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Nonpoint source (NPS) pollution is a pressing issue worldwide, especially in the Chesapeake Bay, where sediment, nitrogen (N), and phosphorus (P) are the most critical water quality concerns. Despite significant efforts by federal, state, and local governments, the improvement in water quality has been limited. Investigating the spatial distribution of NPS hotspots can help understand NPS pollutant output and guide control measures. We hypothesize that as land cover changes from natural (e.g., forestland) and agricultural to suburban and ultra-urban, the distribution of NPS pollution source areas becomes increasingly spatially uniform. To test this hypothesis, we analyzed three real watersheds with varying land cover (Greensboro watershed for agriculture, Watts Branch watershed for suburban, and Watershed 263 for ultra-urban) and three synthetic watersheds developed based on the Watts Branch watershed, which ranged from forested and agricultural to ultra-urban but had the same soil, slope, and weather conditions. The Soil and Water Assessment Tool (SWAT) was selected as a phenomenological model for the analysis, and SWAT-CUP was used for model calibration and validation. The hydrologic responses of the three real and synthetic watersheds were simulated over ten years (1993–2002 or 2002–2011), and calibration and validation results indicated that SWAT could properly predict the export of runoff and three target NPS pollution constituents (sediment, total nitrogen, and total phosphorus). The results showed that the distribution of NPS pollutant outputs becomes increasingly uniform as land cover changes from agriculture to ultra-urban across watersheds. This research suggests that the spatial distribution of NPS pollution source areas is a function of the major land cover category of study watersheds, and control strategies should be adapted accordingly. If NPS pollution is distributed unevenly across a watershed, hotspot areas output a disproportionate amount of pollution and require more targeted and intensive control measures. Conversely, if the distribution of NPS pollution is more uniform across a watershed, the control strategies need to be more widespread and encompass a larger area.more » « less
We develop the first spatially integrated economic-hydrological model of the western Lake Erie basin explicitly linking economic models of farmers' field-level Best Management Practice (BMP) adoption choices with the Soil and Water Assessment Tool (SWAT) model to evaluate nutrient management policy cost-effectiveness. We quantify tradeoffs among phosphorus reduction policies and find that a hybrid policy coupling a fertilizer tax with cost-share payments for subsurface placement is the most cost-effective, and when implemented with a 200% tax can achieve the stated policy goal of 40% reduction in nutrient loadings. We also find economic adoption models alone can overstate the potential for BMPs to reduce nutrient loadings by ignoring biophysical complexities. Key Words: Integrated assessment model; agricultural land watershed model; water quality; cost-share; conservation practice; nutrient management JEL Codes: H23, Q51, Q52, Q53more » « less
This study examined simulated changes in total (and outdoor) water demand with increased dwelling units per unit area (DUUA) for seven building types (BTs) in the Denver Water service area. We utilized the Denver Water Demand Model — a spreadsheet tool that uses inputs such as BT, population, household size, number of units, etc. — to develop an “agent‐based” simulator to permit scenario analyses of future water use for different mixes of BTs. We examined household “movement” for new residents from lower density to higher density classifications. Increased residential density can be achieved through multiple pathways. For instance, a family could move from a large single‐family (LSF) unit to a single‐family home with a smaller lot footprint (SSF). Or, a family could move into a multi‐family housing development from a SSF. Our results suggest uneven, nonlinear efficiency gains in water use with increased density, depending on the specific BT movements. Simulation outputs indicate that the greatest gains in water savings per unit change in DUUA can be achieved with short movements over the lowest density classes (e.g., LSF to a SSF). In addition, results suggest that increasing irrigation efficiency (less water applied per unit area irrigated) may decrease total residential water demand by 5% to 25% over baseline; efficiency of irrigation may prove to be as effective, if not more, at reducing residential water demand as increasing housing density.
Urban development is occurring in many Sub-Saharan Africa cities and rapid urbanization is underway in the East African city of Addis Ababa, Ethiopia. In an effort to address urban poverty and increase homeownership opportunities for low and middle-income residents, the City Administration of Addis Ababa initiated a large-scale housing development project in 2005. The project has resulted in the completion of 175,000 units within the city with 132,000 more under construction. To understand the impacts of both rapid growth and the housing program’s impact on the city’s urban form, we compared the type and distribution of land uses in Addis Ababa, Ethiopia, between 2006 with 2016 using hand-digitized, ortho-rectified satellite images in Geographic Information Systems (GISs). While residential density has increased, overall density has decreased from 109 people/ha to 98 people/ha. We found that between 2006 and 2016, land occupied by residential housing increased from 33% to 39% and the proportion of informal housing decreased from 57% to 38%. Reflecting the country’s economic prosperity, there was a dramatic increase in the presence of single family housing, particularly on the city’s western side. In 2006, only 1% of residential areas were occupied by high-rise condominiums (4 floors or greater) and this increased to 11% by 2016. The majority of the new, higher density residential developments are located near the eastern edges of the city and this outlying location has significant implications for residents, infrastructure construction, and future development.more » « less
Although extreme heat can impact the health of anyone, certain groups are disproportionately affected. In urban settings, cooling centers are intended to reduce heat exposure by providing air-conditioned spaces to the public. We examined the characteristics of populations living near cooling centers and how well they serve areas with high social vulnerability.
We identified 1402 cooling centers in 81 US cities from publicly available sources and analyzed markers of urban heat and social vulnerability in relation to their locations. Within each city, we developed cooling center access areas, defined as the geographic area within a 0.5-mile walk from a center, and compared sociodemographic characteristics of populations living within versus outside the access areas. We analyzed results by city and geographic region to evaluate climate-relevant regional differences.
Access to cooling centers differed among cities, ranging from 0.01% (Atlanta, Georgia) to 63.2% (Washington, DC) of the population living within an access area. On average, cooling centers were in areas that had higher levels of social vulnerability, as measured by the number of people living in urban heat islands, annual household income below poverty, racial and ethnic minority status, low educational attainment, and high unemployment rate. However, access areas were less inclusive of adult populations aged ≥65 years than among populations aged <65 years.
Given the large percentage of individuals without access to cooling centers and the anticipated increase in frequency and severity of extreme heat events, the current distribution of centers in the urban areas that we examined may be insufficient to protect individuals from the adverse health effects of extreme heat, particularly in the absence of additional measures to reduce risk.