Steven P. Loheide

Ecohydrologic processes influence urban water and energy cycles including convective rainfall. Coupled land‐atmosphere models, however, lack fine‐scale representation of urban ecohydrology processes. This study integrates these processes into ensemble land‐atmosphere simulations to assess changes in convective rainfall in Milwaukee, Wisconsin. We compare simulations using existing urban land surface representations to ones that resolve processes like tree canopy overhanging pavement and runoff routing from impervious to pervious surfaces. We find that ecohydrologic processes produce cooler and wetter conditions ahead of rainfall due to higher evapotranspiration, especially under weak atmospheric forcing. Simulated rainfall aligns more closely with observed rainfall when ecohydrologic processes are considered, especially in an area of known urban rainfall intensification; more of this rainfall infiltrates. Our findings highlight the importance of model representation of urban ecohydrology to better understand rainfall holistically and the importance of representing these processes for precipitation forecasts and for exploring future city‐scale climate adaptation strategies.

Agrivoltaic performance and ecosystem impacts are understudied in humid temperate climates, especially across photovoltaic (PV) configurations. We established an agrivoltaic observatory in Wisconsin, USA, comparing an open-sky control with fixed-tilt and single-axis tracking arrays. Continuous radiation, eddy-covariance, soil moisture/temperature, and phenocam observations were paired with vegetation surveys across below-panel, dripline, and alley microhabitats. Clear-sky radiation showed that fixed-tilt panels created persistent below-panel and shaded-side diffuse-dominated light conditions, whereas tracking arrays redistributed shade through the day and increased under-row light. Across May–November 2025, soils in the fixed-tilt were driest at intermediate-to-deep depths, while the tracking maintained the highest deep soil moisture. Within the fixed-tilt, below-panel soils were coolest, yet also among the driest, indicating that throughfall exclusion outweighed reduced evaporative demand as a control on moisture dynamics. Driplines accumulated water at intermediate depths, consistent with rainfall and infiltration concentration along panel edges. Tracking reduced within-array heterogeneity and maintained deeper water storage by uniformly suppressing evapotranspiration through shifting shade. The array showed lower net CO2 uptake and evapotranspiration than control during June–October by 43% and 33%, respectively, alongside higher sensible heat fluxes and lower relative humidity. Flux differences increased after early-August mowing and herbicide application, suggesting vegetation management can rival microclimate in shaping first-year outcomes. Overall, humid climate agrivoltaic systems form repeatable microhabitat mosaics rather than uniformly cooler or wetter conditions, with array geometry governing light limitation, rainfall redistribution, and vegetative impacts. Our dataset provides a baseline for multi-year evaluation of carbon, water, and productivity tradeoffs.

Coastal forests of the North American Great Lakes have long provided ecological, economic, and cultural resources. However, extensive logging and shoreline development have greatly reduced the number of well-preserved coastal forests, leaving ridge-and-swale complexes among the most intact examples remaining in the region. These freshwater coastal landscapes formed from ancient beaches, creating sandy, tree-covered ridges separated by low-lying interdunal swales that commonly support wetlands. Ridge-and-swale complexes serve as the transition between upland ecosystems and the Great Lakes along which interaction with groundwater directly controls vegetation composition and function. They are an excellent natural setting to study forest-groundwater interactions as variation in groundwater depth impacts water available to plants. In these systems, groundwater hydrology reflects the combined influence of upland derived regional groundwater flow, local hydrologic inputs (precipitation) and outputs (evapotranspiration), and variability in Great Lakes Water Levels (GLWL). As environmental conditions and GLWLs continue to shift the trajectory of these tightly coupled groundwater-ecosystems interaction remains uncertain.The goal of this work is to document modern spatial and temporal variation in forest-groundwater interactions, establish the influence of depth to groundwater on historical tree growth, and map forest susceptibility to groundwater conditions in a ridge-and-swale complex at the Ridges Sanctuary in Bailey’s Harbor, WI (45.075163, -87.108379). To investigate modern forest water use and groundwater dynamics, we instrumented a ridge-and-swale complex situated along Lake Michigan with shallow groundwater wells. Over 18 months, analysis of daily fluctuations in groundwater revealed that evapotranspiration from groundwater differs in timing and magnitude between stands of trees. Throughout the ridge-and-swale complex groundwater levels respond differently throughout the year and especially during extended dry periods. This indicates a limit of tree water use based on depth to groundwater and differing influence of regional groundwater and GLWL sources. To investigate historical tree growth, we evaluated tree-ring metrics (basal area increment (BAI), ring widths, earlywood, and latewood) from Pinus strobes and Pinus resinosa to quantify tree growth variability across the ridge-and-swale complex. Chronologies for 120 trees were established with a majority spanning over 125 years from throughout the ridge-and-swale complex with limited trees documenting growth starting in the late 1700s. Comparison of BAI and relative elevation have revealed both tree species experience differing levels of anoxia and water stress based on position in the landscape and depth to groundwater, indicating that annual variability in groundwater is recorded in tree growth. To map future susceptibility to groundwater conditions, we used our established chronologies to decipher where trees showed resilience to the influence of GLWLs. Preliminary analyses suggest that stands situated in areas supported by regional groundwater flow have historically experienced optimal tree growth throughout the period of record. Conversely, the influence of GLWL supporting or hindering tree growth depends on position relative to the coast and the stage of Lake Michigan at the time. These findings not only shed light upon the previously unknown historical influence of GLWL on coastal ridge-and-swale ecosystems but help shape future management for coastal aquifers and forests.

Ecohydrologic processes change urban water and energy cycles, influencing convective rainfall. Coupled land-atmosphere models, however, lack the ability to represent urban ecohydrology. This study integrates fine-scale urban ecohydrologic processes into land-atmosphere simulations to assess changes in convective rainfall during ten events in Milwaukee, Wisconsin. We compare simulations that resolve processes like tree canopy overhanging pavement and runoff routing from impervious to pervious surfaces to existing urban land surface representations. We find that detailed representation of urban ecohydrology produces cooler and wetter atmospheric conditions ahead of rainfall due to higher evapotranspiration. Further, more rainfall is infiltrated during storms. Simulated rainfall aligns more closely with observed rainfall when ecohydrologic processes are considered, especially in an area of known urban rainfall intensification. Our findings highlight the importance of proper model representation of urban ecohydrology to better understand rainfall mechanisms and to improve the flexibility of models for exploring city-scale climate adaptation strategies.

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.

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.

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.

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.

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.