Southern Great Plains Research Articles

Quantifying the contribution of atmospheric circulation to precipitation variability and changes in the US Great Plains and southwest using self-organizing map–analogue

Abstract. The Great Plains and southwest regions of the US are highly vulnerable to precipitation-related climate disasters such as droughts and floods. In this study, we propose a self-organizing map–analogue (SOMA) approach to empirically quantify the contribution of atmospheric moist circulation (mid-tropospheric geopotential and column moisture transport) to the regional precipitation anomalies, variability, and multi-decadal changes. Our results indicate that moist circulation contributes significantly to short-term precipitation variability, accounting for 54 %–61 % of the total variance in these regions, though these contributions vary significantly across seasons. As indicated in previous research, Pacific Decadal Oscillation (PDO) is one of the major climate modes influencing the long-term multi-decadal variation in precipitation. By contrasting three multi-decadal periods (1950–1976, 1977–1998, 1999–2021) with shifting PDO phases and linking the phase shift to self-organizing map (SOM) nodes, we found that circulation changes contribute considerably to the multi-decadal changes in precipitation anomaly in terms of the mean and days of dry and wet extremes, especially for the southern Great Plains (GP) and southwest. However, these circulation-induced changes are not totally related to the PDO phase shift (mostly less than half) since internal variability or anthropogenically induced changes in circulation can also be potential contributors. Our approach improves upon flow analogue and SOM-based methods and provides insights into the contribution of atmospheric circulation to regional precipitation anomalies and variability.

Consumer willingness-to-pay for a resilient electrical grid

The research objective is to estimate consumer willingness to pay (WTP) for electricity grid fortification. Data are from a representative survey of Oklahoma citizens. Extreme weather events, aging utility infrastructure, increased demand for affordable energy, and terrorism threaten the safety and security of the way most citizens access electricity. This study is a first look at public willingness to support energy grid security measures in the United States Southern Great Plains. Findings suggest that consumers would pay an additional $14.69 in monthly utility bills for a fortified grid. This WTP estimate is close to a recent energy bill hike of $14 initiated by local electricity providers. The findings provide policymakers and energy providers with information on consumer willingness to support efforts to modernize the current grid.

Economic Performance of Rainfed Wheat-Double Crop Systems under Weed Competition

AbstractThis study examines the economic performance of rainfed cropping systems endemic to the Southern Great Plains under weed competition. Cropping systems include tilled and no-till wheat-fallow, wheat-soybean, and wheat-sorghum rotations. Net returns from systems are compared under different levels of weed pressure. Producers operating over longer planning horizons would choose to double-crop regardless of the tillage method used and weed pressure level. Producers operating under shorter planning horizons would implement wheat-fallow systems when weed pressure is high and double crop when weed pressure is low.

Trade-off of ecosystem productivity and water use related to afforestation in southcentral USA under climate change

The increase of tree canopy cover due to woody plant encroachment and tree plantations modifies both carbon and water dynamics. The tradeoffs between ecosystem net primary productivity (NPP) and water use with increasing tree cover in different climate conditions, particularly under future climate scenarios, are not well understood. Within the climate transition zone of the southern Great Plains, USA, we used the Soil and Water Assessment Tool+ (SWAT+) to investigate the combined impacts of increasing tree cover and climate change on carbon and water dynamics in three watersheds representing semiarid, subhumid, and humid climates. Model simulations incorporated two land use modifications (Baseline: existing tree cover; Forest +: increasing evergreen tree cover), in conjunction with two climate change projections (the RCP45 and the RCP85), spanning two time periods (historic: 1991–2020; future: 2070–2099). With climate change, the subhumid and humid watersheds exhibited a greater increase in evapotranspiration (ET) and a corresponding reduction in runoff compared to the semi-arid watershed, while the semi-arid and subhumid watersheds encountered pronounced losses in water availability for streams (>200 mm/year) due to increasing tree cover and climate change. With every 1 % increase in tree cover, both NPP and water use efficiency were projected to increase in all three watersheds under both climate change scenarios, with the subhumid watershed demonstrating the largest increases (>0.16 Mg/ha/year and 170 %, respectively). Increasing tree cover within grasslands, either through woody plant expansion or afforestation, boosts ecosystem NPP, particularly in subhumid regions. Nevertheless, this comes with a notable decrease in water resources, a concern made worse by future climate change. While afforestation offers the potential for greater NPP, it also brings heightened water scarcity concerns, highlighting the importance of tailoring carbon sequestration strategies within specific regions to mitigate unintended repercussions on water availability.

