Jeff Arnold

• Researcher at United States Department of Agriculture

Stream temperature is among the main drivers affecting water quality by influencing chemical reaction rates and biological activity. Due to globally rising air temperatures, increased stream temperatures are equally rising and becoming more relevant for ecosystem health. Stream temperature is influenced by a complex interplay of climate, hydrologic...

Nutrients such as nitrogen can be harmful to aquatic organisms in excessive amounts. Climate change, through possible increases in temperature and variable rainfall, may cause changes in nutrient loading patterns from watersheds. This study assesses the potential impact of climate and land use change on nitrate (NO3) loading in the Nanticoke River...

Coupled surface-subsurface hydrologic models are used worldwide to study historical patterns of water storage and hydrologic behaviour, investigate the impact of management strategies on water resources, and quantify the impact of changing climate, population, and policies. This study presents a new hydrologic model to simulate surface and subsurfa...

In the Mississippi alluvial plain (MAP) area, the demand for groundwater resources from the alluvial aquifer for agricultural irrigation has led to significant reductions in groundwater-level elevation over time. In this study, we use the hydrologic model SWAT + to quantify long-term changes in groundwater storage within the MAP in United States, w...

The accuracy of soil databases is essential in hydrological modeling, yet limited studies have evaluated the implications of using emerging soil datasets like POLARIS compared to traditional ones such as SSURGO. This study evaluates the performance of POLARIS soil data for simulating the streamflow and sediment yield at both the sub-basin and field...

Selenium (Se) is an essential micro-nutrient for humans and animals but can be toxic at high levels of intake. Quantifying the transport of Se in environmental systems is essential for understanding and mitigating Se contamination in soils, groundwater, and surface waters. In this study, we investigate the transport, storage, and contamination of S...

Study region: Lower Arkansas River Basin (LARB) in Colorado, USA. Study focus: The process of implementing irrigation in large river basins often results in significant changes in hydrologic pathways and fluxes, such as canal seepage, runoff, recharge, pumping, and groundwater-river exchange. The objective of this study is to quantify the hydrologi...

Global hydrological models are essential tools for understanding water resources and assessing climate change impacts at planetary scales, supporting water management, flood risk assessment, and sustainable development initiatives worldwide. The Soil and Water Assessment Tool (SWAT+) has demonstrated robust performance across various environments a...

Incorporating the simulation of water management actions in hydrological models is paramount to enhance their reliability and usefulness. SWAT + (Soil and Water Assessment Tool) includes novelties in this aspect compared to its previous versions: the decision tables and the water allocation module provide enhanced capabilities for configuring manag...

The Paraguay River Basin forms part of the La Plata River Basin in South America. Its streamflow is significantly attenuated by a high evapotranspiration rate, very gentle slopes and the presence of a vast wetland known as the Pantanal. Modeling the hydrology of watersheds in which the flood pulse is affected by the presence of large floodplains ca...

Distributed, coupled surface-groundwater hydrologic models are high-dimensional, given the necessity to reflect the spatially diverse nature of complex hydrologic processes. Furthermore, inverse/inference problems involving these high-dimensional models are naturally ill-posed, given the limited information content of state observations that are ty...

Societal risks from flooding are evident at a range of spatial scales and climate change will exacerbate these risks in the future. Assessing flood risks across broad geographical regions is a challenge, and often done using streamflow time-series records or hydrologic models. In this study, we used a national-scale hydrological model to identify,...

Floodplains are essential ecosystems that provide a variety of economic, hydrologic, and ecologic services. Within floodplains, surface water‐groundwater exchange plays an important role in facilitating biogeochemical processes and can have a strong influence on stream hydrology through infiltration or discharge of water. These functions can be dif...

Increasing precipitation accelerates soil erosion and boosts sediment loads, especially in mountain catchments. Therefore, there is significant pressure to deliver plausible assessments of these phenomena on a local scale under future climate change scenarios. Such assessments are primarily drawn from a combination of climate change projections and...

SWAT+ (Soil and Water Assessment Tool Plus), developed collaboratively by the USDA Agricultural Research Service (USDA-ARS), Texas A&M AgriLife Research (a part of The Texas A&M University System), Colorado State University, and the USDA-ARS Hydrology and Remote Sensing Laboratory, SWAT+ is a public domain model that empowers users to simulate wate...

