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Synopsis Robustness and resilience are widely used in the biological sciences and related disciplines to describe how systems respond to change. Robustness is the ability to tolerate change without adapting or moving to another state. Resilience refers to the ability for a system to sustain a perturbation and maintain critical functions. Robustness and resilience transcend levels of biological organization, though they do not scale directly across levels. We live in an era of novel stressors and unprecedented change, including climate change, emerging environmental contaminants, and changes to the Earth's biogeochemical and hydrological cycles. We envision a common framework for developing models to predict the robustness and resilience of biological functions associated with complex systems that can transcend disciplinary boundaries. Conceptual and quantitative models of robustness and resilience must consider cross-scale interactions of potentially infinite complexity, but it is impossible to capture everything within a single model. Here, we discuss the need to balance accuracy and complexity when designing models, data collection, and downstream analyses to study robustness and resilience. We also consider the difficulties in defining the spatiotemporal domain when studying robustness and resilience as an emergent property of a complex system. We suggest a framework for implementing transdisciplinary research on robustness and resilience of biological systems that draws on participatory stakeholder engagement methods from the fields of conservation and natural resources management. Further, we suggest that a common, simplified model development framework for describing complex biological systems will provide new, broadly relevant educational tools. Efficient interdisciplinary collaboration to accurately develop a model of robustness and resilience would enable rapid, context-specific assessment of complex biological systems with benefits for a broad range of societally relevant problems.

Vibrio cholera, the bacteria that cause cholera, is endemic in Haiti with a presence in both cities and remote areas. Improved access to drinking water testing and treatment in remote areas may reduce the impact of the disease. This case study uses correlation and regression analysis to identify the main factors that hinder access to water testing and that lead to high cholera infection rates among communities in the Northern Corridor of Haiti. Poor road conditions, mountainous terrain, and limited transportation options lead to high travel times up to 5.7 min/km between remote communities and drinking water testing facilities. The presence of springs in a community has a significant positive correlation with cholera infection rates in the Northern Corridor. However, socioeconomic factors had no significant correlation with cholera infection rate. The results of this study will be used to plan the implementation of a new drinking water testing laboratory near the city of Cap-Haitian and other programs for vulnerable remote areas. PRACTITIONER POINTS: Topography and road conditions may be more important than distance in determining the accessibility of water testing facilities for rural communities. A lack of access to private vehicles is a substantial challenge for many rural communities in accessing water testing. The presence of springs in a community had a significant positive correlation with cholera infection rate.

To address issues created by increased stormwater runoff, there is growing interest in sustainable tools such as permeable pavement (PP), which is a green infrastructure (GI) practice. This paper outlines the development and application of a design tool called the “cost optimization tool for permeable pavements (COTPP).” This tool aims to help states, municipalities, and consultants design PPs using reliable hydrological and structural pavement design methods. The COTPP uses a cost optimization algorithm similar to a heuristic search that helps identify which combination of PPs, conventional pavement, and other GIs provides the most economic value. A sensitivity analysis was conducted using the tool, which consisted of designing the three main types of PP using varying design inputs and comparing the COTPP’s results to results from an existing design tool or guidelines. The average percent differences between the COTPP’s results and that of other methods were below 10% for the structural designs and around 15% for the hydrological designs. The differences were caused by the use of a safety factor in the hydrological design and other adjustments to design methods. It was concluded that the tool is reliable and can be confidently used by designers. The tool was then used for a representative case study site (PP parking lot) in which the actual design and cost estimates of on-site components were known. The COTPP was able to identify other design alternatives that helped reduce the actual construction cost of the existing parking lot from $305,918 to as low as $238,790.

Green infrastructure (GI) practices are an effective means for improving the sustainability of stormwater management. Optimized combinations of GI practices with other management practices,...

Due to land development, high concentrations of suspended sediment are produced from erosion after rain events. Sediment basins are commonly used for the settlement of suspended sediments before discharge. Stormwater regulations may require frequent sampling and monitoring of these basins, both of which are time and labor intensive. Potential remedies are small, unoccupied aerial systems (sUAS). The goal of this study was to demonstrate whether sUAS multispectral imagery could measure high levels of total suspended solids (TSS) and turbidity in a sediment basin. The sediment basin at the Auburn University Erosion and Sediment Control Testing Facility was used to simulate a local 2-year, 24-h storm event with a 30-min flow rate. Water samples were collected at three depths in two locations every 15 min for six hours with corresponding sUAS multispectral imagery. Multispectral pixel values were related to TSS and turbidity in separate models using multiple linear regressions. TSS and turbidity regression models had coefficients of determination (r2) values of 0.926 and 0.851, respectively. When water column measurements were averaged, the r2 values increased to 0.965 and 0.929, respectively. The results indicated that sUAS multispectral imagery is a viable option for monitoring and assessing sediment basins during high-concentration events. Published version

The mountainous regions of the southern United States experience substantial snow loads. This study develops a data-driven method for determining 50-year ground snow load (GSL) in high-ele...

