Physical Sciences and Mathematics Commons^™

Building An Improved Drought Climatology Using Updated Drought Tools: A New Mexico Food-Energy-Water (Few) Systems Focus, Lindsay E. Johnson, Hatim M.E. Geli, Michael J. Hayes, Kelly Helm Smith

Drought Mitigation Center: Faculty Publications

Drought is a familiar climatic phenomenon in the United States Southwest, with complex human-environment interactions that extend beyond just the physical drought events. Due to continued climate variability and change, droughts are expected to become more frequent and/or severe in the future. Decision-makers are charged with mitigating and adapting to these more extreme conditions and to do that they need to understand the specific impacts drought has on regional and local scales, and how these impacts compare to historical conditions. Tremendous progress in drought monitoring strategies has occurred over the past several decades, with more tools providing greater spatial and …

Impacts Of Environmental Conditions On Fleas In Black-Tailed Prairie Dog Burrows, Julia E. Poje, Tonie Rocke, Michael D. Samuel

United States Geological Survey: Staff Publications

Sylvatic plague, caused by the bacterium Yersinia pestis and transmitted by fleas, occurs in prairie dogs of the western United States. Outbreaks can devastate prairie dog communities, often causing nearly 100% mortality. Three competent flea vectors, prairie dog specialists Oropsylla hirsuta and O. tuberculata, and generalist Pulex simulans, are found on prairie dogs and in their burrows. Fleas are affected by climate, which varies across the range of black-tailed prairie dogs (Cynomys ludovicianus), but these effects may be ameliorated somewhat due to the burrowing habits of prairie dogs. Our goal was to assess how temperature and precipitation …

Forest Drought Response Index (Fordri): A New Combined Model To Monitor Forest Drought In The Eastern United States, Tsegaye Tadesse, David Y. Hollinger, Yared A. Bayissa, Mark Svoboda, Brian Fuchs, Beichen Zhang, Getachew Demissie, Brian D. Wardlow, Gil Bohrer, Kenneth L. Clark, Ankur R. Desai, Lianhong Gu, Asko Noormets, Kimberly A. Novick, Andrew D. Richardson

Drought Mitigation Center: Faculty Publications

Monitoring drought impacts in forest ecosystems is a complex process because forest ecosystems are composed of different species with heterogeneous structural compositions. Even though forest drought status is a key control on the carbon cycle, very few indices exist to monitor and predict forest drought stress. The Forest Drought Indicator (ForDRI) is a new monitoring tool developed by the National Drought Mitigation Center (NDMC) to identify forest drought stress. ForDRI integrates 12 types of data, including satellite, climate, evaporative demand, ground water, and soil moisture, into a single hybrid index to estimate tree stress. The model uses Principal Component Analysis …

Seasonal Grassland Productivity Forecast For The U.S. Great Plains Using Grass-Cast, Melannie D. Hartman, William J. Parton, Justin D. Derner, Darin K. Schulte, William K. Smith, Dannele E. Peck, Ken A. Day, Stephen J. Del Grosso, Susan Lutz, Brian Fuchs, Maosi Chen, Wei Gao

Drought Mitigation Center: Faculty Publications

Every spring, ranchers in the drought-prone U.S. Great Plains face the same difficult challenge —trying to estimate how much forage will be available for livestock to graze during the upcoming summer grazing season. To reduce this uncertainty in predicting forage availability, we developed an innovative new grassland productivity forecast system, named Grass-Cast, to provide science-informed estimates of growing season aboveground net primary production (ANPP). Grass-Cast uses over 30 yr of historical data including weather and the satellite-derived normalized vegetation difference index (NDVI)—combined with ecosystem modeling and seasonal precipitation forecasts—to predict if rangelands in individual counties are likely to produce below-normal, …

Anthropogenic Change On The Distribution Of Marine Megafauna And Their Prey, Baylie Fadool

Honors Theses

Anthropogenic change is impacting the distribution and survival of marine megafauna and their prey. Humans are changing every aspect of the marine environment, with effects reaching as large as changing the composition of marine environments to directly overexploiting species through the fishing industry. The role that marine megafauna play in balancing ecosystems, including as top apex predators, leads to detrimental results in the absences and population declines of these species. Migrations and declines due to threats on marine apex predator species will alter their environments by causing mesopredator release and changes in community structure, which is often associated with reduced …

