Effects of Land Cover Change on Water Quality in Urban Streams at Two Spatial Scales

This study examines the relationships between land cover change and water quality change in three urbanizing watersheds in the Pacific Northwest region of the United States: Burnt Bridge Creek, Salmon Creek, and the Tualatin River. All three watersheds have had many of their water quality parameters exceeding Total Maximum Daily Loads as required by their state’s environmental agencies in the past decades. By using the National Land Cover Datasets classified by the United States Geological Survey (USGS) for 1992, 2001 and 2006 and water quality data for a period between 1991 and 2010, this paper aims to examine whether changes in land cover are causing changes in water quality at two different spatial scales - at the sub-watershed scale and at a 100 meter riparian buffer scale. We used spatial regression models to identity the major determinants of changes in water temperature (WT), total suspended solids (TSS), dissolved oxygen (DO), and total phosphorus (TP) over time at different scales. The results show that each parameter reacts differently to land cover change depending on the scale of analysis. Both DO and WT showed significant relationships with land cover parameters on the watershed scale but not as much on the riparian buffer scale. TP shows significant relationships at the watershed scale, but TSS shows no significant relationships at the watershed scale. WT shows the only significant change in water quality over the past twenty years and is positively related to change in urban land cover. Topographic variables become significant in explaining the variations in WT and TP at the riparian scale. DO is mostly explained by mean slope for both 1992 and 2001 at both scales, but urban land cover became an important predictor in 2006 at both scales. Our analysis also suggested that there may be a potential lag between changes in land management and changes in water quality across different scales

Effects of Stormwater Green Infrastructure on Watershed Outflow: Does Spatial Distribution Matter?

Green Stormwater Infrastructure (GSI) has become a popular method in urban stormwater management. We examined how spatial distribution of GSI affected rainfall-runoff relationships in a recently developed neighborhood in Gresham, Oregon, USA for the 2017-2018 water year. Runoff ratio, peak discharge, and flashiness were compared under four precipitation scenarios (of differing intensity and duration) and different spatial arrangements of GSI. Distributed GSI reduced runoff ratio (10 - 20%), peak discharge (26 - 68%), and flashiness index (56 - 70%). Distributed GSI outperformed centralized structures for all metrics, reducing runoff ratio (22 - 32%), peak discharge 67 to 69%, and flashiness index (32 - 62%). This research serves as a basis for urban stormwater managers to understand potential impact of GSI on reducing runoff and downstream flooding in small urban watersheds with frequent rain

Spatial Analysis of Streamflow Trends in Burned Watersheds across the western contiguous United States

Despite increasing magnitude and frequency of wildfire, understanding hydrological processes contributing to changes in streamflow is not well examined for the entire western contiguous United States (WCONUS). This study provides insight into whether considering spatially varying watershed characteristics, including burn severity patterns, can better explain streamflow trends at broad spatial and temporal scales. Standard geographically weighted regression (GWR) and multi-scalar (MS) GWR were benchmarked against ordinary least squares (OLS) regression to determine if spatially varying coefficients could better explain spatially varying patterns and processes of peak flow, low flow, center timing of flow, and flashiness trends in burned watersheds. In most cases, GWR reduced spatial autocorrelation and provided insight into regional factors explaining streamflow trends. Both OLS and GWR models did not find burn severity-based metrics significant in explaining streamflow trends, except the peak flow trends model that included the spatial arrangement of high severity patches quantified using landscape shape index (LSI). Positive peak flow trends coincided with increasing LSI values in Northern California and negative peak flow trends with increasing LSI in the southern WCONUS. This research could guide regionally specific post-fire response and inform the development of new spatial metrics that could better represent post-fire hydrological processes

Event Scale Analysis of Streamflow Response to Wildfire in Oregon, 2020

Wildfire increases the magnitude of runoff in catchments, leading to the degradation of ecosystems, risk to infrastructure, and loss of life. The Labor Day Fires of 2020 provided an opportunity to compare multiple large and severe wildfires with the objective of determining potential changes to hydrologic processes in Oregon Cascades watersheds. Geographic information systems (GIS) were implemented to determine the total percentage burned and percentage of high burn severity class of six watersheds on the west slope of the Oregon Cascade Range. In addition, two control watersheds were included to contrast the influence of climatic effects. Spatial arrangements of burned patches were investigated for correlation to streamflow response by utilizing landscape metrics algorithms, including Largest Patch Index (LPI), mean gyration (GYRATE), Contiguity Index (CONTIG), Patch Cohesion Index (COHESION), and Clumpiness Index (CLUMPY). Results of the first-year post-fire response were consistent with other studies of fire effects in the Pacific Northwest (PNW) and indicated changes to runoff dynamics were difficult to detect with inferential statistics, but the largest changes in runoff coefficients occurred in watersheds having the greatest percentage burned. Correlation analysis indicated relationships between event runoff coefficients and percentage burned during the 2020 fire season. Control watersheds show confounding runoff coefficients, point to the influence of ongoing drought, and complicate conclusions about the role of spatial burn severity patterns. These results could guide future post-fire studies of spatial patterns of burn severity and could assist watershed managers to prioritize at-risk PNW catchments to minimize harm to ecological and societal values

