Anthony D. Kendall

Improved methods for satellite‐based groundwater storage estimates: A decade of monitoring the high plains aquifer from space and ground observations

The impacts of climate extremes and water use on groundwater storage across large aquifers can be quantified using Gravity Recovery and Climate Experiment (GRACE) satellite monitoring. We present new methods to improve estimates of changes in groundwater storage by incorporating irrigation soil moisture corrections to common data assimilation products. These methods are demonstrated using data from the High Plains Aquifer (HPA) for 2003 to 2013. Accounting for the impacts of observed and inferred irrigation on soil moisture significantly improves estimates of groundwater storage changes as verified by interpolated measurements from ~10,000 HPA wells. The resulting estimates show persistent declines in groundwater storage across the HPA, more severe in the southern and central HPA than in the north. Groundwater levels declined by an average of approximately 276 ± 23 mm from 2003 to 2013, resulting in a storage loss of 125 ± 4.3 km3, based on the most accurate of the three methods developed here.

Water Level Declines in the High Plains Aquifer: Predevelopment to Resource Senescence.

A large imbalance between recharge and water withdrawal has caused vital regions of the High Plains Aquifer (HPA) to experience significant declines in storage. A new predevelopment map coupled with a synthesis of annual water levels demonstrates that aquifer storage has declined by approximately 410 km(3) since the 1930s, a 15% larger decline than previous estimates. If current rates of decline continue, much of the Southern High Plains and parts of the Central High Plains will have insufficient water for irrigation within the next 20 to 30 years, whereas most of the Northern High Plains will experience little change in storage. In the western parts of the Central and northern part of the Southern High Plains, saturated thickness has locally declined by more than 50%, and is currently declining at rates of 10% to 20% of initial thickness per decade. The most agriculturally productive portions of the High Plains will not support irrigated production within a matter of decades without significant changes in management.

Linking fecal bacteria in rivers to landscape, geochemical, and hydrologic factors and sources at the basin scale

Significance New microbial source-tracking tools can be used to elucidate important nonpoint sources of water quality degradation and potential human health risks at large scales. Pollution arising from septic system discharges is likely more important than previously realized. Identifying these sources and providing reference levels for water quality provides a basis to assess water quality trends and ultimately remediate degraded areas. Linking fecal indicator bacteria concentrations in large mixed-use watersheds back to diffuse human sources, such as septic systems, has met limited success. In this study, 64 rivers that drain 84% of Michigan’s Lower Peninsula were sampled under baseflow conditions for Escherichia coli, Bacteroides thetaiotaomicron (a human source-tracking marker), landscape characteristics, and geochemical and hydrologic variables. E. coli and B. thetaiotaomicron were routinely detected in sampled rivers and an E. coli reference level was defined (1.4 log10 most probable number⋅100 mL−1). Using classification and regression tree analysis and demographic estimates of wastewater treatments per watershed, septic systems seem to be the primary driver of fecal bacteria levels. In particular, watersheds with more than 1,621 septic systems exhibited significantly higher concentrations of B. thetaiotaomicron. This information is vital for evaluating water quality and health implications, determining the impacts of septic systems on watersheds, and improving management decisions for locating, constructing, and maintaining on-site wastewater treatment systems.

Effects of Irrigation on Summer Precipitation over the United States

AbstractIrrigation’s effects on precipitation during an exceptionally dry summer (June–August 2012) in the United States were quantified by incorporating a novel dynamic irrigation scheme into the Weather Research and Forecasting (WRF) Model. The scheme is designed to represent a typical application strategy for farmlands across the conterminous United States (CONUS) and a satellite-derived irrigation map was incorporated into the WRF-Noah-Mosaic module to realistically trigger the irrigation. Results show that this new irrigation approach can dynamically generate irrigation water amounts that are in close agreement with the actual irrigation water amounts across the high plains (HP), where the prescribed scheme best matches real-world irrigation practices. Surface energy and water budgets have been substantially altered by irrigation, leading to modified large-scale atmospheric circulations. In the studied dry summer, irrigation was found to strengthen the dominant interior high pressure system over the ...

The future of agriculture over the Ogallala Aquifer: Solutions to grow crops more efficiently with limited water

We explore the unsustainable path that the Ogallala region faces, and provide some suggestions for policies that would extend the usable lifespan of the water in the aquifer, which supports the vast majority of the economy across this region. We emphasize the critical role of science as a foundation for policies that can help mitigate the disaster that is occurring across the region and provide insights because we believe that there are solutions to some aspects of this water crisis. Summary In some areas of the HPA, farmers can no longer pump enough water for crops. Water-use efficiency and farmers profitability can be significantly enhanced by adopting site-specific agronomic management identified by coupling precision agricultural technologies with crop models. Policies grounded in science are critical to ensure long-term sustainability.

Can impacts of climate change and agricultural adaptation strategies be accurately quantified if crop models are annually re-initialized?