We present a new calibration strategy guide for coupled surface-subsurface hydrologic models. The goal is to reduce bias in environmental modeling and make calibration processes more consistent. The strategy guide enhances model efficiency and accuracy by focusing on changes to channel, soil, landscape, and aquifer properties. This approach is part...

Irrigation practices and sources can have significant impacts on water resources and the hydrologic fluxes that control these resources. To better manage water resources and future water supply, the influence of irrigation practices and management on these hydrologic fluxes should be quantified in time and space at varying scales, under potential i...

Agricultural nutrient runoff has been a major contributor to hypoxia in many downstream coastal ecosystems. Although programs have been designed to reduce nutrient loading in individual coastal waters, cross watershed interdependencies of nutrient runoff have not been quantified due to a lack of suitable modeling tools. Cross-watershed pollution le...

Texas Gulf is one of the 18 regional sites that is part of the USDA‐ARS Long‐Term Agroecosystem Research (LTAR) network and focuses on cropland and integrated grazing land research in Central Texas, addressing challenges posed by soil characteristics, climate variability, and urbanization. This paper provides brief site descriptions of the two Crop...

Increasing precipitation accelerates soil erosion and boosts sediment loads, especially in mountain catchments. Therefore, there is significant pressure to deliver plausible assessments of these phenomena on a local scale under future climate change scenarios. Such assessments are primarily drawn from a combination of climate change projections and...

Parameter sensitivity analysis plays a critical role in efficiently determining main parameters, enhancing the effectiveness of the estimation of parameters and uncertainty quantification in hydrologic modeling. In this paper, we demonstrate an uncertainty and sensitivity analysis technique for the holistic Soil and Water Assessment Tool (SWAT+) mo...

Tile drainage is a common practice to increase agricultural productivity in regions with high water tables. Ecohydrological models, such as the Soil and Water Assessment Tool (SWAT), are key tools used to simulate these subsurface drainage structures and their corresponding management effects on water balance. This study is an investigation of the...

Groundwater saturation excess flow can be a major surface runoff mechanism in humid regions, characterized by shallow aquifers and soil profiles that become saturated during wet periods or intense storm events. This process often plays an important role in the creation and maintenance of groundwater-dependent ecosystems and the overall water yield...

CONTEXT Despite a steady increase in staple crop yields over the past ten years, current agricultural production must escalate even more to keep pace with the expected world population growth, which in turn will require improved agricultural methods that are adapted to many environmental pressures. Comprehensive models that can simulate crop produc...

Subsurface (or tile) drainage improves land productivity by enhancing soil aeration and preventing water-logged conditions. However, the continuous expansion of drained agricultural lands and reliance on synthetic fertilizer in the Midwestern United States have increasingly facilitated nitrate transport from agricultural fields to surface water bod...

Parameter Sensitivity analysis plays a critical role in efficiently determining main parameters, enhancing the effectiveness of estimation of parameters, and uncertainty quantification in hydrologic modeling. In this paper, we demonstrate uncertainty and sensitivity analysis technique for the holistic SWAT+ model, coupled with new gwflow module, sp...

Computer simulation models are a useful tool in planning, enabling reliable yet affordable what-if scenario analysis. Many simulation models have been proposed and used for urban planning and management. Still, there are a few modeling options available for the purpose of evaluating the effects of various stormwater control measures (SCM), includin...

We present an integrated hydrologic modeling approach for the conterminous United States using the SWAT + models of the National Agroecosystem Model (NAM). The NAM is a field-based, national scale hydrologic model to aid in conservation planning and policy. We augment the NAM by simulating groundwater storage and flow in a physically based spatiall...

Risks from flooding and poor water quality are evident at a range of spatial scales and climate change will exacerbate these risks in the future. Natural infrastructure (NI), consisting of structural or perennial vegetation, measures that provide multiple ecosystem benefits have the potential to reduce flood and water quality risks. In this study,...

The Soil and Water Assessment Tool (SWAT) is frequently used to simulate the transport of water-soluble chemicals in the environment such as pesticides and their metabolites originating from agricultural applications. However, the model does not simulate the transport of chemicals through subsurface tile drains and groundwater. This limitation is p...

Streambed aggradation and degradation are ways in which a stream will respond to changes in the incoming flow and sediment loads. Several environmental and societal problems are attributed to these channel bed adjustments. Prior studies have extensively used stream power to discern dominant channel processes and establish threshold limits required...

The streambed median grain size (D50) has been an integral part of many sediment transport and stream power equations seeking to characterize stream channel stability conditions. However, its previous usage is constrained by regional applicability, localization of datasets, and a limited number of data points. This study uses a large and geographic...

