This paper discusses the most important policies and regulations supporting the decentralized management, harvesting and utilization of rainwater in Germany, where such measures have been increasingly applied during the last few decades. The development and implementation of specific policies and regulations contributed significantly to that trend. They also work as incentives for the development of advanced technologies and businesses as well as the widespread and growing implementation of measures for decentralized rainwater management, harvesting and utilization by public and private actors. This development can generally be associated with environmental and economic concerns related with required adaptation to changes in climate, demographic structures and infrastructures as well as climate resilience including flood control and drought resistance. The addressed and supported measures can be assigned to the two focus areas ‘Decentralized rainwater harvesting and utilization’, aiming for saving of precious fresh water resources and centrally supplied drinking water, as well as ‘decentralized rainwater retention and management’, aiming for flood control and protection of existing infrastructures and ecosystems. The decentralized management of rainwater and its separation from combined sewer systems at the source is generally regarded as the state of the art and basic condition for sustainable municipal wastewater management.

Households consume a significant fraction of total potable water production. Strategies to improve the efficiency of water use tend to emphasize technological interventions to reduce or shift water demand. Behavioral water use reduction strategies can also play an important role, but a flexible framework for exploring the “what-ifs” has not been available. This paper introduces such a framework, presenting an agent-based model of household water-consuming behavior. The model simulates hourly water-using activities of household members within a rich technological and behavioral context, calibrated with appropriate data. Illustrative experiments compare the resulting water usage of U.S. and Dutch households and their associated water-using technologies, different household types (singles, families with children, and retired couples), different water metering regimes, and educational campaigns. All else equal, Dutch and metered households use less water. Retired households use more water because they are more often at home. Water-saving educational campaigns are effective for the part of the population that is receptive. Important interactions among these factors, both technological and behavioral, highlight the value of this framework for integrated analysis of the human-technology-water system.

This paper examines the planning paradigm shift related to the contested “urban renaissance” mega-project in Downtown Seoul (Korea). Similar to other global cities, over the last few decades, different mega-projects have been successfully implemented in Seoul. These projects have been considered engines for urban renewals and transformation. This paper builds on the analysis of the failure and re-framing planning strategy for the Green Corridor (GC) mega-project, part of the “Urban Renaissance Master Plan for Downtown Seoul”. The GC case reveals various critical insights for urban sustainability: (i) the current mega-projects’ sustainability fallacy, related to top-down, technocratic densification, and greening practices; and (ii) the untapped potential of Asian traditional and irregular small scale urban patterns, and their related socio-cultural value in addressing the renaissance of the long term urban sustainability. In particular, the discussed research findings point out that urban renaissance enabling sustainability principles requires integrated, small scale, incremental, and adaptive (stepwise) urban planning and design processes that go well beyond general strategies following the so-called “green growth” paradigm.

Urbanized delta areas worldwide share a growing tendency of exposure to water stress induced by the effects of climate change and anthropogenic factors, threatening the operation of infrastructure systems and future urban development. The important synergistic impacts coexisting with freshwater scarcity are increasing urbanization rates, subsiding soils, saltwater intrusion in aquifers and rivers, coastal erosion, and increased flooding. Innovative design strategies and concepts for the integration of decentralized rainwater management measures can contribute to the integrated and climate resilient planning of urban spaces that are threatened by climate change scenarios that worsen the security of urban infrastructures and the future availability of fresh water. Decentralized rainwater management, including retention, storage, and reuse strategies that are integrated into spatial planning and urban design, can reduce flood risks while simultaneously enhancing freshwater availability. This paper discusses a paradigm shift in urban water management, from centralized to decentralized management (that is, from threats to opportunities), using the example of two case studies. Concepts and strategies for building climate resilient cities, which address flood control, the protection of freshwater resources, and the harmonization of a natural and more sustainable water balance, are presented for Almere (Rhine Schelde Delta, The Netherlands) and Hsingchu (Dotzpu Delta, Taiwan).