Measurements of biophysical tree properties and hydrologic fluxes are necessary for improving models and monitoring the impact of disturbances. Prior research has demonstrated that measurements of tree sway frequency can be used to quantify important ecohydrologic processes, such as drought stress and snow interception, that otherwise require expensive measurement techniques. However, existing instruments used to measure tree sway lack spatial scalability. We investigate whether the virtual vision sensor and multilevel binary thresholding video processing algorithms can be used to accurately extract tree sway frequency at multiple points in a video camera field of view and enable scalable measurements of ecohydrologic processes. Comparing sway frequencies extracted from video and accelerometer data at two sites, we show that for 30-60 s videos, the video processing algorithms can reproduce accelerometer sway frequencies with ±0.03 Hz accuracy. The results suggest that video processing algorithms may be suitable for applications where changes in sway frequency are on the order of tenths of hertz or larger, for example the measurement of snow in trees. Further work is needed to clarify the accuracy of the algorithms when applied to longer videos, which may be required to monitor processes with more subtle changes in sway frequency, such as diurnal changes in tree water content.

Stream and riverbed sediments are hot spots for coupled transport and biogeochemical processes at the aquatic-terrestrial interface. The influx of fresh, metabolically labile particulate organic matter (POM) into the near-surface riverbed plays a critical role in fueling microbial activity in the hyporheic zone. Despite the importance of POM in driving biogeochemical reactions, key questions remain about the physical transport of POM under transient and reversable flow conditions. This study examined the transport of fresh periphyton-derived photosynthetic biomass in laboratory columns containing sandy porous sediment from the Hanford Reach of the Columbia River. Breakthrough (BT) experiments at different fluid flow velocities, with and without reversals in flow direction, were used to assess the processes controlling POM transport. Although the timing of initial POM breakthrough was the same as the conservative tracer, extensive retention (ca. 60-80 %) of photosynthetic biomass was observed. Filtration coefficients (ca. 0.05-0.08 cm-1) did not vary systematically with fluid flow velocity. The experiments demonstrated significant tailing on the falling limb of BT curves. Transport-reaction modeling indicated that these results could be explained by a combination of particle filtration and rate-limited attachment/detachment of colloids to/from the sediment matrix. Flow reversal experiments examined the potential impact of flow direction change on POM remobilization, a common but previously unquantified and unmodeled phenomenon. Significant remobilization of POM took place during flow reversal following initial POM influx, creating a pulse of suspended POM outflow above the initial input concentration. Incorporation of a first-order remobilization process into the transport-reaction model was able to reproduce pulses of remobilized POM associated with multiple flow reversals. The results of this study shed light on the interplay between river water-hyporheic zone fluid exchange and the direction/intensity of fresh POM transport in the near-surface riverbed.

This study deals with the riverbed of the Columbia river in the vicinity of the Hanford 300 Area study site in eastern Washington, where fluctuations in river stage take place both naturally (i.e. seasonally) and in conjunction with hydroelectric power dam operations. These fluctuations create conditions conducive to the influx and transport of fine-grained POM (a biological colloid originating from the river water and/or in situ periphyton production), within near-surface riverbed sediments. Although a great deal is known about dissolved organic matter (DOM) transport and metabolism in hyporheic zone sediments, there is a paucity of quantitative information on POM dynamics and its influence on hyporheic zone biogeochemistry (e.g. dissolved oxygen dynamics). We have developed a hydrobiogeochemical model capable of simulating the transport and metabolism of POM and its impact on dissolved oxygen (DO) distribution within the riverbed as influenced by periodic changes in river stage and fluid flow rate and direction. The model was employed as a tool to interpret the results of in situ measurements of POM intrusion into the riverbed made using “POM traps” emplaced within the upper 20 cm of the riverbed, as well as real-time in situ dissolved oxygen concentrations determined with a novel optical sensor buried directly in the riverbed at 20 cm depth. The simulations reproduced the accumulation of fresh POM within the upper few 5 cm of the riverbed observed in field POM trap deployments. Once sufficient surface POM accumulation takes place, an underlying zone of DO depletion develops as a consequence of variation in the rate of fluid exchange and POM/DOM degradation. The model predicted cyclic, hydrologically-driven variations in near-surface DO that are consistent with the results of the in situ DO probe deployments together with parallel measurements of fluid conductivity and hydrologic pressure. Our results suggest a complex interplay between fluid flow rate/direction and DO distribution that has important implication for riverbed biogeochemical dynamics at a variety of scales, as influenced by hydrological variability as well as the relative intensity of POM input and the availability of oxygen and other electron acceptors for microbial metabolism.