Wildfire across agricultural landscapes: farmer and rancher experiences and perceptions in the southern great plains

ABSTRACT Wildfire frequency and intensity has increased across the Southern Great Plains of the United States and other similar landscapes worldwide in part due to climate change. It is important that policymakers, practitioners, and the agricultural community better understand the impact from increased wildfire incidence and severity across different agricultural landscapes. The purpose of this study is to examine the impact of wildfires across an agricultural landscape of the Southern Great Plains. Using primary data collected from semi-structured interviews of farmers and ranchers in the study region, we quantitatively explore farmers’ and ranchers’ perceptions and experiences about wildfires in the Southern Great Plains of the U.S. About 80% of the producers interviewed had directly experienced wildfire on their property, including significant losses to farmer livelihoods, food stocks (crops and livestock), forages, native grasslands, and structures (building and fencing). Many producers perceived wildfire frequency had increased and another megafire event was very likely. To help reduce wildfire risk for producers in the Southern Great Plains more timely education and outreach efforts about wildfire mitigation, organisation of local fire associations, more timely disaster assistance, and innovative insurance solutions would be useful. Key policy highlights Farmers and ranchers face significant wildfire risk in the Southern Great Plains, a grassland dominated landscape, where public and pooled resources for wildfire mitigation and suppression are scarcer. Policymakers and emergency planners need to be aware of the impacts from wildfires on grassland dominated agricultural landscapes, including losses to farmer livelihoods, food stocks (crops and livestock), forages, native grasslands, structures (building and fencing), amongst others that may occur. More research and education concerning wildfire impacts and mitigation on agricultural landscapes needs to be conducted, such as organising local fire associations, more effectively pooling local resources, and innovative insurance solutions.

Case study of a bore wind-ramp event from lidar measurements and HRRR simulations over ARM Southern Great Plains

The rapid change of wind speed and direction on 21 August 2017 is studied using Doppler lidar measurements at five sites of the Atmospheric Radiation Measurement (ARM) Southern Great Plains (SGP) facility in north-central Oklahoma. The Doppler lidar data were investigated along with meteorological variables such as temperature, humidity, and turbulence available from the large suite of instrumentation deployed at the SGP Central Facility (C1) during the Land-Atmosphere Feedback Experiment in August 2017. Lidar measurements at five sites, separated by 55–70 km, allowed us to document the development and evolution of the wind flow over the SGP area, examine synoptic conditions to understand the mechanism that leads to the ramp event, and estimate the ability of the High-Resolution Rapid Refresh model to reproduce this event. The flow feature in question is an atmospheric bore, a small-scale phenomenon that is challenging to represent in models, that was generated by a thunderstorm outflow northwest of the ARM SGP area. The small-scale nature of bores, its impact on power generation, and the modeling challenges associated with representing bores are discussed in this paper. The results also provide information about model errors between sites of different surface and vegetation types.

Precipitation and Temperature Maxima: A Study across the Southern Great Plains Winter Wheat Region

Abstract With the importance of agriculture to the southern Great Plains (SGPs), accurate knowledge of growing season (GS) temperatures and precipitation is critical. Previous research into GS precipitation and temperature maxima leads to the development of the asynchronous difference index (ADI) which identified positive and negative ADI GSs (March–September). The goal of this research is to further investigate the ADI within a specific agricultural region of the SGP, the winter wheat region, and to quantify the temporal evolution of temperature and precipitation during positive and negative ADI GSs. For this, Global Historical Climatology Network (GHCN) daily station data were analyzed across the GS (March–September) from 1900 to 2020. Results show that differences appear in the temperature and precipitation fields when comparing positive and negative GSs. Namely, positive (negative) ADI GSs show positive (negative) precipitation and negative (positive) temperature anomalies early in the GS, with these anomalies flipping in the later portion of the GS. Further, the results of this work show that the depicted changes in temperature and precipitation during positive and negative ADI GSs impact winter wheat yields. Overall, these results analyze the implications of positive and negative ADI GSs on the SGP climate, namely, the impact of the seasonal variability of daily maximum temperature and precipitation on agriculture.

