Chapter 1 delves into global urbanisation dynamics, honing in on urban water challenges, notably in the context of China’s accelerating urbanisation. Urbanisation, a transformative global force, triggers societal, economic and environmental shifts, offering opportunities for progress if managed adeptly. However, the chapter underscores the escalating water challenges accompanying this phenomenon. Urban floods, propelled by expanding impervious areas, pose substantial global threats, inducing economic losses. The intensified urbanisation aggravates water scarcity, fuelling conflicts and impacting ecosystems. Urban development contributes to water pollution, upsetting natural balances and escalating pollutant concentrations, resulting in ecological degradation. The urban heat island effect exacerbates these challenges, affecting ecosystems and local weather patterns. This chapter provides a nuanced exploration of the intricate relationship between urbanisation and water challenges, emphasising the urgent need for sustainable urban development practices.

Chapter 3 explores the impacts of urbanisation on the hydrological cycle, specifically the storm hydrograph. The replacement of vegetation with impermeable surfaces and the channelling of water in urban areas contribute to flooding and pollution events. The chapter emphasises the interdependence of flood risk management and water quality improvement in urban environments, stressing the importance of considering both aspects. Structural solutions for sustainable water quality improvements in urban stormwater such as Sustainable Drainage Systems (SuDS) are explored, covering flood resilience, benefits, sustainable drainage approaches, evidence of SuDS efficacy, their maintenance and integration into water-sensitive urban design (WSUD) for the entire city.

This chapter explores the potential of using sediment cores from floodplain lakes to assess contaminant levels in riverine flood deposits. It emphasises the limited knowledge about contaminants carried by floodwaters and their risks due to a lack of long-term monitoring data. Sediment cores offer a solution by preserving historical events, enabling the reconstruction of past contaminant levels. Theoretical background and methods for identifying historical flood deposits in sediment cores are discussed, along with temporal trends in waterway pollution. Case studies from Australia and Canada demonstrate the technique’s contribution to understanding the contamination levels in sediments deposited by river floods. Acknowledging the need for refinement, the chapter calls for a better understanding of uncertainties and the development of models to convert contaminant levels in flood deposits to those in the water column. Despite being in its early stages, the use of sediment cores holds great potential for enhancing flood risk assessment and management.

Floods, encompassing river, pluvial, and coastal types, are global disasters causing fatalities, infrastructure damage and ecosystem disruptions. This book fills a research gap by examining the underexplored facet of floods: their impact on water quality. Addressing the nexus of floods, climate change and water quality, it underscores escalating risks from heavy rainfall events, including pollutant mobilisation resulting to water pollution and coastal salinisation. Focussed on urbanisation, the book explores diverse flood types, offering insights into adaptive strategies such as sustainable urban design and sustainable urban drainage systems (SUDS). It emphasises integrating water quality considerations into flood risk management and introduces an online forecast model for urban flooding, highlighting the importance of early warning systems. Case studies and data from Canada, Australia, India, France and China illuminate real-world impacts. The book significantly advances understanding of floods’ multifaceted effects on water quality, providing practical approaches to mitigate challenges in this changing climate and identifying gaps of knowledge that need to be researched.

Chapter 5 explores the imperative need for early warning systems in predicting pluvial flood events in urban areas, focussing on hydraulic interactions and contaminant transport. Urban regions face increased vulnerability due to high population density and extended impervious surfaces. With pluvial floods occurring suddenly and posing a high risk to life and property, the chapter underscores the importance of real-time forecasting to minimise damages. It addresses the challenges in modelling water fluxes in cities, emphasising the complexity of physically based models and input requirements. The discussion extends to the coupling of urban flow and transport models, highlighting the need for efficient control strategies. The chapter also presents a case study in Oberricklingen, Hannover, Germany, showcasing the application of the developed models and concluding that an ANN-based model is optimal for spatially uniform rain events..

Chapter 4 explores the challenges posed by urbanisation on water quality, particularly during extreme rainfall events. The chapter traces the historical development of sewer systems designed to channel stormwater out of cities and into water bodies, emphasising the subsequent need for wastewater treatment to protect water sources. The proliferation of impervious surfaces in cities has led to increased flooding, prompting the construction of larger sewers, albeit quantity-focussed solutions. This approach, coupled with the misconception that stormwater is uncontaminated, exacerbates environmental pollution. The chapter advocates for comprehensive urban drainage management during floods to minimise water pollutants. Storm water tanks and SUDs are mentioned as means to reduce pollution loads to reach water bodies. It discusses the factors crucial for effective management, ranging from maintenance and short-term rain forecasting to the importance of pollutographs in long-term planning. Emphasising citizen involvement and a shift towards sustainable drainage techniques, the chapter provides insights for preserving urban environments amidst increasing extreme rainfall events and climate change threats.

Chapter 11 concludes a thorough analysis of urbanisation, the urban water cycle, and escalating urban floods. The chapter underscores the global changes and projects a substantial urban population increase by 2050. Emphasising the importance of the urban water cycle, it explores the impact of the COVID-19 pandemic on urban water demand. Addressing urban floods’ rising threat due to climate change, heat island effects and intense rainfall, the chapter advocates differentiated approaches and basin–city linkages for effective flood risk management. Prevention strategies, including early warning systems, SuDS and WSUD, are discussed, promoting a holistic understanding of urban water challenges. The chapter calls for increased research, data collection and interdisciplinary collaboration, highlighting UNESCO’s IHP role in promoting ecohydrology and sustainable urban water management, emphasising science-based solutions and policy development. This book somehow advanced the problems raised during the 2024 Olympics games when good water quality was expected to have in the Seine river for aquatic competitions. Not floods but extreme events episodes made it clear that rainfall conveys pollutions to water bodies from soil and neighbouring urban areas. Water runoff, the invisible sources of pollutants, is real and actions and research need to be undertake for its control, so far and with the current stage if knowledge only once pollution has been produced.