Urbanization substantially modifies surface water and energy cycles. Compared to natural vegetation, paved urban surfaces produce more runoff, trap more heat, and lower evapotranspiration. At the same time, increased heatwaves and rainfall due to climate change are amplified in urban areas due to feedbacks between cities and meteorological processes. Land surface models, the part of atmospheric models tasked with modeling the earth’s surface and hydrology, lack the fine-scale, ecohydrologic process representation in cities to capture important feedbacks between urbanization, hydrology, and near surface energy partitioning. For example, tree cover that shades pavement and enhances evapotranspiration is ubiquitous amongst many cities worldwide, but contemporary land surface models cannot allow for tree canopy to extend over pavements. Further, lateral transfers of surface water from impervious to permeable surfaces are critical for runoff reduction, like routing of rainfall to natural vegetation, but are similarly not represented. Lack of ecohydrologic processes is problematic because we are unable to predict the impact of increasingly common greening initiatives that feature both nature-based solutions, like increased tree cover, and green infrastructure practices, like permeable pavements and green roofs. These practices are targeted to reduce runoff and urban heat, but will likely modify other urban atmospheric processes like rainfall in unknown ways. Unfortunately, potential connections between urban greening initiatives and resulting changes to the urban climate have not been explored rigorously at city scale. In this project, we use Noah-MP for Heterogenous Urban Environments (HUE), a new land surface model capable of resolving fine-scale ecohydrologic processes like urban tree cover shading pavements and routing of surface water to permeable surfaces with multiple landcover types per grid cell (e.g. a mosaicking scheme) in urban spaces. We use HUE to examine the impact of widespread climate adaptation policy in multi-year WRF regional climate simulations centered on the coastal city of Milwaukee, Wisconsin, USA at convective permitting scales. Different landcover configurations that represent cases of city-wide greening are interpreted from an ambitious real-world regional urban greening “master plan.” We show that more greening leads to a reduction of runoff throughout the warm season, although partitioning of runoff reduction between evapotranspiration and deep drainage varies year to year. We also examine how changes in sensible and latent heat fluxes affect near surface meteorology within the city, generally increasing humidity and decreasing air temperatures. These differences are especially apparent during days of strong lake-breeze coupling between Milwaukee and nearby Lake Michigan. We further show that urban greening leads changes in rainfall event totals, peak intensities, and seasonal averages. While only for a single city, our results highlight that widespread urban greening changes not only urban hydrology but also urban hydrometeorology. This highlights that the evaluation of urban greening initiatives worldwide is critical for climate change adaptation and mitigation.

Urban regions substantially modify both surface energy and hydrologic cycles. Despite the linkage between urban hydrology and energy cycles, modern coupled land-atmosphere models do not represent common urban hydrologic features like runoff routing from impervious to pervious surfaces or tree canopy that shades pavements. We compare three urban surface models in the Weather and Research Forecasting model across multiple hydrometeorological events in Milwaukee, Wisconsin: a widely used slab urban model (Noah-MP Bulk Parameterization; Typical), multiple land covers per grid cell (Noah-MP Mosaic; Mosaic), and a model which adds sub-grid water transfers between land cover types (Noah-MP HUE; HUE). Inclusion of urban hydrology and vegetation (HUE) increases albedo and emissivity, reducing available energy in our study region. Ambient soil moisture conditions cause divergent responses in HUE simulations: warming when soil water is limited and cooling when ample soil water is available for evapotranspiration. Comparison against observed 2m air temperature and specific humidity show increased skill in the HUE model simulations, especially compared to the Typical model. Noah-MP HUE presents a stride in understanding how urban hydrology influences city-scale meteorology and a pathway to examine urban hydrologic greening initiatives more wholistically in regional atmospheric models.

