climate Change in Tulsa, Oklahoma: Long-Term Trends in the South Central United States

Frontiers in Allergy ◽

10.3389/falgy.2021.726445 ◽

2021 ◽

Vol 2 ◽

Author(s):

Estelle Levetin

Keyword(s):

Climate Change ◽

United States ◽

Pollen Season ◽

Maximum Temperature ◽

The South ◽

South Central ◽

Pollen Types ◽

Central United States ◽

Total Pollen

Climate change is having a significant effect on many allergenic plants resulting in increased pollen production and shifts in plant phenology. Although these effects have been well-studied in some areas of the world, few studies have focused on long-term changes in allergenic pollen in the South Central United States. This study examined airborne pollen, temperature, and precipitation in Tulsa, Oklahoma over 25 to 34 years. Pollen was monitored with a Hirst-type spore trap on the roof of a building at the University of Tulsa and meteorology data were obtained from the National Weather Service. Changes in total pollen intensity were examined along with detailed analyses of the eight most abundant pollen types in the Tulsa atmosphere. In addition to pollen intensity, changes in pollen season start date, end date, peak date and season duration were also analyzed. Results show a trend to increasing temperatures with a significant increase in annual maximum temperature. There was a non-significant trend toward increasing total pollen and a significant increase in tree pollen over time. Several individual taxa showed significant increases in pollen intensity over the study period including spring Cupressaceae and Quercus pollen, while Ambrosia pollen showed a significant decrease. Data from the current study also indicated that the pollen season started earlier for spring pollinating trees and Poaceae. Significant correlations with preseason temperature may explain the earlier pollen season start dates along with a trend toward increasing March temperatures. More research is needed to understand the global impact of climate change on allergenic species, especially from other regions that have not been studied.

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Understanding recurrent land use processes and long-term transitions in the dynamic south-central United States, c. 1800 to 2006

Land Use Policy ◽

10.1016/j.landusepol.2017.07.061 ◽

2017 ◽

Vol 68 ◽

pp. 345-354 ◽

Cited By ~ 2

Author(s):

Mark A. Drummond ◽

Glenn E. Griffith ◽

Roger F. Auch ◽

Michael P. Stier ◽

Janis L. Taylor ◽

...

Keyword(s):

United States ◽

Land Use ◽

South Central ◽

Central United States

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Probability of compound climate extremes in a changing climate: A copula-based study of hot, dry, and windy events in the central United States

Environmental Research Letters ◽

10.1088/1748-9326/abb1ef ◽

2020 ◽

Vol 15 (10) ◽

pp. 104058 ◽

Cited By ~ 1

Author(s):

Ameneh Tavakol ◽

Vahid Rahmani ◽

John Harrington Jr.

Keyword(s):

United States ◽

Climate Extremes ◽

Changing Climate ◽

Central United States

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A Water Balance–Based, Spatiotemporal Evaluation of Terrestrial Evapotranspiration Products across the Contiguous United States

Journal of Hydrometeorology ◽

10.1175/jhm-d-17-0186.1 ◽

2018 ◽

Vol 19 (5) ◽

pp. 891-905 ◽

Cited By ~ 3

Author(s):

Elizabeth Carter ◽

Christopher Hain ◽

Martha Anderson ◽

Scott Steinschneider

Keyword(s):

United States ◽

Energy Balance ◽

Interannual Variability ◽

Water Budget ◽

Water Budgets ◽

Central United States ◽

Precipitation Estimates ◽

Terrestrial Water ◽

Gauged Basins

Abstract Accurate gridded estimates of evapotranspiration (ET) are essential to the analysis of terrestrial water budgets. In this study, ET estimates from three gridded energy balance–based products (ETEB) with independent model formations and data forcings are evaluated for their ability to capture long-term climatology and interannual variability in ET derived from a terrestrial water budget (ETWB) for 671 gauged basins across the contiguous United States. All three ETEB products have low spatial bias and accurately capture interannual variability of ETWB in the central United States, where ETEB and ancillary estimates of change in total surface water storage (ΔTWS) from the GRACE satellite project appear to close terrestrial water budgets. In humid regions, ETEB products exhibit higher long-term bias, and the covariability of ETEB and ETWB decreases significantly. Several factors related to either failure of ETWB, such as errors in ΔTWS and precipitation, or failure of ETEB, such as treatment of snowfall and horizontal heat advection, explain some of these discrepancies. These results mirror and build on conclusions from other studies: on interannual time scales, ΔTWS and error in precipitation estimates are nonnegligible uncertainties in ET estimates based on a terrestrial water budget, and this confounds their comparison to energy balance ET models. However, there is also evidence that in at least some regions, climate and landscape features may also influence the accuracy and long-term bias of ET estimates from energy balance models, and these potential errors should be considered when using these gridded products in hydrologic applications.