Climate change and wildfire are interacting to drive vegetation change and potentially reduce water quantity and quality in the southwestern United States, Forest restoration is a management approach that could mitigate some of these negative outcomes. However, little information exists on how restoration combined with climate change might influence hydrology across large forest landscapes that incorporate multiple vegetation types and complex fire regimes. We combined spatially explicit vegetation and fire modeling with statistical water and sediment yield models for a large forested landscape (335,000 ha) on the Kaibab Plateau in northern Arizona, USA. Our objective was to assess the impacts of climate change and forest restoration on the future fire regime, forest vegetation, and watershed outputs. Our model results predict that the combination of climate change and high-severity fire will drive forest turnover, biomass declines, and compositional change in future forests. Restoration treatments may reduce the area burned in high-severity fires and reduce conversions from forested to non-forested conditions. Even though mid-elevation forests are the targets of restoration, the treatments are expected to delay the decline of high-elevation spruce-fir, aspen, and mixed conifer forests by reducing the occurrence of high-severity fires that may spread across ecoregions. We estimate that climate-induced vegetation changes will result in annual runoff declines of up to 10%, while restoration reduced or reversed this decline. The hydrologic model suggests that mid-elevation forests, which are the targets of restoration treatments, provide around 80% of runoff in this system and the conservation of mid- to high-elevation forests types provides the greatest benefit in terms of water conservation. We also predict that restoration treatments will conserve water quality by reducing patches of high-severity fire that are associated with high sediment yield. Restoration treatments are a management strategy that may reduce undesirable outcomes for multiple ecosystem services.

Urbanization is increasing rapidly and has the potential to alter the hydrologic cycle. It is uncertain if hydrologic alteration metrics developed for large-scale analyses detect the impacts of urbanization. This study tests the ability of two such methods, Indicators of Hydrologic Alteration (IHA) and streamflow signatures, to detect the effects of urbanization in two watersheds in the southeastern U.S.A. A hydrologic model (HEC-HMS) was used to simulate flows in ungauged upstream tributaries to determine if analysis of flow from a large gauged watershed detects urbanization effects on upstream tributaries. IHA analysis detected trends in time in the watersheds, but the results were the opposite of what would be expected as urbanization increased minimum flows, decreased maximum flows, and decreased flashiness based on the trend in time and comparison with an undeveloped watershed. IHA parameters were more sensitive to urbanization than streamflow signatures. Subcatchments that transitioned from low to moderate or high levels of urbanization had greater levels of hydrologic alteration than was detected at the watershed outlet. Analyses of stream gauge network data may underestimate the importance of urbanization as a watershed characteristic due to scale issues, the variable effects of water management, and the dynamic nature of urbanization.

Open science practices such as publishing data and code are transforming water science by enabling synthesis and enhancing reproducibility. However, as research increasingly bridges the physical and social science domains (e.g., socio?hydrology), there is the potential for well?meaning researchers to unintentionally violate the privacy and security of individuals or communities by sharing sensitive information. Here, we identify the contexts in which privacy violations are most likely to occur, such as working with high?resolution spatial data (e.g., from remote sensing), consumer data (e.g., from smart meters), and/or digital trace data (e.g., from social media). We also suggest practices for identifying and addressing privacy concerns at the individual, institutional, and disciplinary levels. We strongly advocate that the water science community continue moving toward open science and socio?environmental research and that progress toward these goals be rooted in open and ethical data management., by Udit Bhatia et al.