Driven by the need for integrated management of groundwater (GW) and surface water (SW), quantification of GW–SW interactions and associated contaminant transport has become increasingly important. This is due to their substantial impact on water quantity and quality. In this review, we provide an overview of the methods developed over the past several decades to investigate GW–SW interactions. These methods include geophysical, hydrometric, and tracer techniques, as well as various modeling approaches. Different methods reveal valuable information on GW–SW interactions at different scales with their respective advantages and limitations. Interpreting data from these techniques can be challenging due to factors like scale effects, heterogeneous hydrogeological conditions, sediment variability, and complex spatiotemporal connections between GW and SW. To facilitate the selection of appropriate methods for specific sites, we discuss the strengths, weaknesses, and challenges of each technique, and we offer perspectives on knowledge gaps in the current science.

Although urbanization fundamentally alters water and energy cycles, contemporary land surface models (LSMs) often do not include key urban vegetation processes that serve to transfer water and energy laterally across heterogeneous urban land types. Urban water/energy transfers occur when rainfall landing on rooftops, sidewalks, and driveways is redirected to lawns or pervious pavement and when transpiration occurs from branches overhanging impervious surfaces with the corresponding root water uptake takes place in nearby portions of yards. We introduce Noah-MP for Heterogenous Urban Environments (Noah-MP HUE), which adds sub-grid water transfers to the widely used Noah-MP LSM. We examine how sub-grid water transfers change surface water and energy balances by systematically increasing the amount of simulated water transfer for four scenarios: tree canopy expanding over pavement (Urban Tree Expansion), tree canopy shifting over pavement (Urban Tree Shift), and directing impermeable runoff onto surrounding vegetation (Downspout Disconnection) or into an engineered pavement (Permeable Pavement). Even small percentages of sub-grid water transfer can reduce runoff and enhance evapotranspiration and deep drainage. Event-scale runoff reduction depends on storm depth, rainfall intensity, and antecedent soil moisture. Sub-grid water transfers also tend to enhance (reduce) latent (sensible) heat. Results highlight the importance not only of fine-scale heterogeneity on larger scale surface processes, but also the importance of urban management practices that enhance lateral water transfers and water storage-so-called green infrastructure-as they change land surface fluxes and, potentially, atmospheric processes. This work opens a pathway to directly integrate those practices in regional climate simulations. We develop an urban land surface model representation of impervious to pervious runon and canopy overhanging impervious surfaces Using idealized land use, we systematically examine the effects of lateral transfers on water and energy budgets over warm seasons We found large changes in runoff generation, water balances, and energy partitioning when lateral transfers are simulated

Tree rings can reveal long-term environmental dynamics and drivers of tree growth. However, individual ecological drivers of tree growth need to be disentangled from the effects of other co-occurring environmental and climatic conditions in tree rings to examine the histories of stand- to landscape-level ecological processes. Here, we integrate ecohydrological theory of groundwater–tree interactions with dendrochronological approaches and develop a new framework to isolate water-level effects on tree rings from climate induced variability in tree ring growth. Our results indicate that changing depth to groundwater within 1–2.3 m of the land surface exerts a substantial influence on red pine growth and this influence can be quantified and used to reconstruct long-term groundwater and lake level histories from tree ring patterns in Northern Wisconsin. This research suggests a substantial influence of groundwater on tree growth with implications for improving the mechanistic understanding of climate-induced tree mortality and reduce uncertainty in forest productivity models. Further, this is a transferable approach to isolate and reconstruct strong environmental drivers of tree growth that co-occur with other environmental signals.