The Soil and Water Assessment Tool (SWAT) model is commonly used to predict the impacts of agricultural practices on water quality and quantity. Although widely applied, the data framework used to drive SWAT in the United States (U.S.) is fragmented and inconsistent, varying by user and model interface. This research describes the development of th...

The SWAT model is frequently used to simulate the transport of water-soluble chemicals in the environment such as pesticides and their metabolites originating from agricultural applications. However, the model does not simulate the transport of chemicals through subsurface tile drains and groundwater. This limitation is particularly significant in...

Nitrogen (N) fertilizer use in agricultural production is a significant determinant of surface water quality. As climate changes, agricultural producers are likely to adapt at extensive and intensive margins in terms of land and per acre input use, including fertilizers. These changes can affect downstream water quality. We investigate the effect o...

The latest version of the Soil and Water Assessment Tool (SWAT+) features several improvements compared to previous versions of the model, e.g. the definition of landscape units that allow for a better representation of spatio‐temporal dynamics. To evaluate the new model capabilities in lowland catchments characterized by near‐surface groundwater t...

The estimation of pesticide concentrations in surface water bodies with models is a critical component of the environmental and human health risk assessment process. The most recent version of the Soil and Water Assessment Tool (SWAT+) provides new features that are useful for pesticide exposure assessments. This research is the first SWAT+ pestici...

The Soil and Water Assessment Tool (SWAT) is an ecohydrological watershed-scale model which was initially developed in the early 1990s to simulate the impacts of land use, management systems, and climate on hydrology and/or water quality. First adopted in the U.S., the use of the model then spread to Europe and then later to Asia and other regions....

An integrated hydro-economic agricultural land use model was developed with endogenous and spatially explicit crop planting, nitrogen (N) fertilizer use and irrigation in the Mississippi River Basin (MRB). We used the model to quantify the effects of energy and N fertilizer prices on N runoff to the Gulf of Mexico. Results show a modest effect of e...

Extreme precipitation events are a major cause of economic damage and disruption, and need to be addressed for increasing resilience to a changing climate, particularly at the local scale. Practitioners typically want to understand local changes at spatial scales much smaller than the native resolution of most Global Climate Models, for which down...

Reflecting internal catchment hydrological processes in hydrological models is important for accurate predictions of the impact of climate and land‐use change on water resources. Characterizing these processes is however difficult and expensive due to their dynamic nature and spatio‐temporal variability. Hydropedology is a relatively new discipline...

LOADEST is a program for estimating constituent loads in rivers and streams developed by the U.S. Geological Survey (USGS), but it does not have a Graphical User Interface (GUI) that facilitates processing of large amounts of data. Therefore, we present the LOAD ESTimation (LOADEST) Parallel Data Processing Interface (LPDPI). LPDPI is unique as it...

There is a critical need for a national agroecosystem model for conservation policy and environmental planning, driven by issues including harmful algal blooms, water scarcity, flooding, and other weather‐related extremes. In this study, we illustrate the feasibility of a national agroecosystem model that will downscale processes to individual fiel...

Watershed models are used worldwide to assist with water and nutrient management under conditions of changing climate, land use, and population. Of these models, the Soil and Water Assessment Tool (SWAT) and SWAT+ are the most widely used, although their performance in groundwater-driven watersheds can sometimes be poor due to a simplistic represen...

Hydrologic modeling was used to estimate potential changes in nutrients, suspended sediment, and streamflow in various biomass production scenarios with conservation practices under different landscape designs. Two major corn and soybean croplands were selected for study: the South Fork of the Iowa River watershed and the headwater of the Raccoon R...

In this work, we developed a data-driven framework to predict near-surface (0-5 cm) soil moisture (SM) by mapping inputs from the Soil & Water Assessment Tool to SM time series from NASA's Soil Moisture Active Passive (SMAP) satellite for the period 1 January 2016-31 December 2018. We developed a hybrid artificial neural network (ANN) combining lon...

How anticipated climate change might affect long-term outcomes of present-day agricultural conservation practices remains a key uncertainty that could benefit water quality and biodiversity conservation planning. To explore this issue, we forecasted how the stream fish communities in the Western Lake Erie Basin (WLEB) would respond to increasing am...