Mechanisms of Low-Level Jet Formation in the U.S. Mid-Atlantic Offshore

Abstract Low-level jets (LLJs), in which the wind speed attains a local maximum at low altitudes, have been found to occur in the U.S. mid-Atlantic offshore, a region of active wind energy deployment as of 2023. In contrast to widely studied regions such as the U.S. southern Great Plains and the California coastline, the mechanisms that underlie LLJs in the U.S. mid-Atlantic are poorly understood. This work analyzes floating lidar data from buoys deployed in the New York Bight to understand the characteristics and causes of coastal LLJs in the region. Application of the Hilbert–Huang transform, a frequency analysis technique, to LLJ case studies reveals that mid-Atlantic jets frequently occur during times of adjustment in synoptic-scale motions, such as large-scale temperature and pressure gradients or frontal passages, and that they do not coincide with motions at the native inertial oscillation frequency. Subsequent analysis with theoretical models of inertial oscillation and thermal winds further reveals that these jets can form in the stationary geostrophic wind profile from horizontal temperature gradients alone—in contrast to canonical LLJs, which arise from low-level inertial motions. Here, inertial oscillation can further modulate the intensity and altitude of the wind speed maximum. Statistical evidence indicates that these oscillations arise from stable stratification and the associated frictional decoupling due to warmer air flowing over a cold sea surface during the springtime land–sea breeze. These results improve our conceptual understanding of mid-Atlantic jets and may be used to better predict low-level wind speed maxima. Significance Statement The purpose of this work is to identify and characterize the atmospheric mechanisms that result in an occasional low-level maximum in the wind speed off the U.S. mid-Atlantic coastline. Our findings show that these low-level jets form due to horizontal temperature gradients arising from fronts and synoptic systems, as well as from the land–sea breeze that forces warmer air over the cold ocean surface. This work aids predictability of such jets, improves our understanding of this coastal environment, and has implications for future deployment of offshore wind energy in this region.

Associations between dust exposure and hospitalizations in a dust-prone city, Lubbock, TX, USA

AbstractAlthough it is a growing area of investigation in the Global Dust Belt, only a few population-level studies have evaluated the human health associations of windblown dust in North America. We investigated whether acute, short-term dust exposures (DE), in Lubbock, Texas (a medium-sized, dust-prone city in the southern Great Plains, USA) were associated with significant increases in hospitalizations on the day of the exposure and up to 7 days afterward. We used the distributed lag non-linear models in time series analysis to describe non-linear relationship between response outcomes and the delayed effects of exposure over time. We found that increased relative risks of hospitalizations for multiple conditions were associated with the two DE approaches that occurred between 2010 and 2014. Consistent with prior studies of dust health effects in other cities in North America, we identified increased hospitalization risks in Lubbock due to neurodegenerative, atherosclerosis, renal, respiratory, asthma, mental, stroke, neoplasms, ischemia, hematologic, musculoskeletal, and associated diseases (aggregation of all causes each associated with at least 5% of hospitalizations) at various dust exposure days. Associations were modified by age, gender, day of the week, and holiday effects. As climate change increases water stresses on dryland agriculture and long periods of drought, dust exposures are likely to increase for residents of dryland cities and with it the likelihood of adverse health effects on people with preexisting conditions. Additional investigations are needed for other dust-prone population centers worldwide to document the health effects of dust exposures and investigate their causes.

Influences of Cloud Microphysics on the Components of Solar Irradiance in the WRF-Solar Model

