NBS or ‘nature-based solutions’ denote the means for the provision of services, processes and outcomes supported by nature. NBS is characterized as a compound term, where ‘nature-based’ describes a kind and ‘solution’ refers to its main problem-solving feature. NBS and water share a deep multi-facetted interconnection, the relevance of which in the peri-urban context is crucial but often overlooked.
NBS is an umbrella concept which can be aimed to support the achievement of society’s development goals and safeguard human well-being in ways that reflect cultural and societal values and enhance the resilience of ecosystems, their capacity for renewal and the provision of services.these are designed to address societal challenges such as climate change, food security or natural disasters. According to a report published by IUCN (2016), NBS embrace nature conservation norms and principles; can be implemented alone or in an integrated manner with other solutions to societal challenges (e.g. technological and engineering solutions); are determined by site-specific natural and cultural contexts that include traditional, local and scientific knowledge; produce societal benefits in a fair and equitable way, in a manner that promotes transparency and broad participation; and maintain biological and cultural diversity and the ability of ecosystems to evolve over time. Further, these are applied at a landscape scale; and recognise and address the trade-offs between the production of a few immediate economic benefits for development, and future options for the production of the full range of ecosystems services. Two core definitions that describe the concept are as follows:
By their basic nature, NBS and water are closely interconnected. As described by the United Nations World Water Development Report 2018, the physical, chemical and biological properties of ecosystems affect all the hydrological pathways in the water cycle. Plants affect water availability and climate through transpiration functions. Plant roots contribute to soil structure and health and hence influence soil water storage/availability, infiltration and percolation to groundwater.
Further, how much water infiltrates, evaporates from or percolates through land depends also on the geometry of the soil pore space, and therefore on soil structure. Moreover, the conditions at the soil surface (vegetation cover, soil structure, etc.) control the partitioning of rainfall into surface runoff and infiltration. Ecosystems make important contributions to precipitation recycling from local to continental scales. It is now contended that instead of being regarded as a ‘consumer’ of water, vegetation should perhaps more appropriately be viewed as a water ‘recycler’. Vegetation removal probably has the most severe impacts on rainfall in drier areas, contributing to increased water scarcity, land degradation and desertification in those areas.
The water-related processes and functions of ecosystems are managed to deliver benefits to people as ‘ecosystem services’. While all ecosystem services are dependent on water, there are specific ecosystem services that directly influence the availability and quality of water. Together these underpin the three dimensions of water resources challenges, namely, water availability (supply or quantity), water quality and moderating risk and extremes (including water-related disaster risk).
NBS usually offer multiple water-related benefits and often help address water quantity, quality and risks simultaneously. In addition, these also often offer co-benefits beyond water-related ecosystem services. For example, ecosystem creation or restoration can additionally create or improve fisheries, timber and non-timber forest resources, biodiversity, landscape values and cultural and recreational services, which in turn can lead to added socio-economic benefits. An overall key advantage of NBS is that they contribute to building overall system resilience.
The concept of ‘peri-urban’ is linked to the process of urbanization. Thus, the peri-urbanisation process is a context that prioritizes the place-based dynamics and consequently, the peri-urban context becomes highly relevant for the potential NBS due to the following aspects:
The process of peri-urbanisation has been found to be divergent across the countries. For example, in developed countries, peri-urban growth is linked to urban welfare and well-being—e.g., providing rural retreat, recreational values, and aesthetics. Whereas in developing countries such growth is viewed as an urban management mire—e.g., poor landscape integrity, a lower standard of living, disposal of solid and toxic wastes sites.
Despite the varied patterns, on the whole, urban expansion to peri-urban areas often poses numerous landscape management challenges, e.g., loss of agricultural land, fragmented landscapes, destruction of biodiversity habitats, and decline in ecosystem services. Peri-urban areas are also vulnerable to the climate change phenomena. Given the close interconnection between NBS and water, continual urban encroachment to peri-urban areas coupled with the potential impacts of climate change—can potentially deepen water challenges in the peri-urban – in terms of water availability, water quality as well as risk and extremes. Additionally, given the interconnections and inter-dependencies between the urban and peri-urban spaces and communities, degraded hydrology and hydrodynamics in the peri-urban can in turn pose challenge to water management in the urban core.