A Detailed Assessment Of Groundwater Quality In The Kabul Basin, Afghanistan, And Suitability For Future Development, Hussain Ali Jawadi, Jay Sagin, Daniel D. Snow

Nebraska Water Center: Faculty Publications

Abstract: Kabul is one of the most populated cities in Afghanistan and providing resources to support this population in an arid climate presents a serious environmental challenge. The current study evaluated the quality of local Kabul Basin groundwater to determine its suitability water for drinking and irrigation purposes now and into the future. This aim was aided through groundwater parameter assessment as well as determination ofWater Quality Index (WQI) developed from 15 observation points near the city. The results of our physicochemical analysis illustrate that groundwater in the majority of areas of the Kabul Basin is not generally suitable for …

A Detailed Assessment Of Groundwater Quality In The Kabul Basin, Afghanistan, And Suitability For Future Development, Hussain Ali Jawadi, Jay Sagin, Daniel D. Snow

Nebraska Water Center: Faculty Publications

Kabul is one of the most populated cities in Afghanistan and providing resources to support this population in an arid climate presents a serious environmental challenge. The current study evaluated the quality of local Kabul Basin groundwater to determine its suitability water for drinking and irrigation purposes now and into the future. This aim was aided through groundwater parameter assessment as well as determination ofWater Quality Index (WQI) developed from 15 observation points near the city. The results of our physicochemical analysis illustrate that groundwater in the majority of areas of the Kabul Basin is not generally suitable for human …

Implementation Of An Occupancy-Based Monitoring Protocol For A Widespread And Cryptic Species, The New England Cottontail (Sylvilagus Transitionalis), Colin P. Shea, Mitchell J. Eaton, Darryl I. Mackenzie

United States Geological Survey: Staff Publications

Context. Designing effective long-term monitoring strategies is essential for managing wildlife populations. Implementing a cost-effective, practical monitoring program is especially challenging for widespread but locally rare species. Early successional habitat preferred by the New England cottontail (NEC) has become increasingly rare and fragmented, resulting in substantial declines from their peak distribution in the mid-1900s. The introduction of a possible competitor species, the eastern cottontail (EC),may also have played a role. Uncertainty surrounding how these factors have contributed to NEC declines has complicated management and necessitated development of an appropriate monitoring framework to understand possible drivers of distribution and dynamics.

Aims. …

Calibrating Human Attention As Indicator: Monitoring #Drought In The Twittersphere, Kelly Smith, Andrew Tyre, Zhenghong Tang, Michael Hayes, Adnan Akyuz

Drought Mitigation Center: Faculty Publications

State climatologists and other expert drought observers have speculated about the value of monitoring Twitter for #drought and related hashtags. This study statistically examines the relationships between the rate of tweeting using #drought and related hashtags, within states, accounting for drought status and news coverage of drought. We collected and geolocated tweets, 2017–18, and used regression analysis and a diversity statistic to explain expected and identify unexpected volumes of tweets. This provides a quantifiable means to detect state-weeks with a volume of tweets that exceeds the upper limit of the prediction interval. To filter out instances where a high volume …

Repetitive Sampling And Control Threshold Improve 16s Rrna Gene Sequencing Results From Produced Waters Associated With Hydraulically Fractured Shale, Jenna L. Shelton, Elliott P. Barnhart, Leslie Ruppert, Aaron M. Jubb, Madalyn S. Blondes, Christina A. Devera

United States Geological Survey: Staff Publications

Sequencing microbial DNA from deep subsurface environments is complicated by a number of issues ranging from contamination to non-reproducible results. Many samples obtained from these environments – which are of great interest due to the potential to stimulate microbial methane generation – contain low biomass. Therefore, samples from these environments are difficult to study as sequencing results can be easily impacted by contamination. In this case, the low amount of sample biomass may be effectively swamped by the contaminating DNA and generate misleading results. Additionally, performing field work in these environments can be difficult, as researchers generally have limited access …