Snow provides a key water source for stream flow and agricultural production across western North America and drinking water for large populations in the Southwest. Accurate estimates of snow cover spatial distribution and temporal dynamics are important at regional and local scales as snow cover is projected to decrease due to global climate change. We examined regional-scale temporal trends in snow distribution across central and northern Arizona using two tiles of 2928 daily images of MOD10 snow product. The analysis included the entire MODIS archive time period, October 1, 2003–June 1, 2014, and a 245,041 km2 area of 51 HUC8 watersheds. We also examined the effects of a regional forest restoration effort, known as the Four Forest Restoration Initiative (4FRI), aimed at enhancing snow accumulation and retention for increased groundwater recharge through forest thinning and burning treatments. We analyzed 66 Landsat TM/ETM + images spanning 26 years between 1988 and 2014 at five sites and one hyperspectral image from 2014 at two sites. The MOD10 snow product performs well in estimating Arizona's thin and discontinuous snow distribution. Mann-Kendall time-series analysis indicate significantly increasing trends in the annual number of snow cover days (SCD) over the 12-year period in 1.6% of the region at elevation transitions such as the Mogollon Rim in central Arizona, while significantly decreasing trends are observed at a few locations of lower elevations leading to the desert margins in eastern Arizona. The observed temporal trends are mostly consistent with ground-based SNOTEL snow measurements. An Arizona specific, Landsat sensor-derived binary classification model, similar to the MOD10 product, was developed at a local scale. It performs better than commonly-used simple threshold-based approaches, but demonstrates the continued challenges associated with Landsat sensor-derived snow classification in Arizona likely due to its coarse temporal resolution. Landsat-derived multi-temporal Normalized Difference Snow Index (NDSI) analysis indicate that treated (thinned and thinned-and-burned) forest sites had significantly greater NDSI values than untreated control sites. Snowpack at treated sites also appeared to persist longer into the spring season with potentially greater contributions to groundwater recharge in this semi-arid region. The high-resolution hyperspectral data analysis indicate that sites treated to approximately 24% forest canopy cover appear to have an optimum threshold for accumulating and maintaining snowpack. It balances canopy cover versus canopy gap, which reduces snow interception and sublimation by canopy, while providing enough shade. These results are encouraging for the 4FRI, the first and largest forest restoration effort in the US history, aimed at improving watershed health and function in the face of changing climate.

Evapotranspiration (ET) is a major component of the water budget in most forests, in many cases exceeding 70% of annual precipitation. Due to limitations in time and resources, input data necessary to model ET are not always available for a study site, but offsite data from meteorological networks may be a suitable substitute. In this study, we evaluated three models for estimating ET, Priestly-Taylor (P-T), Shuttleworth-Wallace (S-W), and Penman-Monteith with dynamic stomatal resistance (P-M-d), in a ponderosa pine (Pinus ponderosa) forest in northern Arizona where eddy covariance data exist for comparison. We tested the sensitivity of the models to the use of offsite meteorological data from a weather station and offsite soil moisture data from two snow monitoring sites in the SNOTEL network. Onsite data are required for accurate ET estimation with the P-M-d model because of its complexity. Acceptable accuracy in ET estimation required onsite net radiation data for the P-T model and onsite vapor pressure deficit data for the S-W model; other input data can be obtained from nearby offsite weather stations. Errors in ET estimation produced by the use of offsite soil moisture data varied between two nearby SNOTEL sites. Recommendations about the use of offsite data are presented.

Forest thinning has been used as a management tool to reverse the adverse impacts of decades of fire suppression in the western USA. Research into the impacts of thinning on surface water, soil, and vegetation re-growth have occurred concurrently with the growing popularity of forest thinning; however, its potential impact on groundwater recharge and related springs ecosystems has largely been ignored until recently. This systematic review provides an overview of some of the tools used to measure the influence of forest management on groundwater recharge, including numerical and process based modeling, empirical paired-watershed approaches, and statistical stochastic techniques. A brief discussion of the benefits and drawbacks of each method also is provided. The paper provides a literature review of existing studies of groundwater recharge and forest management from 1971 to 2018. The review of 35 studies indicates a range of results and highlights differences between studies of clear-cut forests versus thinned forests. Forests that were thinned had a greater amount of groundwater recharge than clear-cut forests, indicating that recharge responds positively and more strongly to reduced sublimation and evaporation in partially thinned forests than to clear-cut removal of mature trees. A similar test with forest encroachment studies revealed no differences between forest encroachment and either thinning regime. The number of forest management-groundwater recharge studies has dramatically increased over the last two decades, indicating increased interest in finding tools to increase groundwater yields for societal use in rapidly populating aridland forests. To our knowledge there have been no studies of forest thinning impacts on springs ecosystems, a field of study rich with possibilities for ecologists, hydrologists, rangeland and forestry scientists, and interdisciplinary ecohydrology practitioners.

