The changes of streamflow quality and quantity under urban development impact

Abstract

Urban development presents both challenges and opportunities for urban hydrology. For instance, human-driven stressors like climate change and urbanization have been found to impact the various components of the hydrological cycle. Pollution caused by population growth and economic development can result in poor water quality in river flows. Urbanization processes such as deforestation, wastewater discharge, and urban stormwater runoff can also lead to point and nonpoint source pollution, affecting the entire watersheds. However, there are anthropic control measures, such as blue-green infrastructure (BGIs), which aim to restore water quantity and quality, and are being implemented at both local and catchment scales. While the effects of BGIs on water quantity and quality restoration vary among catchments and climate zones, they offer a promising solution to address the challenges posed by urbanization. This study aims to investigate the impacts of urban development on urban hydrology, particularly streamflow quantity and quality. The study will explore the main stressors and measures involved in urbanization, construction works, river self-purification, blue-green infrastructure (BGIs), and climate change. In a subtropical climate, we propose a novel approach to correlate water quality with urbanization signatures and construction works. Our findings reveal that nutrients and pathogens exhibit consistently decreasing long-term trends in Hong Kong. The impacts of urbanization on station nutrients and pathogens are unevenly distributed. Construction works impact stream water quality through dissolved and suspended solids, with key construction work signatures increasing water temperature and pH. Dissolved oxygen concentrations are influenced by construction works and rainfall. In terms of river self-purification, wet seasons exhibit stronger self-purification capabilities compared to dry seasons in Hong Kong. High-flow months show dominant self-purification capacities in reducing pollutants. Flow rate is predicted to promote acidification, water degradation, and solid pollution. Wet seasons improve water quality by reducing BOD5, NH3-N, and tolerating high DO levels. Additionally, the implementation of BGIs in future urban development has been shown to have the most significant increase in peak flow and total runoff volume compared to the current urban development phase, which primarily involves construction works, during peak and total amount increase-oriented rainfalls. This study examines the hydrological responses of an urban catchment to climate change and urbanization in cold climates. The impacts of climate change on total and peak runoff during extreme precipitation events are investigated. Additionally, urban streamflow is shown to be clearly influenced all year-round under both Representative Concentration Pathways 4.5 and 8.5 (RCP4.5 and RCP8.5, respectively). Snowpack and snowmelt, which are crucial components of the high-latitude hydrological cycle, are also found to be impacted by climate change. The study also compares and identifies the differences and relationships between the impacts of climate change and urbanization. Results indicate that climate change will have a more significant impact on the seasonal distribution of urban streamflow, while urbanization, reflected by changes in imperviousness, has a direct impact on streamflow. Overall, the research aims to expand our understanding of the main impacts of urban development on urban hydrology at catchment scales under different climate zones.