An accurate forecast of Global Horizontal solar Irradiance (GHI) and Direct Normal Irradiance (DNI) in cloudy conditions remains a major challenge in the solar energy industry. This study focuses on the impact of cloud microphysics on GHI and its partition into DNI and Diffuse Horizontal Irradiance (DHI) using the Weather Research and Forecasting model specifically designed for solar radiation applications (WRF-Solar) and seven microphysical schemes. Three stratocumulus (Sc) and five shallow cumulus (Cu) cases are simulated and evaluated against measurements at the US Department of Energy’s Atmospheric Radiation Measurement (ARM) user facility, Southern Great Plains (SGP) site. Results show that different microphysical schemes lead to spreads in simulated solar irradiance components up to 75% and 350% from their ensemble means in the Cu and Sc cases, respectively. The Cu cases have smaller microphysical sensitivity due to a limited cloud fraction and smaller domain-averaged cloud water mixing ratio compared to Sc cases. Cloud properties also influence the partition of GHI into DNI and DHI, and the model simulates better GHI than DNI and DHI due to a non-physical error compensation between DNI and DHI. The microphysical schemes that produce more accurate liquid water paths and effective radii of cloud droplets have a better overall performance.

Ectoparasitism and Energy Infrastructure Limit Survival of Preadult Golden Eagles in the Southern Great Plains

Ectoparasitism and Energy Infrastructure Limit Survival of Preadult Golden Eagles in the Southern Great Plains

Refractivity Observations from Radar Phase Measurements: The 22 May 2002 Dryline Case during IHOP Project

The dryline, often associated with the development of severe storms in the Southern Great Plains of the United States of America, is a boundary layer phenomenon that occurs when a warm and moist air mass from the Gulf of Mexico meets a hot and dry air mass from the southwest desert area. An accurate knowledge of the water vapor spatio-temporal variability in the lower part of the atmosphere is crucial for a better understanding of the evolution of the dryline. The tropospheric refractivity, directly related to water vapor content, is a proxy for the water vapor content of the troposphere. It has already been demonstrated that the refractivity and the refractivity vertical gradient can be jointly estimated from radar phase measurements. In fact, it has been shown that using kriging interpolation techniques, accurate refractivity maps within the coverage area of the radar can be obtained with high temporal resolution. In this paper, a detailed analysis of the time series of radar-based refractivity maps obtained during a dryline that occurred on the afternoon of 22 May 2002 during the International H2O Project (IHOP_2002) is presented. Comparisons between the time series of radar refractivity maps, obtained with the NCAR S-Pol radar, and the refractivity measurements derived from automatic ground-based weather stations and the AERI instrument, placed at different locations within the coverage area of the NCAR S-Pol radar, demonstrate the accuracy of radar refractivity estimates even for highly variable conditions, both in time and space, in the troposphere. Correlation coefficients higher than 0.95 are obtained in all weather station locations. Regarding the RMSE, errors less than 6 N-units are obtained for all cases, being even as low as 2.92 N-units at some locations.

Moth bean and tepary bean as green nitrogen sources in intensive winter wheat cropping systems

Use of cover crops have been suggested to increase agricultural sustainability by providing multiple ecosystems services. Replacing summer fallow with drought tolerant legumes could serve both as a cover and a green source of N for winter wheat (Triticum aestivum L.) and help mitigate economic and environmental problems by increasing resilience of agroecosystems in the United States (US) Southern Great Plains (SGP). Field experiments were conducted in 2018 and 2019 at the USDA - ARS Oklahoma and Central Plains Agricultural Research Center near El Reno, OK. The overall objective of the study was to quantify the potential of two summer legumes, tepary bean [Phaseolus acutifolius (A.) Gray] and moth bean [Vigna aconitifolia (Jacq.) Marechal], as green sources of N for winter wheat production in comparison with soybean [Glycine max (L.) Merr.]. The PROC MIXED procedure of the SAS statistical software was used to analyze biomass production by legumes, their impacts on soil water, soil N and yield of winter wheat, and N transfer from green N biomass to following winter wheat. Green N crops did not differ in biomass production, but soybean provided 22 % and 40 % more N than tepary bean and moth bean, respectively. Soil water was reduced under all green N crops than summer fallow at termination of green N crops and wheat planting. Biomass of green N crops increased N content in soils at wheat planting. Grain yield of winter wheat was significantly higher under tepary bean (5295 kg ha−1) than soybean (4300 kg ha−1), moth bean (4560 kg ha−1) and the control treatment (4323 kg ha−1). Nitrogen recovery in wheat biomass was greater under moth bean and tepary bean compared to soybean. Both moth bean and tepary bean could serve as green sources of N for winter wheat in the US SGP.

Climate change causes declines and greater extremes in wetland inundation in a region important for wetland birds.