• Many aquatic ecosystems are experiencing multiple anthropogenic stressors that threaten their ability to support ecologically and economically important fish species. Two of the most ubiquitous stressors are climate change and non‐point source nutrient pollution. • Agricultural conservation practices (ACPs, i.e. farming practices that reduce runo...

Accurate daily weather data are critical for hydrologic models simulating and predicting hydrologic processes. Many researchers have focused on the impacts of precipitation on hydrologic simulations, but few studies integrated both temperature and precipitation data for historical and forecast periods in hydrologic models and evaluated the weather...

This paper presents a version of SWAT + that uses MODFLOW to simulate groundwater flow and groundwater-surface interactions within a watershed system. The modeling code is applied to the 470 km² Middle Bosque River Watershed (Texas, USA) to demonstrate accuracy and differences with SWAT+. The model is tested against field-measured stream discharge,...

Soil moisture (SM) is a key component in water budgets and there is a well-documented need for near-real-time predictions for use is risk analyses including flooding and crop viability. Many well-known physics-based hydrologic models simulate and predict SM; however, they are structured to support calibration of streamflow discharges, not individua...

For almost 30 years, the Soil and Water Assessment Tool (SWAT) has been successfully implemented to address issues around various scientific subjects in the world. On the other hand, it has been reaching to the limit of potential flexibility in further development by the current structure. The new generation SWAT, dubbed SWAT+, was released recentl...

The Soil and Water Assessment Tool (SWAT) model is recognized as one of the top hydrological models applied for addressing hydrologic and environmental issues. This is the first review on the SWAT model studies in Southeast Asia, with an emphasis on its applications, current challenges and future research directions. A total of 126 articles were id...

Pesticide residue runoff to surface water is of great concern to local stakeholders who seek to preserve or achieve good water quality. The Soil & Water Assessment Tool (SWAT) has been widely used to assess many environmental problems related to water resources and nonpoint-source pollution, including sediment and nutrient loads and pesticides. How...

This study is a part of the Conservation Effects Assessment Project (CEAP) aimed to quantify the environmental and economic benefits of conservation practices implemented in the cultivated cropland throughout the United States. The Soil and Water Assessment Tool (SWAT) model under the Hydrologic United Modeling of the United States (HUMUS) framewor...

In recent years, watershed modelers have put increasing emphasis on capturing the interaction of landscape hydrologic processes instead of focusing on streamflow at the watershed outlet alone. Understanding the hydrologic connectivity between landscape elements is important to explain the hydrologic response of a watershed to rainfall events. The S...

Uncertainty in simulating hydrologic response to future climate is generally assumed to result from the combined uncertainties of the General Circulation Model (GCM), representative concentration pathway (RCP), downscaling method, and hydrologic model used. However, another source of uncertainty, the observed climate data source used to statistical...

The Des Moines Lobe (DML) of north-central Iowa has been artificially drained by subsurface drains and surface ditches to provide some of the most productive agricultural land in the world. Herein we report on the use of end-member mixing analysis (EMMA) models and the numerical model Soil and Water Assessment Tool (SWAT) to quantify the contributi...

The recent increase in global consumption of rice has led to increased demand for sustainable water management in paddy cultivation. In this study, we propose an enhanced paddy simulation module to be introduced to Soil and Water Assessment Tool (SWAT) to evaluate the sustainability of paddy cultivation. The enhancements added to SWAT include: (1)...

The recent increase in global consumption of rice has led to increased demand for sustainable water management in paddy cultivation. In this study, we propose an enhanced paddy simulation module to be introduced to Soil and Water Assessment Tool (SWAT) to evaluate the sustainability of paddy cultivation. The enhancements added to SWAT include: (1)...

Recent increase in global consumption of rice led to increased demand for sustainable water management in paddy cultivation. In this study, we propose an enhanced paddy simulation module in the SWAT model to evaluate sustainability of paddy cultivation. Enhancements added to SWAT are: 1) to modify water balance calculation for impounded fields, 2)...

A Richards-equation-based soil moisture module was developed and integrated within the Soil and Water Assessment Tool (SWAT). Four years of daily soil moisture measurements from 10 monitoring stations at three depths (i.e., 5, 10, and 50 cm) in the Choptank River watershed, Maryland, were used to test the module performance. Results show that, as c...

Quantifying Populus growth and the impacts on hydrology and water quality are important should it be widely planted. Soil and Water Assessment Tool (SWAT) tree growth algorithms and parameters for hybrid poplar in Midwestern US and cottonwood in Southern US were improved. Tree growth representation led to SWAT2012 code changes including a new leaf...

