of people living in urban areas, food wastage can increase urban food prices and greenhouse gas emissions as wasted food decomposes in landfills. It also indirectly contributes to habitat loss, since more land is needed for food production, and fertilizers, other inputs and fuel for transportation are wasted. Since food systems are directly or indirectly connected to all 17 SDGs, urban lifestyles and patterns of consumption can affect both sustainable development outcomes and the global climate, especially for the developing world. Many cities are promoting urban agriculture with the potential to significantly reduce the urban ecological footprint and increase food security (Corbould 2013). However, the form this takes (vertical farms, small community farms, etc.) depends on the context of individual cities (Opitz et al. 2016; Clinton et al. 2018; Azunre et al. 2019; Edmondson et al. 2020; see also section 5.2.2).


Land-use and land-cover changes and other transformations due to urban expansion (ECJRC 2018) and the resource requirements of cities are occurring at the expense of fertile soils and forest cover, further stressing food security (Güneralp et al. 2020) and the loss of ecosystem services (for example, regulation of water and air quality, habitat conservation and carbon storage) (Xie et al. 2018). There is an urgent need to understand the trade-offs between the different urban expansion models before committing to largely irreversible changes (Pols and Romijn 2017).


Many countries, especially in the Global South, are also experiencing unplanned urban expansion, through informal settlements, often on environmentally sensitive


Table 3.1: Knowns and unknowns at the city scale


Environmental dimension


Air What we know


While certain parts of the world are improving air quality, in many cities it is deteriorating and exceeds WHO guidelines for PM2.5


and NO2 and PM10 . Together with


greenhouse gases, non-climate air pollutants strongly affect air quality in urban centres. Particulate matter (PM2.5


), alongside some toxic chemicals,


are the biggest environmental health risk factor, while ultrafine particles in vehicle exhaust emissions are a source of increasing public health concern in cities. These exposures have a negative impact on the health of urban populations. Poor air quality is caused by anthropogenic and natural emissions of air pollutants from local and regional sources and the formation of secondary pollutants in the atmosphere. This includes global and long-range transport of air pollution. The continued increase in CO2


and other greenhouse


gas emissions and the resulting atmospheric concentration translates into extreme heatwaves, increased droughts and precipitation deficits, flooding and increased precipitation, and rising sea levels in coastal cities (IPCC 2018). COVID-19 is a unique opportunity to study the short- and long-term impacts of reduced emissions on air quality and climate change. This will likely influence mitigation strategies in the future.


Remaining gaps in knowledge


Air quality monitoring is limited in many low- and middle-income cities (as well as in some high-income ones), hindering proper air quality assessments. In some cities, there is no monitoring data at all. Satellite monitoring data such as the Copernicus Atmosphere Monitoring Service can help fill gaps. In addition to air quality monitoring, emissions inventories and air quality modelling are needed in lower-income countries to understand the sources and impacts of emissions. Integrated urban hydrometeorological, climate and environmental systems and services are needed and the full spectrum and complexity of urban hydrometeorological and climate hazards need to be considered (WMO 2019a).


The methodology for calculating air quality indicators, such as indexes, needs to be standardized globally. Better air pollution epidemiology and the attribution of specific pollutants to disease burden in the urban centres is needed to allow decision makers to target the reduction of specific air pollutants to reduce health impacts. Monitoring and emission inventories are essential for common air pollutants and priority chemicals, such as toxic trace metals and cancerogenic and mutagenic polycyclic aromatic hydrocarbons.


Detailed climate change models are needed at the city level to provide better information on potential impacts.


and vulnerable locations such as slopes, flood plains and wetlands. Human-generated waste in such unplanned developments further pollutes water and soil due to the lack of adequate waste management systems and the increasing the area of unregulated landfills (UNEP 2015; UNEP 2019; Satterthwaite et al. 2020). These encroachments destroy and fragment critical habitats. including those of surrounding wildlife, and may cause conflict between humans and wildlife.


3.4 Data and information needs on the state and trends of the environment at the city scale


The previous sections highlighted two critical aspects of urban settlements: firstly, how cities are both affected by and contribute to environmental change; and secondly, how the impacts of environmental change are interconnected and experienced in different ways in different locations (even within the city). Table 3.1 highlights the relationship between the current environmental state and trends at the city scale and the corresponding data and information needs for decision makers and researchers to be able to better track progress on the important transformations that are needed. The table highlights some of the main data and information gaps related to the urban environment. Filling these gaps is paramount for environmental management, since this will provide valuable information on the interlinkages across the different environmental dimensions (air, biodiversity, freshwater, oceans and coasts, land and soil) and between people and the environment (UNEP 2019, chapter 3).


54


GEO for Cities


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