Wetland ecosystems are vital for maintaining global biodiversity, as they provide important stopover sites for many species of migrating wetland-associated birds. However, because weather determines their hydrologic cycles, wetlands are highly vulnerable to effects of climate change. Although changes in temperature and precipitation resulting from climate change are expected to reduce inundation of wetlands, few efforts have been made to quantify how these changes will influence the availability of stopover sites for migratory wetland birds. Additionally, few studies have evaluated how climate change will influence interannual variability or the frequency of extremes in wetland availability. For spring and fall bird migration in seven ecoregions in the south-central Great Plains of North America, we developed predictive models associating abundance of inundated wetlands with a suite of weather and land cover variables. We then used these models to generate predictions of wetland inundation at the end of the century (2069-2099) under future climate change scenarios. Climate models predicted the average number of inundated wetlands will likely decline during both spring and fall migration periods, with declines being greatest in the eastern ecoregions of the southern Great Plains. However, the magnitude of predicted declines varied considerably across climate models and ecoregions, with uncertainty among climate models being greatest in the High Plains ecoregion. Most ecoregions also were predicted to experience more-frequent extremely dry years (i.e., years with extremely low wetland abundances), but the projected change in interannual variability of wetland inundation was relatively small and varied across ecoregions and seasons. Because the south-central Great Plains represents an important link along the migratory routes of many wetland-dependent avian species, future declines in wetland inundation and more frequent periods of only a few wetlands being inundated will result in an uncertain future for migratory birds as they experience reduced availability of wetland stopover habitat across their migration pathways.

Examining the vertical heterogeneity of aerosols over the Southern Great Plains

Abstract. Atmospheric aerosols affect the global energy budget by scattering and absorbing sunlight (direct effects) and by changing the microphysical structure, lifetime, and coverage of clouds (indirect effects). Both aerosol direct and indirect effects are affected by the vertical distribution of aerosols in the atmosphere, which is further influenced by a range of processes, such as aerosol dynamics, long-range transport, and entrainment. However, many observations of these processes are based on ground measurements, limiting our ability to understand the vertical distribution of aerosols and simulate their impact on clouds and climate. In this work, we examined the vertical heterogeneity of aerosols over the Atmospheric Radiation Measurement (ARM) Southern Great Plains (SGP) using data collected from the Holistic Interactions of Shallow Clouds, Aerosols and Land Ecosystems (HI-SCALE) campaign. The vertical profiles of meteorological and aerosol physiochemical properties up to 2500 m above are examined based on the 38 flights conducted during the HI-SCALE campaign. The aerosol properties over the SGP show strong vertical heterogeneity and seasonal variabilities. The aerosol concentrations at the surface are the highest due to strong emissions at ground level. In general, the mode diameter of aerosols during summer (∼ 100 nm) is larger than that during spring (∼ 30 nm), a result of enhanced condensational growth due to enriched volatile organic compounds in summer. The concentration of aerosols below 30 nm in the boundary layer (BL) (e.g., below 1000 m) during spring is higher than that during summer, a result of the stronger new particle formation (NPF) events due to the reduced condensation sink in spring. In the BL, the size of the aerosols gradually increases with altitude due to condensational growth and cloud processing. However, the chemical composition of the aerosols remained similar, with organics and sulfates representing 59.8 ± 2.2 % and 22.7 ± 2.1 %, respectively, of the total mass in the BL. Through the vertical profiles of aerosol properties, we observed NPF events in the upper BL during 7 out of 38 research flights, where the newly formed particles continue to grow as they are mixed down to the surface. There is also an indication that deep convection brings aerosols from the free troposphere (FT) to the surface, where they grow to contribute to the cloud condensation nuclei (CCN). Overall, the vertical heterogeneity of aerosols over the SGP is influenced by aerosol dynamics (new particle formation, growth, and cloud processing) and transport processes (mixing in the BL, long-range transport, entrainment, and convective downward transport). Case studies showing the influence of these factors are discussed.