Estimates of climate change impacts on global food production are generally based on statistical or process-based models. Process-based models can provide robust predictions of agricultural yield responses to changing climate and management. However, applications of these models often suffer from bias due to the common practice of re-initializing soil conditions to the same state for each year of the forecast period. If simulations neglect to include year-to-year changes in initial soil conditions and water content related to agronomic management, adaptation and mitigation strategies designed to maintain stable yields under climate change cannot be properly evaluated. We apply a process-based crop system model that avoids re-initialization bias to demonstrate the importance of simulating both year-to-year and cumulative changes in pre-season soil carbon, nutrient, and water availability. Results are contrasted with simulations using annual re-initialization, and differences are striking. We then demonstrate the potential for the most likely adaptation strategy to offset climate change impacts on yields using continuous simulations through the end of the 21st century. Simulations that annually re-initialize pre-season soil carbon and water contents introduce an inappropriate yield bias that obscures the potential for agricultural management to ameliorate the deleterious effects of rising temperatures and greater rainfall variability.

The Origin and Physical Properties of the Cometary Knots in NGC 7293

On the basis that the cometary knots observed in the Helix Nebula form as a result of larger parent clouds breaking up due to Rayleigh-Taylor instability induced by radiative acceleration of the clouds, we compute characteristics of the cometary knots and of the parent clouds as well. Present observations place constraints on the positions, velocities, and sizes of the parent clouds. Requiring the clouds to produce cometary knots that are stable places further constraints on the properties of parent clouds. We formulate those constraints and show how they further limit the predicted properties of the cometary knots and bring them into agreement with their observed properties.

A Method for Estimating Wall Friction in Turbulent Boundary Layers

We describe a simple method for estimating wall fricti on which uses the fit of velocity data to the boundary layer profile in wall units all the way from the wall to the end of the log region. Two different models for the boundary layer profile are examined, the power -series interpolation scheme of Spalding a nd the Musker profile which is based on the eddy viscosity concept. The accuracy of the new method is quantified using the zero pressure gradient 2 -D turbulent boundary layer data of Osterlund for which independent measurement of wall shear is available. Results show that the new procedure can provide accurate estimates of wall shear with a mean error of about two percent or better. The usefulness of this method is in its ability to provide accurate estimates of wall shear not only based on full velocity profile data but also sparse data points in the velocity profile, including only a single data point.

Complex water management in modern agriculture: Trends in the water-energy-food nexus over the High Plains Aquifer.

In modern agriculture, the interplay between complex physical, agricultural, and socioeconomic water use drivers must be fully understood to successfully manage water supplies on extended timescales. This is particularly evident across large portions of the High Plains Aquifer where groundwater levels have declined at unsustainable rates despite improvements in both the efficiency of water use and water productivity in agricultural practices. Improved technology and land use practices have not mitigated groundwater level declines, thus water management strategies must adapt accordingly or risk further resource loss. In this study, we analyze the water-energy-food nexus over the High Plains Aquifer as a framework to isolate the major drivers that have shaped the history, and will direct the future, of water use in modern agriculture. Based on this analysis, we conclude that future water management strategies can benefit from: (1) prioritizing farmer profit to encourage decision-making that aligns with strategic objectives, (2) management of water as both an input into the water-energy-food nexus and a key incentive for farmers, (3) adaptive frameworks that allow for short-term objectives within long-term goals, (4) innovative strategies that fit within restrictive political frameworks, (5) reduced production risks to aid farmer decision-making, and (6) increasing the political desire to conserve valuable water resources. This research sets the foundation to address water management as a function of complex decision-making trends linked to the water-energy-food nexus. Water management strategy recommendations are made based on the objective of balancing farmer profit and conserving water resources to ensure future agricultural production.

Groundwater depletion and climate change: future prospects of crop production in the Central High Plains Aquifer

Crop production in the Central High Plains is at an all-time high due to increased demand for biofuels, food, and animal products. Despite the need to produce more food by mid-century to meet expected population growth, under current management and genetics, crop production is likely to plateau or decline in the Central High Plains due to groundwater withdrawal at rates that greatly exceed recharge to the aquifer. The Central High Plains has experienced a consistent decline in groundwater storage due to groundwater withdrawal for irrigation greatly exceeding natural recharge. In this heavily irrigated region, water is essential to maintain yields and economic stability. Here, we evaluate how current trends in irrigation demand may impact groundwater depletion and quantify the impacts of these changes on crop yield and production through to 2099 using the well-established System Approach to Land Use Sustainability (SALUS) crop model. The results show that status quo groundwater management will likely reduce irrigated corn acreage by ~60% and wheat acreage by ~50%. This widespread forced shift to dryland farming, coupled with the likely effects of climate change, will contribute to overall changes in crop production. Taking into account both changes in yield and available irrigated acreage, corn production would decrease by approximately 60%, while production of wheat would remain fairly steady with a slight increase of about 2%.