Heat Stored In The Earth System: Where Does The Energy Go?, Karina Von Schuckmann, Lijing Cheng, Matthew D. Palmer, James Hansen, Caterina Tassone, Valentin Aich, Susheel Adusumilli, Hugo Beltrami, Tim Boyer, Francisco José Cuesta-Valero, Damien Desbruyères, Catia Domingues, Almudena García-García, Pierre Gentine, John Gilson, Maximillian Gorfer, Leopold Haimberger, Masayoshi Ishii, Gregory C. Johnson, Rachel Killick, Brian A. King, Gottfried Kirchengast, Nicolas Kolodziejczyk, John Lyman, Ben Marzeion, Michael Mayer, Maeva Monier, Didier Paolo Monselesan, Sarah Purkey, Dean Roemmich, Axel Schweiger, Sonia I. Seneviratne, Andrew Shepherd, Donald A. Slater, Andrea K. Steiner, Fiammetta Straneo, Mary-Louise Timmermans, Susan E. Wijffels

United States Department of Commerce: Staff Publications

Human-induced atmospheric composition changes cause a radiative imbalance at the top of the atmosphere which is driving global warming. This Earth energy imbalance (EEI) is the most critical number defining the prospects for continued global warming and climate change. Understanding the heat gain of the Earth system—and particularly how much and where the heat is distributed—is fundamental to understanding how this affects warming ocean, atmosphere and land; rising surface temperature; sea level; and loss of grounded and floating ice, which are fundamental concerns for society. This study is a Global Climate Observing System (GCOS) concerted international effort to update the …

Evaluating Airsoft Electric Guns For Control Of Invasive Brown Treesnakes, Adam J. Knox, Björn Lardner, Amy Yackel Adams, Robert N. Reed

United States Geological Survey: Staff Publications

Firearms are often used in lethal control of invasive vertebrates, but safety and regulatory aspects limit the circumstances under which they can be used. During August 2016 at the Brown Treesnake Project laboratory on Guam, we evaluated hobby‐grade Airsoft Electric Guns (AEGs; a lower powered, less‐hazardous, and less‐regulated alternative to firearms) for capture and control of small animals, with specific emphasis on invasive brown treesnakes (Boiga irregularis). Tests of AEGs differing in power with ammunition (plastic pellets) masses ranging from 0.20 to 0.39 g, fired at gelatin blocks from distances of 4, 8, and 12 m, showed that …

Development And Performance Assessment Of An Integrated Vermifiltration Based Treatment System For The Treatment Of Feedlot Runoff, Rajneesh Singh, Matteo D'Alessio, Yulie Meneses, Shannon L. Bartelt-Hunt, Brian Woodbury, Chittaranjan Ray

Nebraska Water Center: Faculty Publications

The objective of this study was to treat feedlot runoff by developing an ecologically sustainable, affordable, and resilient treatment system having a relatively long life span. Three horizontal flow soil biofilters were utilized in this study: 1) without earthworms and plants (Biofilter (BF)), 2) with earthworms only (Vermifilter (VF)), and 3) with earthworms and plants (Macrophyte Assisted Vermifilter (MAVF)). The experiments were conducted with a hydraulic retention time of four days using Lumbricus terestrris earthworms and Carex frankii wetland plants. The average COD removal from the BF, VF, and MAVF were 23.2–30.4%, 61.4–69.1%, and 68.3–78.1%, respectively. Average TN removal efficiencies …

Using Climate To Explain And Predict West Nile Virus Risk In Nebraska, Kelly Helm Smith, Andrew J. Tyre, Jeff Hamik, Michael J. Hayes, Yuzhen Zhou, Li Dai

Drought Mitigation Center: Faculty Publications

We used monthly precipitation and temperature data to give early warning of years with higher West Nile Virus (WNV) risk in Nebraska. We used generalized additive models with a negative binomial distribution and smoothing curves to identify combinations of extremes and timing that had the most influence, experimenting with all combinations of temperature and drought data, lagged by 12, 18, 24, 30, and 36 months. We fit models on data from 2002 through 2011, used Akaike's Information Criterion (AIC) to select the best‐fitting model, and used 2012 as out‐of‐sample data for prediction, and repeated this process for each successive year, …

Climate Change And Market-Based Insurance Feedbacks, Eric R. Holley, Adam Liska, Cory Walters, Geoffrey C. Friesen, Michael Hayes, Max J. Rudolph, Donald A. Wilhite