Evapotranspiration (ET) comprises a major portion of the water budget in forests, yet few studies have measured or estimated ET in semi-arid, high-elevation ponderosa pine forests of the south-western USA or have investigated the capacity of models to predict ET in disturbed forests. We measured actual ET with the eddy covariance (eddy) method over 4 years in three ponderosa pine forests near Flagstaff, Arizona, that differ in disturbance history (undisturbed control, wildfire burned, and restoration thinning) and compared these measurements (415–510 mm year−1 on average) with actual ET estimated from five meteorological models [Penman–Monteith (P-M), P-M with dynamic control of stomatal resistance (P-M-d), Priestley–Taylor (P-T), McNaughton–Black (M-B), and Shuttleworth–Wallace (S-W)] and from the Moderate Resolution Imaging Spectroradiometer (MODIS) ET product. The meteorological models with constant stomatal resistance (P-M, M-B, and S-W) provided the most accurate estimates of annual eddy ET (average percent differences ranged between 11 and −14%), but their accuracy varied across sites. The P-M-d consistently underpredicted ET at all sites. The more simplistic P-T model performed well at the control site (18% overprediction) but strongly overpredicted annual eddy ET at the restoration sites (92%) and underpredicted at the fire site (−26%). The MODIS ET underpredicted annual eddy ET at all sites by at least 51% primarily because of underestimation of leaf area index. Overall, we conclude that with accurate parameterization, micrometeorological models can predict ET within 30% in forests of the south-western USA and that remote sensing-based ET estimates need to be improved through use of higher resolution products. Copyright © 2014 John Wiley & Sons, Ltd.

The purpose of this study was to develop an interpretive groundwater-flow model to assess the impacts that planned forest restoration treatments and anticipated climate change will have on large regional, deep (>400 m), semi-arid aquifers. Simulations were conducted to examine how tree basal area reductions impact groundwater recharge from historic conditions to 2099. Novel spatial analyses were conducted to determine areas and rates of potential increases in groundwater recharge. Changes in recharge were applied to the model by identifying zones of basal area reduction from planned forest restoration treatments and applying recharge-change factors to these zones. Over a 10-year period of forest restoration treatment, a 2.8% increase in recharge to one adjacent groundwater basin (the Verde Valley sub-basin) was estimated, compared to conditions that existed from 2000 to 2005. However, this increase in recharge was assumed to quickly decline after treatment due to regrowth of vegetation and forest underbrush and their associated increased evapotranspiration. Furthermore, simulated increases in groundwater recharge were masked by decreases in water levels, stream baseflow, and groundwater storage resulting from surface water diversions and groundwater pumping. These results indicate that there is an imbalance between water supply and demand in this regional, semi-arid aquifer. Current water management practices may not be sustainable into the far future and comprehensive action should be taken to minimize this water budget imbalance.

Savannah ecosystems are important carbon stocks on the Earth, and their quantification is crucial for understanding the global impact of climate and land-use changes in savannahs. The estimation of aboveground/belowground plant biomass requires tested allometric relationships that can be used to determine total plant biomass as a function of easy-to-measure morphological indicators. Despite recent advances in savannah ecology, research on allometric relations in savannahs remains confined to a few site-specific studies where basal area is typically used as the main morphometric parameter with plant biomass. We investigate allometric relations at four sites along a 950-km transect in the Kalahari across mean rainfall gradient 170 mm yr-1-550 mm yr-1. Using data from 342 harvested trees/shrubs, we relate basal area, height and crown diameter to aboveground biomass. These relationships are strongest in trees and weakest in small shrubs. Strong allometric relationships are also determined for morphologically similar groups of woody vegetation. We show that crown diameter can be used as an alternative to basal area in allometric relationships with plant biomass. This finding may enhance the ability to determine aboveground biomass over large areas using high-resolution aerial or satellite imagery without requiring ground-based measurements of basal area. © 2013 John Wiley & Sons Ltd.

The impact of human activity on the biophysical world raises myriad challenges for sustaining earth system processes, ecosystem services, and human societies. To engage in meaningful problem-solving in the hydrosphere, this necessitates an approach that recognizes the coupled nature of human and biophysical systems. We argue that in order to produce the next generation of problem-solvers, hydrology education should ensure that students develop an appreciation and working familiarity in the context of coupled human-environmental systems. We illustrate how undergraduate-level hydrology assignments can extend beyond rote computations or basic throughput scenarios to include consideration of the dynamic interactions with social and other biophysical dimensions of complex adaptive systems. Such an educational approach not only builds appropriate breadth of dynamic understanding, but can also empower students toward assuming influential and effective roles in solving sustainability challenges.