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A New Look at the Variance of Summertime Temperatures over Land

Journal of Climate ◽

10.1175/jcli-d-19-0887.1 ◽

2020 ◽

Vol 33 (13) ◽

pp. 5465-5477 ◽

Cited By ~ 1

Author(s):

Lucas R. Vargas Zeppetello ◽

David S. Battisti ◽

Marcia B. Baker

Keyword(s):

Climate Change ◽

United States ◽

Heat Flux ◽

Surface Temperature ◽

Shortwave Radiation ◽

Climatic Warming ◽

Temperature Variance ◽

Central United States ◽

Very High

AbstractThe increasing frequency of very high summertime temperatures has motivated growing interest in the processes determining the probability distribution of surface temperature over land. Here, we show that on monthly time scales, temperature anomalies can be modeled as linear responses to fluctuations in shortwave radiation and precipitation. Our model contains only three adjustable parameters, and, surprisingly, these can be taken as constant across the globe, notwithstanding large spatial variability in topography, vegetation, and hydrological processes. Using observations of shortwave radiation and precipitation from 2000 to 2017, the model accurately reproduces the observed pattern of temperature variance throughout the Northern Hemisphere midlatitudes. In addition, the variance in latent heat flux estimated by the model agrees well with the few long-term records that are available in the central United States. As an application of the model, we investigate the changes in the variance of monthly averaged surface temperature that might be expected due to anthropogenic climate change. We find that a climatic warming of 4°C causes a 10% increase in temperature variance in parts of North America.

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Influence of eastern Pacific and central Pacific El Niño events on winter climate extremes over the eastern and central United States

International Journal of Climatology ◽

10.1002/joc.4321 ◽

2015 ◽

Vol 35 (15) ◽

pp. 4756-4770 ◽

Cited By ~ 20

Author(s):

Liang Ning ◽

Raymond S. Bradley

Keyword(s):

United States ◽

El Nino ◽

Climate Extremes ◽

Eastern Pacific ◽

Central Pacific ◽

Central Pacific El Niño ◽

Winter Climate ◽

Central United States ◽

El Niño Events ◽

El Nino Events

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The Relationship between Cool and Warm Season Moisture over the Central United States, 1685–2015

Journal of Climate ◽

10.1175/jcli-d-17-0593.1 ◽

2018 ◽

Vol 31 (19) ◽

pp. 7909-7924 ◽

Cited By ~ 3

Author(s):

Max C. A. Torbenson ◽

David W. Stahle

Keyword(s):

United States ◽

Soil Moisture ◽

Tree Ring ◽

Land Surface ◽

Warm Season ◽

Instrumental Record ◽

Moisture Balance ◽

Central United States ◽

The Relationship

Land surface feedbacks impart a significant degree of persistence between cool and warm season moisture availability in the central United States. However, the degree of correlation between these two variables is subject to major changes that appear to occur on decadal to multidecadal time scales, even in the relatively short 115-yr instrumental record. Tree-ring reconstructions have extended the limited observational record of long-term soil moisture levels, but such reconstructions do not resolve the seasonal differences in moisture conditions. We present two separate 331-yr-long seasonal moisture reconstructions for the central United States, based on sensitive subannual and annual tree-ring chronologies that have strong and separate seasonal moisture signals: an estimate of the long-term May soil moisture balance and a second estimate of the short-term June–August atmospheric moisture balance. The predictors used in each seasonal reconstruction are not significantly correlated with the alternate season target. Both reconstructions capture over 70% of the interannual variance in the instrumental data for the calibration period and also share significant decadal and multidecadal variability with the instrumental record in both the calibration and validation periods. The instrumental and reconstructed moisture levels are both positively correlated between spring and summer strongly enough to have potential value in seasonal prediction. However, the relationship between spring and summer moisture exhibits major decadal changes in strength and even sign that appear to be related to large-scale ocean–atmosphere dynamics associated with the Atlantic multidecadal oscillation.