Adam Liska Papers

Climatic events have accounted for 91% of $1.05 trillion in insured costs for global catastrophic events from 1980 to 2016. Costs are driven by socio-economic development and increased frequency and severity of climatic disasters driven by climate change. Government policies to reduce systemic risk (e.g., cap-and-trade, carbon tax) have been a predominant approach for mitigation and adaptation. Alternatively, market-based incentives for climate change adaptation and mitigation already operate via the insurance industry to lessen impacts on society. Insurance feedbacks include changes in 1) premiums and insurance policies, 2) non-coverage, and 3) policy making and litigation. Alongside government policies, insurance feedbacks …

Statement Of World Aquatic Scientific Societies On The Need To Take Urgent Action Against Human-Caused Climate Change, Based On Scientific Evidence [Dear Colleague Letter], Scott A. Bonar, Brian R. Murphy, Leanne H. Roulson, Jesse T. Trushenski, Douglas J. Austen, Michael Edward Douglas

United States Fish and Wildlife: Staff Publications

Dear Colleague Letter from the American Fisheries Society to fellow scientific societies, July 25, 2020, about the urgent need for responsive collective action to mitigate impending radical climate change. Includes the Statement of World Aquatic Scientific Societies on the Need to Take Urgent Action Against Human-Caused Climate Change, Based on Scientific Evidence, emphasizing the importance of aquatic ecosystems. Includes extensive citations and notes.

"Water is the most important natural resource on Earth as it is vital for life. Aquatic ecosystems, freshwater or marine, provide multiple benefits to human society, such as provisioning of oxygen, food, drinking water, genetic resources; regulation …

Legacy And Current Pesticide Residues In Syr Darya, Kazakhstan: Contamination Status, Seasonal Variation And Preliminary Ecological Risk Assessment, Daniel D. Snow, P. Chakraborty, B. Uralbekov, B. Satybaldiev, J. Brett Sallach, L. M. Thornton Hampton, M. Jeffries, A. S. Kolok, Shannon L. Bartelt-Hunt

Nebraska Water Center: Faculty Publications

The Syr Darya is one of two major rivers in Central Asia supplying critical fresh water to the Aral Sea. In spite of the river’s importance and agriculturally-intensive history, few studies have provided a modern evaluation of and the occurrence of pesticide residues potential effects to aquatic life. The primary goal of this investigation was to determine seasonal variations in ambient concentrations of modern and legacy pesticides in bottom sediment and water of the Syr Darya in Kazakhstan (KZ) downstream from an agriculturally-intensive watershed in Uzbekistan. Grab samples and passive samplers were used at five remote sampling stations during June …

Monitoring Residual Soil Moisture And Its Association To The Long-Term Variability Of Rainfall Over The Upper Blue Nile Basin In Ethiopia, Getachew Ayehu, Tsegaye Tadesse, Berhan Gessesse

Drought Mitigation Center: Faculty Publications

Monitoring soil moisture and its association with rainfall variability is important to comprehend the hydrological processes and to set proper agricultural water use management to maximize crop growth and productivity. In this study, the European Space Agency’s Climate Change Initiative (ESA CCI) soil moisture product was applied to assess the dynamics of residual soil moisture in autumn (September to November) and its response to the long-term variability of rainfall in the Upper Blue Nile Basin (UBNB) of Ethiopia from 1992 to 2017. The basin was found to have autumn soil moisture (ASM) ranging from 0.09–0.38 m³/m³, …

Climate Change Impacts The Subsurface Transport Of Atrazine And Estrone Originating From Agricultural Production Activities, Renys Enrique Barrios, Simin Akbariyeh, Chuyang Liu, Khalid Muzamil Gani, Margarita T. Kovalchuk, Xu Li, Yusong Li, Daniel D. Snow, Zhenghong Tang, John Gates, Shannon L. Bartelt-Hunt

Nebraska Water Center: Faculty Publications

Climate change will impact soil properties such as soil moisture, organic carbon and temperature and changes in these properties will influence the sorption, biodegradation and leaching of trace organic contaminants to groundwater. In this study, we conducted a modeling case study to evaluate atrazine and estrone transport in the subsurface under current and future climate conditions at a field site in central Nebraska. According to the modeling results, in the future, enhanced evapotranspiration and increased average air temperature may cause drier soil conditions, which consequently reduces the biodegradation of atrazine and estrone in the water phase. On the other hand, …

Vertebrates On The Brink As Indicators Of Biological Annihilation And The Sixth Mass Extinction, Gerardo Ceballos, Paul R. Ehrlich, Peter H. Raven