Vegetative filter strips (VFS) are popular conservation practices installed at the edges of agricultural fields to reduce losses of pollutants from agricultural areas to receiving waterbodies. The recent interest in using VFS areas as multifunctional landscapes necessitates an improved depiction of VFS in simulation models. This study is aimed to e...

Decision tables have been used for many years in data processing and business applications to simulate complex rule sets. Several computer languages have been developed based on rule systems and they are easily programmed in several current languages. Land management and river–reservoir models simulate complex land management operations and reservo...

Decision tables have been used for many years in data processing and business applications to simulate complex rule sets. Several computer languages have been developed based on rule systems and they are easily programmed in several current languages. Land management and river-reservoir models simulate complex land management operations and reservo...

Numerous studies have pointed out the importance of groundwater and surface water interaction (SW–GW) in a river system. However; those functions have rarely been considered in large scale hydrological models. The SWAT-LUD model has been developed based on the Soil and Water Assessment Tool (SWAT) model; and it integrates a new type of subbasin; wh...

Subsurface tile drainage systems are widely used in agricultural watersheds in the Midwestern US and enable the Midwest area to become highly productive agricultural lands, but can also create environmental problems, for example nitrate-N contamination associated with drainage waters. The Soil and Water Assessment Tool (SWAT) has been used to model...

Deep learning algorithms may be applied to create surrogate models for broadly applied hydrologic models, reducing computational time and inherent user biases to enhance real-time estimates used in risk evaluation scenarios. Remotely sensed parameters provide global, high resolution data sets with minimal data latency relative to in-situ observatio...

Model-based water quality assessments are an important informer of conservation and environmental policy in the U.S. The recently completed national scale Conservation Effects Assessment Project (CEAP) is being replicated using an improved model populated with new and higher resolution data. National assessments are particularly difficult as models...

The ability to accurately simulate flow and nutrient removal in treatment wetlands within an agricultural, watershed-scale model is needed to develop effective plans for meeting nutrient reduction goals associated with protection of drinking water supplies and reduction of the Gulf of Mexico hypoxic zone. The objectives of this study were to incorp...

Tile drainage significantly alters flow and nutrient pathways and reliable simulation at this scale is needed for effective planning of nutrient reduction strategies. The Soil and Water Assessment Tool (SWAT) has been widely utilized for prediction of flow and nutrient loads, but few applications have evaluated the model's ability to simulate pathw...

Large quantities of biofuel production are expected from bioenergy crops at a national scale to meet US biofuel goals. It is important to study biomass production of bioenergy crops and the impacts of these crops on water quantity and quality to identify environment-friendly and productive biofeedstock systems. SWAT2012 with a new tile drainage rou...

Gully erosion begins in streambanks and uplands as a consequence of adjustments in driving forces on the landscape imposed by changes in land use or climate. The deleterious effects of gullies worldwide have led to many site-specific studies of gully form and function. In the continental United States, gully erosion in agricultural land has destroy...

Water quality simulation models such as the Soil and Water Assessment Tool (SWAT) and Agricultural Policy EXtender (APEX) are widely used in the US. These models require large amounts of spatial and tabular data to simulate the natural world. Accurate and seamless daily climatic data are critical for accurate depiction of the hydrologic cycle, yet...

Hydrologic modeling outputs are influenced by how a watershed system is represented. Channel routing is a typical example of the mathematical conceptualization of watershed landscape and processes in hydrologic modeling. We investigated the sensitivity of accuracy, equifinality, and uncertainty of Soil and Water Assessment Tool (SWAT) modeling to c...

The proper representation of conservation practices on agricultural lands is an important factor in large scale assessments of water quality in the US. Unfortunately, there are few publicly available data sources at the local level and even fewer at the national scale. In this research, randomly selected points within agricultural lands were examin...

Rangelands of the Pampa biome, which cover regions of Argentina, Uruguay and Brazil (176,496 km² – 2.07% of Brazilian territory and 63% of Rio Grande do Sul State territory, southern region of Brazil) in South America (total area of 750,000 km²), are being substituted by crops and commercial eucalyptus, with potential impacts on ecological and hydr...

Accurate discharge simulation is one of the most common objectives of hydrological modeling studies. However, a good simulation of discharge is not necessarily the result of a realistic simulation of hydrological processes within the catchment. We propose an evaluation framework that considers both discharge and water balance components as evaluati...