Forage yield and nutritive value of summer legumes as affected by row spacing and harvest timing

Winter wheat (Triticum aestivum L.) is an essential, high-quality forage used for grazing stocker cattle from fall to spring in the US Southern Great Plains (SGP). However, the lack of nutritious forages during summers limits grazing by stocker cattle. To fill this quality gap, a short season species capable of producing significant yield and quality of forage is necessary. A two-year experiment was conducted to evaluate the performance of three legumes: tepary bean (Phaseolus acutifolius A. Gray), mothbean [Vigna aconitifolia (Jacq.) Marechal], and soybean [Glycine max (L.) Merr.] as a control, at different harvest dates, in response to different row spacing (38 ​cm and 76 ​cm) and moisture levels (rainfed and irrigated). Results showed forage yield by all legumes planted at 38 ​cm spacing (4.5 and 3.9 ​Mg ​ha−1) was higher than at 76 ​cm spacing (3.4 and 2.4 ​Mg ​ha−1) in 2018 and 2019. Soybean was the most productive while mothbean had the highest relative feed value (RFV) in both 2018 and 2019 (160 and 118, respectively). Although soybean produced more forage, mothbean and tepary bean provided high quality forage in terms of neutral detergent fiber (NDF), acid detergent fiber (ADF), and in-vitro true digestibility (IVTD). The results indicate that no single legume species stands out as the unequivocal leader in delivering both high-quality and abundant forage. Consequently, the choice of which species to utilize should be tailored to the specific forage requirements and management goals. Future research should explore mothbean genotypes to identify cultivars with greater yield potential and develop agronomic practices that effectively utilize those cultivars.

Effect of spatial and temporal “drought legacy” on dust sources in adjacent ecoregions

AbstractDrought affects the occurrence and intensity of aeolian dust events in many ecoregions. This study investigated the effects of “drought legacy” (the cumulative temporal persistence of drought's consequences on the earth system) on dust generation, a topic which had not previously been evaluated. We investigated the potential dust/drought legacy relationship in the USA's Southern Great Plains and Chihuahuan Desert ecoregions over 14 years, including the 2011–2012 extreme drought, at spatial distances up to 100 km around dust point sources and for up to 5 years' drought history. At every temporal and spatial scale, drought levels associated with dust initiation points in the two ecoregions were significantly different. Chihuahuan Desert dust sources concentrated in areas of severe to extreme drought, while those in the Southern Great Plains, which experiences greater land use, spanned wider ranges of drought conditions. At short temporal scales of drought (1 week and 1 year), dust initiation in the Chihuahuan Desert was associated strongly with severe to exceptional drought conditions at all spatial extents, while Southern Great Plains dust sources were linked to lower drought intensities. For longer drought histories (the past 2 and 5 years), Chihuahuan Desert dust sources were connected with moderate to severe drought, while Southern Great Plains dust sources were linked to moderate drought, at all spatial extents. Drought's legacies, extending over multiple years and kilometer scales, are shown to have roles in subsequent dust events at regional scales, though they can be regionally modulated by land use practices and ecosystem characteristics.

Interactions of long-term grazing and woody encroachment can shift soil biogeochemistry and microbiomes in savanna ecosystems

Semi-arid grasslands and savannas in the southern Great Plains USA are extensively used for livestock grazing. Over the past century, Juniperus (juniper) and Quercus (oak) species abundance have increased due to intensive grazing and reduced fire frequency. We investigated the interactions between livestock grazing history (none, moderate, heavy) and vegetation cover (grassland, juniper, oak) using a ∼ 70-year grazing experiment in west-central Texas. We explored effects on soil organic carbon (SOC), total nitrogen (TN), total phosphorus (TP), microbial community composition, and function. SOC and TN were 50–150 % higher under juniper and oak compared to grasslands, and 10–30 % lower in grazed vs. ungrazed areas. Vegetation × grazing interaction showed greater SOC and TN loss under oak than juniper or grasslands. Ungrazed controls had higher soil TP than grazed areas, with oak and juniper soils having more TP than grasslands. Bacterial and fungal communities differed between grassland and woody vegetation. Grazing affected only bacterial communities. SOC, TN, TP accounted for differences in community structure. Abundances of genes related to methane, nitrogen, sulfur metabolisms, and dominant fungal trophic modes were linked to soil C, N, P ratios. These findings highlight how long-term livestock grazing and woody plant encroachment influence soil C, N, P cycles, altering soil microbial community structure and function. This study provides insights for savanna ecosystem management and integrating land cover effects into biogeochemical models for global change scenarios.