Harold W. Manter Laboratory: Library Materials

The ongoing sixth mass species extinction is the result of the destruction of component populations leading to eventual extirpation of entire species. Populations and species extinctions have severe implications for society through the degradation of ecosystem services. Here we assess the extinction crisis from a different perspective. We examine 29,400 species of terrestrial vertebrates, and determine which are on the brink of extinction because they have fewer than 1,000 individuals. There are 515 species on the brink (1.7% of the evaluated vertebrates). Around 94% of the populations of 77 mammal and bird species on the brink have been lost in …

Combined Use Of Sentinel‐1 Sar And Landsat Sensors Products For Residual Soil Moisture Retrieval Over Agricultural Fields In The Upper Blue Nile Basin, Ethiopia, Getachew Ayehu, Tsegaye Tadesse, Berhan Gessesse, Yibeltal Yigrem, Assefa M. Melesse

Drought Mitigation Center: Faculty Publications

The objective of this paper is to investigate the potential of sentinel‐1 SAR sensor products and the contribution of soil roughness parameters to estimate volumetric residual soil moisture (RSM) in the Upper Blue Nile (UBN) basin, Ethiopia. The backscatter contribution of crop residue water content was estimated using Landsat sensor product and the water cloud model (WCM). The surface roughness parameters were estimated from the Oh and Baghdadi models. A feed‐forward artificial neural network (ANN) method was tested for its potential to translate SAR backscattering and surface roughness input variables to RSM values. The model was trained for three inversion …

A Hydrometeorological Assessment Of The Historic 2019 Flood Of Nebraska, Iowa, And South Dakota, Paul Xavier Flanagan, Rezaul Mahmood, Natalie Umphlett, Erin M.K. Haacker, Chittaranjan Ray, Bill Sorensen, Martha Shulski, Crystal J. Stiles, David Pearson, Paul Fajman

HPRCC Personnel Publications

During early 2019, a series of events set the stage for devastating floods in eastern Nebraska, western Iowa, and southeastern South Dakota. When the floodwaters hit, dams and levees failed, cutting off towns, while destroying roads, bridges, and rail lines, further exacerbating the crisis. Lives were lost and thousands of cattle were stranded. Estimates indicate that the cost of the flooding has topped $3 billion as of August 2019, with this number expected to rise.

After a warm and wet start to winter, eastern Nebraska, western Iowa, and southeastern South Dakota endured anomalously low temperatures and record-breaking snowfall. By March …

What Is The U.S. Drought Monitor?, National Drought Mitigation Center

National Drought Mitigation Center: Publications

The USDA uses the map as a trigger for programs that help agricultural producers recover from drought and other natural disasters:

Livestock Forage Disaster Program (LFP)

Emergency Assistance for Livestock, Honeybees, and Farm Raised Fish Program (ELAP)

Fast-Track Secretarial Disaster Declarations

Emergency Loans Program

The U.S. Drought Monitor Network: Improving Drought Early Warning, The U.S. Drought Monitor Network

National Drought Mitigation Center: Publications

WHAT IS THE U.S. DROUGHT MONITOR NETWORK?

WHO ARE THE OBSERVERS?

WHAT BENEFITS?

The network in action

HOW DOES IT WORK?

WHO CREATES THE MAP?

What Is The Limiting Nutrient In Winter In Urban Reservoirs? A Case Study., Precious Nyabami

Department of Earth and Atmospheric Sciences: Dissertations, Theses, and Student Research

The importance of reservoirs in widely acknowledged by urban population, yet little is understood scientifically about their ability to process nutrients deposited into them in winter. Nutrients in waste water, lawns and construction runoff are deposited into reservoirs and several ecosystem services are lost which leads to what several researchers call “the urban syndrome”. Some studies have been done on the winter limnology of lakes, yet little is understood about the same process in reservoirs. To fill this missing knowledge gap, a study on one of Nebraska’s lakes (Holmes’ lake) was done. In this study, we simulated how phosphorus, nitrogen …

Building Adaptive Capacity In Tribal Communities Of The Missouri River Basin To Manage Drought And Climate Extremes: A Case Study From The Wind River Indian Reservation, Crystal J. Stiles, Natalie Umphlett, Mitch Cottenoir