Food-energy-water (FEW) systems are increasingly vulnerable to shocks. Repeated floods, worsening droughts, sudden tariffs, and disease outbreaks all underscore the importance of strengthening production systems during a time of rapid global change. However, the laws, regulations, and incentive programs that govern these sectors were often developed in isolation, creating fragmented and lagged responses to previous crises, ineffective governance of FEW security, and unintended effects even when achieving policy goals. Here, we examine the Mississippi River Basin in the Midwest US to illustrate how policies designed to address one challenge had other unanticipated consequences. We argue for a long view of the future that honors the interconnectedness of FEW sectors with ecosystems (FEWE); values non-provisioning ecosystem services; and prioritizes incentives that improve FEW production, farm profitability, and ecosystem health. Now is the time for reassessment of how well FEWE provide security to all humans and the environment, and to support integrated policies that avoid unintended future consequences.

We develop an urban land surface model representation of impervious to pervious runon and canopy overhanging impervious surfaces • Using idealized land use distributions, we systematically examine the effects of lateral transfers on water and energy over warm seasons • We found large differences in runoff generation, water balances, and energy partitioning between standard and lateral transfer simulations

In areas with seasonal snowfall, the spring snowmelt often accounts for a large percentage of annual groundwater recharge. As climates warm, midwinter snowmelts are becoming more common. Although midwinter melt events can cause discrete recharge events, they can also increase soil water content and leave the ground exposed to subsequent cold periods. Without the insulating effects of snow, frozen ground can develop, which can prevent infiltration during subsequent melt events, reducing recharge, and increasing overland flow. We investigated relationships between winter precipitation, the soil thermal regime, and recharge to determine the factors that contribute to variation in winter‐spring recharge. We found that statistically significant predictors of variation in winter‐spring recharge, controlling for precipitation, were amount and cover of snow, evapotranspiration/sublimation, air temperature, and number of freezeback events occurring between two melt events. We observed that midwinter snowmelt followed by freezeback and subsequent melt events correlated with lower than expected recharge. We quantify the occurrence of this sequence of events (snowmelt followed by freezeback and another melt) and demonstrate its effect in reducing recharge in a multiyear, multilocation statistical analysis. This finding indicates that frozen ground plays a role the partitioning of precipitation between recharge and runoff, but the effect is sensitive to the magnitude and temporal sequence of precipitation events and temperature fluctuations. Understanding the complex relationships between snow, midwinter melt and freezeback events, frozen ground, and recharge is critical for predicting how climate change will affect groundwater resources in the future.

Trees in the urban right-of-way areas have increasingly been considered part of a suite of green infrastructure practices used to manage stormwater runoff. A paired-catchment experimental design (with street tree removal as the treatment) was used to assess how street trees affect major hydrologic fluxes in a typical residential stormwater collection and conveyance network. The treatment consisted of removing 29 green ash (Fraxinus pennsylvanica) and two Norway maple (Acer platanoides) street trees from a medium-density residential area. Tree removal resulted in an estimated 198 m3 increase in surface runoff volume compared to the control catchment over the course of the study. This increase accounted for 4% of the total measured runoff after trees were removed. Despite significant changes to runoff volume (p ≤ 0.10), peak discharge was generally not affected by tree removal. On a per-tree basis, 66 L of rainfall per m2 of canopy was lost that would have otherwise been intercepted and stored. Runoff volume reduction benefit was estimated at 6376 L per tree. These values experimentally document per-capita retention services rendered by trees over a growing season with 42 storm events. These values are within the range reported by previous studies, which largely relied on simulation. This study provides catchment scale evidence that reducing stormwater runoff is one of many ecosystem services provided by street trees. This study quantifies these services, based on site conditions and a mix of deciduous species, and serves to improve our ability to account for this important yet otherwise poorly constrained hydrologic service. Engineers, city planners, urban foresters, and others involved with the management of urban stormwater can use this information to better understand tradeoffs involved in using green infrastructure to reduce urban runoff burden.

