Liveable cities: Current environmental challenges and paths to urban sustainability

Population-environment dynamics across world's top 100 urban agglomerations: With implications for transitioning toward global urban sustainability

Urbanization is a long-term global trend critical for shaping human-Earth sustainability in the Anthropocene. In past decades, much progress has been made in researching urban sustainability, particularly global assessments of the big picture and case studies of individual cities. Here we examine the world's top 100 urban agglomerations (UAs) in terms of size-that rank high on sustainability agendas and cover 28% of the global UA area-regarding four broadly concerned challenges: population shrinkage, slum development, greenness loss, and heat exposure. Instead of merely focusing on global/regional "averages" or individual cases, we take one step further to identify the "anomalies" of urban sustainability among the 100 UAs for each dimension and on the whole as multi-dimensional coupled infrastructure systems. Results show: (1) urban population of the 100 UAs increased by 36% during 2000-2020; (2) urban slums occurred in 85% of 34 examined UAs in the Global South; (3) urban greenness declined in the 100 UAs by 8% during 2000-2019; and (4) 79% of the 100 UAs were projected to have less than 30 EHDs per year during 2021-2030. Our findings provide global baselines for place-based problem-driven policymaking for the examined UAs and suggest improving urban green infrastructure as their top policy imperative. Our findings point to a critical research gap in the urban sustainability literature: Studying sustainability transitions of the "abnormally" sustainable UAs identified in this study that had exceptional performances on the four examined sustainability dimensions, e.g., Beijing of China and Milan of Italy.

Urbanisation-driven land degradation and socioeconomic challenges in peri-urban areas: Insights from Southern Europe

Climate change and landscape transformation have led to rapid expansion of peri-urban areas globally, representing new 'laboratories' for the study of human-nature relationships aiming at land degradation management. This paper contributes to the debate on human-driven land degradation processes by highlighting how natural and socioeconomic forces trigger soil depletion and environmental degradation in peri-urban areas. The aim was to classify and synthesise the interactions of urbanisation-driven factors with direct or indirect, on-site or off-site, and short-term or century-scale impacts on land degradation, focussing on Southern Europe as a paradigmatic case to address this issue. Assuming complex and multifaceted interactions among influencing factors, a relevant contribution to land degradation was shown to derive from socioeconomic drivers, the most important of which were population growth and urban sprawl. Viewing peri-urban areas as socio-environmental systems adapting to intense socioeconomic transformations, these factors were identified as forming complex environmental 'syndromes' driven by urbanisation. Based on this classification, we suggested three key measures to support future land management in Southern European peri-urban areas.

Greening the city: Thriving for biodiversity and sustainability

Urban population and urbanisation are increasing rapidly, mainly in developing countries, usually at the expense of green and blue areas. This trend will decrease the ecosystems' capacity to supply ecosystem services (ES) and threaten human wellbeing. Therefore, it is key to establish greening policies in urbanising areas, which are essential to improve the liveability of cities. Restoring and developing green and blue infrastructures using nature-based solutions is vital to improving urban biodiversity and urban ecosystems. Healthy urban ecosystems have a high capacity to supply regulating (e.g., air, noise, climate and water regulation), provisioning (e.g., food, medicinal plants, biomass) and cultural (e.g., recreation, landscape aesthetics, social cohesion) ES. This multifunctionality can provide diverse environmental, social and economic benefits to urban residents, hence contributing to the sustainability of urban areas. However, urban green and blue areas are also associated with ecosystem disservices (e.g., plant allergies or poisoning, emission of biogenic volatile organic compounds, unpleasant smells), tradeoffs (e.g., increased water consumption, wildfire risk, associated management costs) and implementation barriers (e.g., political motivation, lack of knowledge, time and workload). Overall, the SI published 8 articles from different parts of the world, such as China, the USA, Italy or Spain, focused on important aspects of greening the city (e.g., green roofs, green walls, green infrastructures, sustainable mobility).

Taxonomy and model for valuing the contribution of digital water meters to sustainability objectives

Water security is an issue across the world as communities face ageing infrastructure, population increases and climate change. The application of digital water metering (DWM) to properties has had a demonstrable impact on water savings at the property and network levels, on efficiencies within water utilities, as well as on improvements to customer satisfaction scores. Gathering and processing near-real-time water usage data is very important for both end-users and utilities, as well as demand and supply management planning. The potential contribution of DWM to the three pillars of water sustainability (environmental, economic development and social equity) is often overlooked. In Australia and other jurisdictions water utilities are facing up to the challenge of climate change. However, business cases promoting DWM are often unsuccessful because the benefit side falls short of the cost side. This study sought to identify possible DWM benefits not previously considered through an extensive review of academic and industry literature, and then to view those benefits through the lens of sustainability. The 77 identified benefits of DWM were catalogued and a taxonomy was created. The study elicited the opinions of experts, before quantifying them, thus identifying two distinct contexts of benefit value; subsequently, it surveyed the views of customers and developed a stochastic model of benefit value. The model, named DWM360, was applied to the project data of a large metropolitan water utility in Australia to model their DWM proposal for cost savings, contribution to sustainability and uplift in customer satisfaction. This paper presents a novel focus on how the benefits of DWM assist water sustainability. It considers differing social norms that impact consumer acceptance of changes in metering and water charges. The study will be of interest to researchers as well as practitioners looking to identify sustainability aspects of DWM.