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Influence of the Ocean and Greenhouse Gases on Severe Drought Likelihood in the Central United States in 2012

Journal of Climate ◽

10.1175/jcli-d-16-0294.1 ◽

2017 ◽

Vol 30 (5) ◽

pp. 1789-1806 ◽

Cited By ~ 4

Author(s):

David E. Rupp ◽

Sihan Li ◽

Philip W. Mote ◽

Neil Massey ◽

Sarah N. Sparrow ◽

...

Keyword(s):

United States ◽

Soil Moisture ◽

Greenhouse Gases ◽

Extreme Drought ◽

Exceedance Probability ◽

Soil Moisture Deficit ◽

Anthropogenic Forcing ◽

Moisture Deficit ◽

Central United States ◽

Sst Anomalies

Abstract The impacts of sea surface temperature (SST) anomalies and anthropogenic greenhouse gases on the likelihood of extreme drought occurring in the central United States in the year 2012 were investigated using large-ensemble simulations from a global atmospheric climate model. Two sets of experiments were conducted. In the first, the simulated hydroclimate of 2012 was compared to a baseline period (1986–2014) to investigate the impact of SSTs. In the second, the hydroclimate in a world with 2012-level anthropogenic forcing was compared to five “counterfactual” versions of a 2012 world under preindustrial forcing. SST anomalies in 2012 increased the simulated likelihood of an extreme summer precipitation deficit (e.g., the deficit with a 2% exceedance probability) by a factor of 5. The likelihood of an extreme summer soil moisture deficit increased by a similar amount, due in great part to a large spring soil moisture deficit carrying over into summer. An anthropogenic impact on precipitation was detectable in the simulations, doubling the likelihood of what would have been a rainfall deficit with a 2% exceedance probability under preindustrial-level forcings. Despite this reduction in rainfall, summer soil moisture during extreme drought was essentially unaffected by anthropogenic forcing because of 1) evapotranspiration declining roughly one-to-one with a decrease in precipitation due to severe water supply constraint and despite higher evaporative demand and 2) a decrease in stomatal conductance, and therefore a decrease in potential transpiration, with higher atmospheric CO2 concentrations.

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Flash Drought as Captured by Reanalysis Data: Disentangling the Contributions of Precipitation Deficit and Excess Evapotranspiration

Journal of Hydrometeorology ◽

10.1175/jhm-d-18-0242.1 ◽

2019 ◽

Vol 20 (6) ◽

pp. 1241-1258 ◽

Cited By ~ 8

Author(s):

R. D. Koster ◽

S. D. Schubert ◽

H. Wang ◽

S. P. Mahanama ◽

Anthony M. DeAngelis

Keyword(s):

United States ◽

Soil Moisture ◽

Extreme Precipitation ◽

Land Surface ◽

Heat Waves ◽

Reanalysis Data ◽

Land System ◽

Central United States ◽

Surface Drying

Abstract Flash droughts—uncharacteristically rapid dryings of the land system—are naturally associated with extreme precipitation deficits. Such precipitation deficits, however, do not tell the whole story, for land surface drying can be exacerbated by anomalously high evapotranspiration (ET) rates driven by anomalously high temperatures (e.g., during heat waves), anomalously high incoming radiation (e.g., from reduced cloudiness), and other meteorological anomalies. In this study, the relative contributions of precipitation and ET anomalies to flash drought generation in the Northern Hemisphere are quantified through the analysis of diagnostic fields contained within the MERRA-2 reanalysis product. Unique to the approach is the explicit treatment of soil moisture impacts on ET through relationships diagnosed from the reanalysis data; under this treatment, an ET anomaly that is negative relative to the local long-term climatological mean is still considered positive in terms of its contribution to a flash drought if it is high for the concurrent value of soil moisture. Maps produced in the analysis show the fraction of flash drought production stemming specifically from ET anomalies and illustrate how ET anomalies for some droughts are related to temperature and radiation anomalies. While ET is found to have an important impact on flash drought production in the central United States and in parts of Russia known from past studies to be prone to heat wave–related drought, and while this impact does appear stronger during the onset (first several days) of flash droughts, overall the contribution of ET to these droughts is small relative to the contribution of precipitation deficit.

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