Fens are high conservation value ecosystems that depend on consistent discharge of groundwater that saturates the near surface for most of the growing season. Reduced groundwater inputs can result in losses of native diversity, decreases in rare-species abundance and increased invasion by non-native species. As such, fen ecosystems are known to be particularly susceptible to changes in groundwater conditions including reduction in water levels due to nearby groundwater pumping. However, research is lacking on whether floristic degradation is influenced by feedbacks between hydrology and soil properties. We present a model of an archetype hillslope fen that couples a hydrological niche model with a variably saturated groundwater flow model to predict changes in vegetation composition in response to different groundwater drawdown scenarios. The model explores a potential edaphic feedback through the use of an observed relationship between fen floristic quality and soil/peat water retention characteristics that is attenuated with separate edaphic and floristic memory terms representing lags in biophysical responses to dewatering. Model parameters were determined based on data collected from six fens in Wisconsin under various states of degradation. We observed different water retention characteristics between sites that were minimally impacted versus degraded that are likely due to peat decomposition, oxidation and compaction at the degraded sites. These characteristics were also correlated with floristic quality. The results reveal a complex response to drawdown where changes in peat hydraulic properties following dewatering lead to even drier conditions and further shifts away from typical fen species.

Calcareous fens are a rare type of groundwater dependent wetland with plant communities adapted to environmental stressors that include low nutrient availability, low oxygen availability, and various chemical toxicities. The conservation status/integrity of these plant communities is often quantified through floristic quality metrics that depend on intensive floristic inventories. Here we examine relationships between floristic quality, foliar chemistry, hydrology, and soil chemistry descriptors of six calcareous fens in southern Wisconsin in various states of degradation. Through examination of site descriptor correlations, Partial Least Squares Regression (PLSR), variation partitioning, and predictor variable stability analysis, we found foliar nutrient levels (e.g., foliar nitrogen and phosphorus) to be the strongest and most consistent predictors of floristic quality in these fens. Relationships between foliar nutrient levels, hydrology, and soil chemistry suggest water saturation is strongly linked to foliar nitrogen, phosphorus, and manganese. Since foliar nutrients are readily measurable both remotely and in-situ, our finding that foliar nutrients are strong predictors of floristic quality could have implications regarding monitoring the ecological integrity of these imperiled ecosystems.

First posted September 21, 2022 For additional information, contact: Director, Upper Midwest Water Science CenterU.S. Geological Survey1 Gifford Pinchot DriveMadison, WI 53726Contact Pubs Warehouse Urban forests have largely been overlooked for the role they play in reducing stormwater runoff volume by using hydrologic processes such as interception (rainfall intercepted by tree canopy), evapotranspiration (the transfer of water from vegetation into the atmosphere) and infiltration (percolation of rainwater into the Earth’s soil). Early research into the effects of trees on urban stormwater runoff used simple estimates based on assumptions of canopy coverage and design storm criteria. In a review of available literature on how capable urban trees are at reducing runoff, the Center for Watershed Protection (2017) found only six studies; three of them used measured data from a single plot, and the other three used models. When identifying gaps in research on the role of trees in stormwater management, Kuehler and others (2017) highlighted the need for studies that scale the local effects of urban trees to the larger sewershed catchment area, allowing a more holistic understanding of the urban tree canopy effects on hydrology.For these reasons, the U.S. Geological Survey, in cooperation with the U.S. Environmental Protection Agency, U.S. Forest Service, and the University of Wisconsin, quantified the effect of removing urban street trees and their canopy on stormwater generation in a medium-density residential area. Using a paired-catchment experimental design, rainfall-runoff relations were characterized in two medium-density residential catchments in Fond du Lac, Wisconsin, during May through September in 2018–20. Results of the study are detailed in Selbig and others (2022).During the calibration phase, hydrograph metrics from paired runoff events were used to develop the relation between the control and test catchments with street trees in place. The ability to measure changes to the rainfall-runoff response after removal of tree canopy was made possible by an aggressive tree removal program by the city as a response to rapid infestation from the Agrilus planipennis (emerald ash borer). In March 2020, a total of 31 street trees were removed at the onset of the treatment period, resulting in a loss of 2,990 square meters of canopy over streets, driveways, sidewalks, and grassed areas.