HPRCC Personnel Publications

Native American peoples of the Northern and Central Plains have long endured harsh climate conditions, such as floods and droughts, and they possess valuable traditional knowledges that have enhanced their resilience to these extreme events. However, in recent times, limited capacity to adapt to a rapidly changing climate combined with a lack of resources have increased tribes’ vulnerability to climate extremes and their associated impacts. In response, a number of projects have been developed to assist tribes with their self-identified climate- and drought-related needs, particularly in the context of on-reservation decision-making. In this case study, we present an engagement strategy …

Adjusting The Lens Of Invasion Biology To Focus On The Impacts Of Climate-Driven Range Shifts, Piper D. Wallingford, Toni Lyn Morelli, Jenica M. Allen, Evelyn M. Beaury, Dana M. Blumenthal, Bethany A. Bradley, Jeffrey S. Dukes, Regan Early, Emily J. Fusco, Deborah E. Goldberg, Inés Ibáñez, Brittany B. Laginhas, Montserrat Vilà, Cascade J.B. Sorte

United States Geological Survey: Staff Publications

As Earth’s climate rapidly changes, species range shifts are considered key to species persistence. However, some range-shifting species will alter community structure and ecosystem processes. By adapting existing invasion risk assessment frameworks, we can identify characteristics shared with high-impact introductions and thus predict potential impacts. There are fundamental differences between introduced and range-shifting species, primarily shared evolutionary histories between range shifters and their new community. Nevertheless, impacts can occur via analogous mechanisms, such as wide dispersal, community disturbance and low biotic resistance. As ranges shift in response to climate change, we have an opportunity to develop plans to facilitate advantageous …

Increased Drought Severity Tracks Warming In The United States’ Largest River Basin, Justin T. Martin, Gregory T. Pederson, Connie A. Woodhouse, Edward R. Cook, Gregory J. Mccabe, Kevin J. Anchukaitis, Erika K. Wise, Patrick J. Erger, Larry Dolan, Marketa Mcguire, Subhrendu Gangopadhyay, Katherine J. Chase, Jeremy S. Litell, Stephen T. Gray, Scott St. George, Jonathan M. Friedman, David J. Sauchyn, Jeannine-Marie St-Jacques, John King

United States Geological Survey: Staff Publications

Across the Upper Missouri River Basin, the recent drought of 2000 to 2010, known as the “turn-of-the-century drought,” was likely more severe than any in the instrumental record including the Dust Bowl drought. However, until now, adequate proxy records needed to better understand this event with regard to long-term variability have been lacking. Here we examine 1,200 y of streamflow from a network of 17 new tree-ring–based reconstructions for gages across the upper Missouri basin and an independent reconstruction of warm-season regional temperature in order to place the recent drought in a long-term climate context. We find that temperature has …

Case Studies Of Colorado Lows And The Impacts On Winter Weather Maintenance, Nathan Rick

Department of Earth and Atmospheric Sciences: Dissertations, Theses, and Student Research

Winter storms of varying degrees plague the Plains each year, bringing with them ice, snow, wind, and cold temperatures which adversely affect public, commercial, and private transportation alike. The Nebraska Department of Transportation (NDOT) adopted a Maintenance Decision Support System (NDOT-MDSS) to aid in their winter weather maintenance practices. NDOT-MDSS ingests data from a variety of numerical weather models as well as real time surface and pavement observations to output both a weather forecast and winter road maintenance recommendation that can be taken into account by NDOT to finalize their maintenance decisions for a specific storm system or road segment. …

A Polarimetric Radar Analysis Of Cold- And Warm-Based Supercells, Timothy J. Gunkel

Department of Earth and Atmospheric Sciences: Dissertations, Theses, and Student Research

Polarimetric analyses of supercell thunderstorms have been increasingly common within the past decade, since operational polarimetric radar data became available in 2013. Although polarimetric signatures within supercell thunderstorms are well known, few have investigated variability in these signatures in differing environments. Polarimetric signatures can provide vital information regarding the microphysical characteristics and processes in supercell thunderstorms. Specific polarimetric signatures of interest are the differential reflectivity (Z_DR) column, the low-level polarimetrically inferred hail core, and the Z_DR arc. These signatures provide information regarding updraft characteristics, hailfall characteristics, and size sorting processes in the storm- relative inflow. Previous studies …