3.2.2. From Grey Literature

The most structured recommendations in grey literature on how to address climate change in the design of cities, their relationship to water, and in some cases with risk, have been promoted through organisations such as the International Water Association (IWA (International Water Association), 2016), the World Bank [26,54], or the United Nations [28], among others. They are presented in the form of multi-stage frameworks that help build the response of cities and territories to the challenges of climate change, particularly in water systems. The methodologies and practices that stand out from the grey literature are shown in Table 3:

**Table 3.** Structured recommendations from grey literature.


#### **Table 3.** *Cont.*


This sub-section presented the status quo of the world's best-structured practical references in this field. It aimed to outline if their approaches complement those of the scientific literature referred to in the previous section. Further research could also help to assess how the scientific literature validates the grey literature.

#### *3.3. Approaches to Climate Change Adaptation of Water Utilities and City Planning*

Since the 19th century, water infrastructure has been centrally built to address hygiene and health issues, significantly reducing diseases and increasing health [56]. Centralised systems, the norm in cities, are characterised by extensive treatment, distribution, and collection facilities for treatment that connect distant points of origin/rejection and their final consumers [57]. Most developed countries spend between 1% and 6% of their annual GDP on centralised systems [58], resulting in substantial "sunken costs" and total dependence on water services (by nature with great inertia). Consequently, they face a blocking situation in which transforming alternatives for water management encounter barriers to entry [59].

These very centralised systems are based on mainly buried infrastructures whose main objective is to reach the water to citizens in quality and quantity, drain and treat the effluents generated, and drive rainwater as quickly as possible out of urban areas. Often, these infrastructures lead water from distant regions to the populations that need it through systems that favour the reliability and quality of the water supplied [31]. Similarly, treated effluents are often rejected from their place of production in large wastewater treatment

plants. The dimensioning of these infrastructures is made for a distant design horizon with high initial sunken costs [10], which, in most cases, implies large tariffs for the first generations that use them and an idle capacity for at least the first years of activity [10]. This means a consequent waste of financial and operational resources, considering the need to "move" high water resources out of their natural "habitat", with impacts that go far beyond your place of consumption [31].

On the one hand, floods often involve the routing (undue if in separative networks) of rainwater to wastewater collectors, thus implying discharge into the water environment and in an uncontrolled form of crude effluent, more or less diluted. Besides this impact on the environment, floods also entail increasing human and property damage to which the current paradigm cannot respond, not only in developing countries (for instance, Mozambique and Pakistan) but also in developed countries, of which the 2021 floods in Germany are a recent example [60]. On the other hand, it is neither technical nor economically feasible [10,19]) to size wastewater and rainwater infrastructure for all extreme situations that potentially occur.

Concerning water scarcity, despite growing awareness of the effects of climate change, the transformative process of water management to include new sources (such as water reuse, rain harvesting, or desalination) or new conceptions (such as decentralised systems, green and blue infrastructures, etc.) is confronted with several obstacles that still lead to some inertia [32]. It should be said, however, that this latent stagnation is primarily presented by the incumbents, which present, among others, barriers to the implementation of innovative measures such as [32]: greater reliability (general) of centralised water systems, potentially lower costs of centralised systems (more significant economies of scale), perception of greater risk to public health by consumers, legislation not yet fully adequate for water reuse, uncertainties regarding the governance of the different systems in the future, and the lack of motivation in the entities that manage the status quo. This "lock-in" effect [61,62] is associated with apparent economies of scale, progress in the "learning curve", confidence in existing technologies, and network economies (agents using the same technology as their peers) [31], which translates into a barrier to innovation and the entry of more sustainable systems, perpetuating the incumbent.

However, there are also crucial motivations that lead to transformative processes in the relationship between urban water management and urban planning, such as [32,63,64]: the need to resize cities according to the variation of their population and consequent increase in consumption; public perception of the waste of the use of drinking water for irrigation, flushing of toilets, and washes; climate change, with a particular focus on capturing/deferring rainwater runoff and managing water scarcity; food security, as the lack of water, together with the degradation of agricultural land, leads to a reduction in agricultural productivity, which in turn leads to lower incomes and food availability [6,65]; increased consumption and decreased availability motivated by the average and "peak" increase in temperatures; sensitivity to phenomena such as self-sufficiency and the circularity of the economy. Naturally, in very concrete geographies, extreme phenomena of lack or excess of water are already the biggest catalysts for this paradigm shift, such as the cases of Israel, China, Australia, California, and Singapore, to report the most studied [66–68]. Thus, even in well-established and proven systems, the need for reinvestment, the urgent response to climate change, and the dynamics of urban expansion force a paradigm shift, which becomes necessary, both in underdeveloped countries and in developed countries.

For their part, in underdeveloped countries, in addition to drivers related to climate change and population growth, high rates of urban growth, poor trust in institutions [69], and uncertainty about city planning, combined with a lack of initial capital and high discount rates, lead to the trend of investing in rapid implementation solutions and in turn to a strong tendency to avoid significant investments in infrastructure [70].