The CUAHSI Virtual University is an interinstitutional graduate training framework that was developed to increase access to specialized hydrology courses for graduate students from participating US institutions. The program was designed to capitalize on the benefits of collaborative teaching, allowing students to differentiate their learning and access subject matter experts at multiple institutions, while enrolled in a single course at their home institution, through a framework of reciprocity. Although the CUAHSI Virtual University was developed prior to the COVID-19 pandemic, the resilience of its online education model to such disruptions to classroom teaching increases the urgency of understanding how effective such an approach is at achieving its goals and what challenges multi-institutional graduate training faces for sustainability and expansion within the water sciences or in other disciplines. To gain faculty perspectives on the program, we surveyed (1) water science graduate program faculty who had served as instructors in the program, (2) water science graduate program faculty who were aware of the program, but had not participated, and (3) departmental chairs of participating instructors. Our data show widespread agreement across respondent types that the program is positive for students, diversifying their educational opportunities and increasing access to subject matter experts. Concerns and factors limiting faculty involvement revolved around faculty workload and administrative barriers, including low enrollment at individual institutions. If these barriers can be surmounted, the CUAHSI Virtual University has the potential for wider participation within hydrology and adoption in other STEM disciplines.

Urban forests are recognized as a nature-based solution for stormwater management. This study assessed the underlying processes and extent of runoff reduction due to street trees with a paired-catchment experiment conducted in two sewersheds of Fond du Lac, Wisconsin. Computer models are flexible, fast, and low-cost options to generalize and assess the hydrologic processes determined in field studies. A state-of-the-art, public-domain model, which explicitly simulates urban tree hydrology, i-Tree Hydro, was used to simulate the paired-catchment experiment, and results from field observations and simulation predictions were compared to assess model validity and suitability as per conditions in the broader Great Lakes basin. Model parameters were aligned with observed conditions using automatic and manual calibration. Model performance metrics were used to quantify the weekly performance of calibration and to validate predictions. Those calibration metrics differed substantially between the two periods simulated, but most calibration metrics remained positive, indicating the model was not fitting only the period used for calibration. Predicted avoided runoff for a five-month leaf-on period was 64 L/m2 of canopy, 4 % lower than the field-estimated avoided runoff of 66 L/m2 of canopy. Interception was the most directly comparable process between the model and field observations. Based on 5 storms sampled, field estimation of precipitation intercepted and retained on trees averaged 63 % and ranged from 22 % to 81 %, while model estimation averaged 61 % and ranged from 36 % to 99 %. This model was able to fit predictions to observed catchment discharge but required extensive manual calibration to do so. The i-Tree Hydro model predicted avoided runoff comparable with the field study and earlier assessments. Additional field studies in similar settings are needed to confirm findings and improve transferability to other tree species and environmental settings.

As we reckon with the effect of COVID-19 on the research enterprise in hydrologic science, it is important to acknowledge that disruptions will be persistent and that institutional-level adjustments, while helpful, are not sufficient to mitigate all impacts on hydrologic scientists. Here, we describe the breadth of research contributions in the hydrologic sciences, consider how the pandemic has impacted this portfolio of contributions, document one impact that is already being realized in publication of research, and suggest guidance to the hydrologic science community, institutions, review panels, and funding organizations in considering these impacts at various stages of hiring and promotion in our community. Acknowledging the diversity of contributions to research is particularly valuable because it provides a more objective, transparent, and holistic basis for evaluating individuals within the context of norms of the hydrologic science community. With clearly established values, it is easier to identify impacts of life events, such as those related to the COVID-19 pandemic, as they are manifested in individuals under a diversity of circumstances.

Understanding the role of trees in attenuating the timing and magnitude of effective precipitation reaching the land surface requires improved monitoring of interception dynamics. We developed a new field monitoring approach to leverage continuous monitoring of tree sway motion in quantifying continuous, dynamic time series of canopy water storage during storms. Using this approach, we additionally observed a hysteretic interception response in tree canopies, which indicates that interpreting interception processes through tree sway signals requires the consideration of changing water (i.e., mass) distribution during and following storms. These findings suggest that continuously monitoring tree sway motions offers a new technique to quantify interception processes. This advancement in whole tree interception may help improve our understanding of how interception affects ecosystem water availability/productivity and runoff dynamics that are important for both natural ecosystems and stormwater management in cities.