Eastward shift in Juniperus virginiana distribution range under future climate conditions in the Southern Great Plains, United States

Eastern redcedar (Juniperus virginiana, redcedar) is a major woody species encroaching upon the native grasslands and forests of the southern Great Plains (SGP), representing a significant threat to regional ecosystem services. Future climate change is anticipated to influence redcedar habitat suitability, changing the probability of further encroachment and reshaping its spatial distribution. In this study, we trained seven Species Distribution Models (SDMs) with redcedar records from the USDA Forest Inventory Analysis database and used the ensemble of these SDMs to simulate redcedar distribution probability under current and future climate conditions in Kansas, Oklahoma, and Texas. Results reveal a distinct east-to-west gradient of decreasing distribution probability in the study domain, primarily driven by climate aridity. Throughout the 21st century, the optimal range of aridity for redcedar habitat is projected to shift eastwards by 0.7° (≈ 58 km) under the RCP45 climate scenario and 1.3° (≈ 108 km) under the RCP85. Accordingly, the suitable habitat will shift eastward by 0.6° (≈ 49 km) in the RCP45 and by 1.2° (≈ 103 km) in the RCP85. The proportion of unsuitable habitat will increase from 40.2 % of the study domain during 2000 – 2019 to 48 % in the RCP45 and 54.2 % in the RCP85 during 2080 – 2099. Additionally, highly suitable land areas will decrease from 10.4 % of the study domain during 2000 – 2019 to 1.3 % in the RCP45 and 0 % in the RCP85 by the end of this century. This study suggests a low likelihood of further redcedar encroachment in the west of the SGP states under future climates, while anticipating continued expansion in the east, gradually replacing the existing oak forests and rangelands. The findings provide valuable insights for prioritizing WPE management resources and contribute to our understanding of future changes in the SGP vegetation composition and their impacts on ecosystem dynamics.

Observations of Boundary Layer Convergence Lines and Associated Updrafts in the U.S. Southern Great Plains

Abstract Boundary layer convergence lines (CLs) are highly effective at deep-convection initiation (DCI), suggesting that their associated updraft properties differ from those of more widespread turbulent updrafts in the planetary boundary layer (PBL). This study exploits observations at the Atmospheric Radiation Measurement Southern Great Plains (ARM SGP) observatory in Oklahoma from 2011 to 2016 to quantify CL properties and their relation to turbulent PBL eddies preceding CL arrival. Two independent methods for estimating CL properties are developed at two locations in the SGP region, both relying on the assumption of a 2D circulation in the CL-normal plane but using different combinations of instruments. The first (the radar method) relies mainly on scanning radar data and is applied to 61 CLs passing near a high-resolution scanning radar based in Nardin, Oklahoma, while the second (the surface method) relies mainly on surface wind data and is applied to 68 CLs crossing the SGP facility in nearby Lamont, Oklahoma. Mean daytime (1000–1900 LST) CL width (∼2 km) and convergence magnitude (∼0.003 s−1) are similar for both methods, and mean daytime CL depth is ∼0.75 km. The two methods disagree at night (0000–1000 and 1900–2400 LST), where the surface method estimates wider and weaker CLs than the radar method. This difference may stem from the radar beam overshooting the shallow, highly stable nocturnal PBL. The largest CL updrafts are slightly wider (∼20%) and stronger (∼40%) than the largest PBL updrafts in the pre-CL period, generating 50%–100% larger updraft mass fluxes over most of the PBL depth. Significance Statement Deep convection is commonly initiated by boundary layer convergence lines (CLs), which are associated with intense surface-based wind convergence and strong updrafts that may lift air to saturation. Although CLs form regularly, they are far less common than ordinary, short-lived turbulent thermals in the daytime boundary layer. To better understand why CLs are so effective at deep-convection initiation, we observationally quantify their morphologies and strengths and compare these properties to those of surrounding turbulent updrafts. Perhaps surprisingly, the CLs are found to exhibit only slightly larger scales and strengths as the turbulent updrafts. Although these marginal increases help to explain the preference for storms to initiate along CLs, they likely are not the whole story.