The connectivity of ecohydrological and biogeochemical processes across time and space is a critical determinant of ecosystem structure and function. However, characterizing cross-scale connectivity is a challenge due to the lack of theories and modelling approaches that are applicable at multiple scales and due to our rudimentary understanding of the magnitude and dynamics of such connectivity. In this article, we present a conceptual framework for upscaling quantitative models of ecohydrological and biogeochemical processes using electrical circuit analogies and the Thevenin's theorem. Any process with a feasible linear electrical circuit analogy can be represented in larger scale models as a simplified Thevenin equivalent. The Thevenin equivalent behaves identically to the original circuit, so the mechanistic features of the model are maintained at larger scales. We present three case applications: water transport, carbon transport, and nitrogen transport. These examples show that Thevenin's theorem could be a useful tool for upscaling models of interconnected ecohydrological and biogeochemical systems. It is also possible to investigate how disruptions in micro-scale connectivity can affect macro-scale processes. The utility of the Thevenin's theorem in environmental sciences is somewhat limited, because not all processes can be represented as linear electrical circuits. However, where it is applicable, it provides an inherently scalable and quantitative framework for describing ecohydrological connectivity. Copyright © 2010 John Wiley & Sons, Ltd.

[1] The conversion of grasslands to shrublands by woody plant encroachment is a common occurrence in arid and semi-arid regions that can have significant effects on ecosystem hydrology and biogeochemistry, including changes in soil organic carbon stocks. The mechanisms determining the direction and magnitude of soil carbon change due to encroachment are unknown but appear to depend on factors that vary along a gradient of mean annual precipitation. We present a model of coupled steady-state soil moisture and carbon dynamics that accounts for the effects of structural heterogeneity at the scale of vegetation patches by representing the local effects of root systems and canopies. We applied the model to paired grasslands and woody encroachment-produced shrublands spanning a climate gradient in the American Southwest, and model results were consistent with measured values. Modeled transpiration, which was used to determine productivity, was 5%–57% greater in shrublands, with the greatest difference occurring where the relative difference in leaf area index between grass and shrub patches was small and vegetation density was low. Patterns of soil carbon abundance were mainly driven by patterns of productivity, but decomposition rates were also affected by vegetation structure. Woody encroachment increases heterogeneity in soil carbon decomposition rates and has the net effect of increasing soil carbon residence times by 3.6–4.9 years. Our model represents an important step toward a mechanistic and quantitative understanding of the effect of vegetation structure on soil moisture and carbon dynamics and highlights the need for a better description of belowground vegetation structure in ecosystem models.

The contribution of savannas to global carbon storage is poorly understood, in part due to lack of knowledge of the amount of belowground biomass. In these ecosystems, the coexistence of woody and herbaceous life forms is often explained on the basis of belowground interactions among roots. However, the distribution of root biomass in savannas has seldom been investigated, and the dependence of root biomass on rainfall regime remains unclear, particularly for woody plants. Here we investigate patterns of belowground woody biomass along a rainfall gradient in the Kalahari of southern Africa, a region with consistent sandy soils. We test the hypotheses that (1) the root depth increases with mean annual precipitation (root optimality and plant hydrotropism hypothesis), and (2) the root-to-shoot ratio increases with decreasing mean annual rainfall (functional equilibrium hypothesis). Both hypotheses have been previously assessed for herbaceous vegetation using global root data sets. Our data do not support these hypotheses for the case of woody plants in savannas. We find that in the Kalahari, the root profiles of woody plants do not become deeper with increasing mean annual precipitation, whereas the root-to-shoot ratios decrease along a gradient of increasing aridity.

The relative importance of resource competition and disturbance in limiting woody cover is one of the most basic questions in savanna ecology. Modeling approaches that seek to address this question are limited in their ability to accurately represent resource competition, which occurs belowground, by the limited detail of existing data on root system structure. Using compressed air, we excavated individual trees and shrubs and mapped their coarse roots on a three-dimensional grid system up to 1.5 m depth. We excavated four woody savanna species at three sites spanning a climate gradient on the Kalahari Transect in southern Africa and determined functions to describe the distribution of root biomass within the root systems. Overall, most of the variation in both large-scale and small-scale characteristics of root system structure was related to species. The species excavated fell into two groups that coexisted across the climate gradient. Acacia mellifera and Terminalia sericea had straight roots in a laterally extensive system that was shallow relative to the aggregate root profile for woody plants at the sites. Boscia albitrunca and Ochna pulchra had sinuous roots that were mostly concentrated beneath the canopy and were more prevalent in deep than near-surface soil layers, departing from the conventional model of decreasing root abundance with depth. Based on our results, we suggest a reframing of the theoretical characterization of the root zone used in modeling approaches to consider diversity within the woody plant community.