The progressive hybridisation of centralised and decentralised systems has been reported as the most likely trend of implementation, combining the reliability and financial sustainability of centralised systems, so-called conventional, with the need to adapt cities to climate and demographic change, thus ensuring greater resilience. In this context, there is room for more consolidated studies, particularly about both levels' systemic and parallel functioning [32]. As such, the challenges presented above require different approaches and paradigms.

The way literature faces these challenges can unfold systematically in the following vectors: operational, organisational, institutional, behavioural, economical, technological, and urban planning.

Concerning the operational vector, the scientific literature points towards the definition of strategies to save water, reduce losses [10], minimise undue inflows to urban systems, and separate the sanitation of wastewater and rainwater [33,42] and the use of stored rainwater in periods of lower rainfall [71], either in a single-family management analysis [33] or in a city-level or basin-level approach [71,72]. Of course, some of these operational interventions must be integrated with the necessary investments corresponding to the economic and technological vectors.

At the organisational vector, the tendency referred to in the literature is for decentralising infrastructures and systems, corresponding to their greater spraying. The challenge arises regarding their management—in the local community, municipal, or WSPs—and, in any case, how centralised and open to citizen participation is. Questions are raised, as to how the "water decentralised infrastructures" should be created, given the technologically premature state of the proposed solutions and information regarding exploration costs, monitoring of their performance, and diffuse responsibility regarding their current management [31,44].

At the institutional level, efforts focus on sharing objectives and knowledge, usually with very flexible approaches, involving various stakeholders at national, regional, and local decision-making levels. At the economic vector, no direct savings in technical solutions related to sustainable water management are evident [31], especially considering the energy and operating and maintenance costs accompanying solutions such as desalination [35], rainwater harvesting [33,73], or reused water [32,74], where the "scale" factor is essential.

Concerning the behaviour of the final consumer, studies have been presented in Israel that correlate their perception of those reuses with their level of treatment, their possibility of use, and other variables, such as education and age [68,75]. The desire to consume alternative sources of water and the way the message is passed are fundamental aspects of its implementation [68,76]. However, some 13% of the consumers in a study conducted in the United States rejected the use of recycled water, depreciatingly called "from the toilet to tap" by those opposing it [77].

At the technological vector, the main trends concerning the challenges in the urban water sector for the 21st century are related to (i) the increased use of alternative sources of water, namely the reuse of rainwater [33,62,73,78], the reuse of water (direct or indirect), and desalination and the new technologies related to it that arise (Larsen et al., 2016); (ii) the "buffering" of extreme phenomena (usually related to floods) [8,42,62,79] in the search for more sustainable solutions with positive environmental externalities [35,68,80–82], such as Sponge Cities in China, greenfield expansions in Australia or redevelopment in the Netherlands [8,22,53,83]; and (iii) the application of information technologies to the planning of the urban cycle of water and cities [79,84,85]. Considering the various drivers referred to above, which influence the relationship between the sustainability of the management of urban water resources in the face of the challenges of climate change, population growth, and increasing urbanisation, growing literature is addressing the use of artificial intelligence to integrate the diversity of inputs. This literature seeks to integrate more technical and socio-economic baseline data, such as spatial planning, localisation of water infrastructures, impermeable surfaces, green areas, and green roof areas, among many others [38,84] to understand the practical implications that the future provides, depending on the simulated scenario. In a more focused way, several studies model and project the various possibilities of water reuse [86], rainwater reuse [73], or the behaviour of watersheds in extreme situations [87], among many others.

Finally, the scientific literature related to urban planning focuses on how positive externalities can be obtained in the pursuit of sustainable solutions that allow cities to tackle climate change ([20,22,30,71,88]. These analyses have focused on the preparation of cities for the management of water retaining [18,20] by defining the constructive details to be implemented in public/private infrastructures (porous pavements, green roofs, etc.) [42,64], by xeriscaping [87], through integrative interventions at the neighbourhood level [83,84], by the adaptation of the blueprint of cities to help landscape management in prioritising urban development strategies in the water-energy nexus [87] and the significant transformations of expansion or adaptation of cities considering rainwater management [71]. London is a paradigmatic example in how it defines water neutrality as a concept to frame the water stress in cities, integrating spatial data with an integrated urban water management model; this holistic, systemic design framework is designated CityPlan-Water [38]. In Table 4 we summarize the vectors presented in Figure 4 with the approaches to tackle climate change and urbanisation in the water sector.


**Table 4.** Synthesis of the approaches to tackle climate change and urbanisation in the water sector.

The table above shows the main references found for each vector, outlining the limited number of those dealing with the relationship between the entities that manage the water services and the territory.

**Figure 4.** Main vectors contributing to the urban water management adaptation to climate change, according to the literature review.

#### **4. Discussion**

Considering the results mentioned above, several issues can be highlighted concerning the relationship between sustainable water management, urban planning, and climate change. In fact, despite the lack of practical implementation that does not yet follow the diversity of existing scientific literature on the sustainable management of the urban water cycle [38], it already presents a set of learnings/outcomes and gaps that allow us to perceive the main insights and the gaps to be filled.