A Geospatial Tool for Wetland Prioritization at the Watershed Scale

There is an increasing demand for assessing ecosystem functions for freshwater wetlands, especially when comparing or prioritizing among wetlands at the watershed scale. We estimated the relative potential of selected ecosystem functions for freshwater wetlands within a watershed using widely available geospatial data. We developed four functions to estimate 1) flood storage, 2) late season flow, 3) sediment retention and 4) temperature control in four pilot watersheds in Oregon (Tualatin, Coquille, Upper Grande Ronde and Sprague). These watersheds are geographically separated from each other representing diverse ecoregion environments. Spatial analysis and geographic information system (GIS) were designed for maximum re-use, based on publicly-available data, commonly-used software, semi-automated techniques and wetland characterizations that attempt to capture fundamental wetland processes. Our data sources include 30-meter digital elevation models, NRCS soil survey extracts, USGS National Land Cover Data, USGS HUC8 boundaries (polygons) and statewide wetland delineations (polygons) processed within ArcGIS 10.2 and Python 2.7.5 software. Model parameters were compiled using multiple proxy values for size, slope, aspect, proximity, flow path distance, hydrologic gradient, shade, and soil characteristics. WPT characterizations emphasize the multi-faceted value of freshwater wetlands, relating potential within a watershed as well as providing model-based characterizations between watersheds. Our wetland prioritization tool (WPT) provides useful information to estimate and compare the relative potential for selected wetland functions, thereby improving success in wetland conservation, restoration, and mitigation efforts

Urban sustainability Implementation and Indicators in the United States: A systematic review

Urban sustainability is the goal of many cities in the world, yet very few have achieved a level of sustainability that goes beyond the most basic environmental objectives. The practice and assessment of sustainability implementation are greatly compounded by lack of funding, technical know-how, political will, and the power disparity between dominant institutions and marginalized communities. This systematic analysis of urban sustainability literature involved the review of 241 studies published between 2010 and 2022. We critically examined current debates and challenges in urban sustainability, identifying gaps and opportunities and providing recommendations for creating equitable, just, and sustainable urban futures. We also reviewed 23 studies to summarize the social, ecological, and technological systems (SETS) indicators used to measure urban sustainability in the same period, many of which may not be relevant to the lived experiences of marginalized communities. To move toward more meaningful and equitable pathways, it is important to develop SETS indicators of urban sustainability that are reflective of the experiences and priorities of diverse groups in society. This review identifies four major issues in the current urban sustainability literature: space, scale, stakeholders, and dimension. These issues need to be centered in sustainability planning in order to develop solutions that are appropriate for the local context

Understanding Perspectives on Climate Hazards, Water Management, and Adaptive Transformation in an Exurban Community

Climate change and exurban development pose challenges for water resources. This paper examines the perceptions and adaptive responses to those stressors among stakeholders engaging in exurban water management. Drawing on 42 interviews with planners, water managers, and local experts, we analyze perspectives on water-related hazards in the Hood River watershed, Oregon, and identify contrasting approaches to adaptation. Interview subjects identified climate-related hazards as most significant, with relatively less – although not insignificant – concern about development. Interviewees understood the role of the Watershed Group in four different ways: resistance to change, sustaining the present system, adapting to improve resilience, or transformational adaptation. Despite tensions between these approaches, the Watershed Group empowers local actors, offering grounds for social development. This study indicates that exurban areas may be poised to experiment and develop methods of collaborative resource management that reconcile different interests toward transformational adaptations to the dual challenges of climate change and urbanization

Sensitivity of Urban Water Consumption to Weather and Climate Variability at Multiple Temporal Scales: The Case of Portland, Oregon

The sensitivity of municipal water consumption to climate and weather variability is investigated for Portland’s water provider service area between 1960 and 2013. The relationship between detrended seasonal urban water use (the difference between total water use and base use) and weather and climate variables (precipitation, maximum temperature) is examined at daily, monthly, and seasonal scales using stepwise multiple regression and autoregressive integrated moving average (ARIMA) models. At a seasonal and a monthly timescales, interannual variation in maximum temperature is the most important predictor of seasonal water consumption per capita, explaining up to 48% of the variation in seasonal monthly water consumption in June and July. At a daily scale, one-day lagged seasonal water demand and maximum temperature are the variables that are significant in all the daily models. Together with day of the week and precipitation, these variables explained up to 87 % of the variation in seasonal daily water consumption in summer. ARIMA models that take into account temporal autocorrelation explain between 70 and 81% of daily seasonal water consumption in summer months. This study provides useful climate information to urban water resource managers for seasonal water consumption forecasting at multiple temporal scales. Our results demonstrate the sensitivity of seasonal urban water consumption to climate variables as the scale of analysis changes. Urban water managers can use such information to establish proactive seasonal water resource management plans under increasing pressure from potential climate change, as understanding of the climatic sensitivity of seasonal water consumption is necessary for responding to changes

Virtual Water and Agricultural Exports During Recent Drought in California

In recent years, the western United States has been experiencing severe droughts. In this paper we focus on the state of California, which has a complex and vast water conveyance and irrigation system to support intensive agricultural production. We examine agricultural production and exports, in particular ‘virtual water’ exports, to better understand whether and how agricultural producers responded to recent drought conditions. We specifically focus on agricultural exports from 2010 to 2019 in order to better understand virtual water export during the recent drought. We show that despite occurrence of severe drought, California growers have largely continued their agricultural production and exports. The value of agricultural exports between 2010 and 2019 increased by 1.5 times. Water-intensive agricultural products, including dairy products and tree nuts, represent a high proportion of agricultural exports. This persistence of agricultural production and export is made possible due to a reliance on water management strategies that are unsustainable in the long term—primarily, in the case of California’s Central Valley, overdraft of groundwater. We argue that despite recent policy advances such as attempts to control groundwater overuse, California’s continued agricultural production and export system exacerbates an unsustainable situation, given persistence of drought conditions and the need to support many other human and ecological water uses