One conclusion to be withdrawn from the outset is that the most significant innovations or need for innovation are mainly at the organisational and economic vectors and in the relationship between the various stakeholders and citizens/consumers and not so much in terms of technological development since the main drivers for change still arise in the paradigm shift from centralised to decentralised systems and how to share their management with the other stakeholders, including entities that manage the territory. Although there is a trend in the literature towards responding to climate change through decentralised systems, some of the best examples of success in adapting to climate change in the water supply sector, especially in terms of water reuse, occur using concepts of centralised systems, such as Singapore, Israel, or Southern California in the US.

Of course, in situations where redundancy exists, i.e., where centralised infrastructure remains a "last resort", there may be double pricing to sustain the sunken costs related to that system and the capital and operating cost tariffs associated with more sustainable methods. There is a need for a broader cost–benefit analysis involving not only the financial aspects but also the positive/negative externalities resulting from the implementation of more "sustainable systems" [76,94].

It is important to remark that the relationship between urban planning, WSPs, and climate change has also focused on flood control and less on water supply. There is, therefore, a gap in the need for scientific development [30,100]. This gap significantly increases when it comes to the integrated management of both "too much" or "too little" water, i.e., flood control and water supply.

For that matter, WSPs are facing increasing challenges in terms of water availability, management of consumption patterns, and the need for increased efficiency, which are alternatives to be developed to address the problem of lack of water [62], here still in the context of water directly collected from the water environment.

The planning of water infrastructures tends to be subordinate dweller to the planning of the territory [20] in a way that, in addition to being technically challenging, has also demonstrated other types of problems, such as complex collaboration in the face of more controversial situations of land use. On the other hand, the unavailability of staff in smaller locations and a level of diffuse responsibilities within and between each side, urban planning and WSPs, tend to hinder the necessary convergence. [20]. Adapting to a changing climate requires the collaboration of the disciplines of spatial planning and urban water supply management [30].

Many arguments and practices associated with concrete cases of articulation between WSPs and those that manage the territory can also be applied to the water supply strand. Consolidating a projection of the future—a practice to which urban planning is dedicated—with the projection of climate change is pointed out as being the way forward, to which the necessary articulation with the drainage and water supply strands of the WSPs is added.

Some of the barriers to overcome in the water sector are related to the "lock-in" effect related to the already mentioned inertia derived from the sector, often resonating on buried infrastructure with an extensive lifetime and high capital costs. On the other hand, it is a sector traditionally averse to innovation [10,76], both technical and operational [31]. The main insights and gaps that stand out from the literature are presented in Table 5, following Figure 4.


**Table 5.** Synthesis of the main insights and gaps that arise from the literature review.

#### **Table 5.** *Cont.*



very promising in the fields of desalination and water reuse [95–97,108].

**Table 5.** *Cont.*



The table above systematises the existing insights and gaps, constituting a basis for future integrated or vector-focused studies.

#### **5. Conclusions**

Through a literature review, this paper systematised the main concepts involving urban planning and the sustainable management of urban water (SUWM) in a context of demographic, urban, and climate change, as well as the way the scientific community interprets and tackles these challenges.

It noted an increasing concern for climate change in the context of the urban water cycle and urban management, mainly concerning flood control and not so much about cities' preparation for scarcity and water savings. Studies addressing the maximisation of water resources were also noticeable but fewer about control and management of demand. It is also perceived that the growth and adaptation of urban water systems cannot continue to be done incrementally, as it has been so far.

Knowledge deepening is required in the technical and economic evaluation of the overarching concept of SUWM systems in a way that integrates values beyond financial matters and introduces an accurate cost–benefit analysis of the solutions for society. New forms of growth, contemplating a hybridisation of systems (centralised systems that grow in a decentralised way), imply new paradigms of assessment, management, and collection of tariffs for which more consolidated knowledge is required.

Achieving synergies and economies of scale, in the panorama of cities, for systems of rainwater harvesting and water reuse are presented as themes in need of development, in particular in the way they can involve the planning of cities and their stakeholders, not only from a design perspective but also in its management, decision making, and in the preparation of the final consumer for the "new water" that can be used in a context increasingly focused on the circular economy.

The grey literature produced by international organisations has complemented the scientific literature by presenting frameworks for some of these measures that will allow the various stakeholders to consider infrastructure planning in the context of climate change according to risk.

There is also a clear need for further studies and practice on the relationship between the various actors, particularly those managing the territory and water services, towards a collaborative response to the challenges of climate change. Despite the evident constraints, yes, adapting together is possible and desirable. Further research is required, though, to clarify the design of the new institutional bridges, necessary steps, and means.

**Author Contributions:** Conceptualisation, V.V., T.F. and A.L.; methodology, V.V.; validation, V.V., T.F. and A.L.; formal analysis, V.V.; investigation, V.V.; writing—original draft preparation, V.V.; writing—review and editing, V.V., T.F. and A.L.; supervision, T.F. and A.L. All authors have read and agreed to the published version of the manuscript.

**Funding:** This research received no external funding.

**Data Availability Statement:** All the data is available within this manuscript.

**Acknowledgments:** The authors are grateful to Águas de Portugal Group and the University of Aveiro for supporting this research.

**Conflicts of Interest:** The authors declare no conflict of interest.

#### **References**


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