Evolutionary urban resilience as an incremental approach to sustainability: a multifunctional pluvial flood and wastewater risk reduction framework

After the increasing climate change and fast urbanization adverse effects on pluvial floods, in addition to the freshwater resources’ shortage risk, transversal urban solutions need to be tackled. This paper focuses on how the evolutionary urban resilience practices (along with the nature-based solutions and climate change adaptation) work as an integrated approach to enhance multifunctionality levels of sustainable urban planning and design. This integration eventually leads to more pluvial flood-resilient cities and more sustainable urban water resources simultaneously. After thoroughly analyzing related literature and best practices using descriptional, comparative, and statistical approaches, a proposed risk reduction framework that facilitates the resilience operationalizing process was formulated. The proposed framework introduces a design equation that measures the relationship between sustainability and urban resilience sectors. In addition to that, prioritized strategies for enhancing flood resilience and urban wastewater management within the Egyptian local scale were ranked for future applications.

Among several flood triggers (Fig. 2), climate change is expected to increase their frequency and severity, affecting highly exposed cities, such as those in deltas and lowelevation coastal zones. Besides climate, the urbanism factors participate in urban waterrelated hazards and specifically trigger pluvial floods. Factors like "maladaptive drainage systems" and "insufficient stormwater discharge, " along with "gray construction overuse, " cause the removal of natural rainwater-retaining and recycling infrastructure [1].
During the last decades, the focus on reducing floods was manifested in risk management frames, but nowadays, several objectives need to be met for water quantity/quality  enhancement and rainwater recycling to approach sustainability. Since the current centralized urban drainage models became insufficient due to climate change, urbanization, and social circumstances constraints [1], other contemporary multifunctional strategies which consider nature and multi-discipline integrations are a must. An example of these integrations is a disaster risk reduction (DRR), climate change adaptation (CCA), and integrated urban water management (IUWM) within multi-scale planning and implementation framework (since hydro-meteorological risks and climate change negatively promote each other) [2]. Accordingly, the "resilience" term is gaining uprising significance even more than before as a contemporary integrated resolution for cities' vulnerability state. Resilience is a suitable approach to deal with "shocks" and "stresses" in cities since it's a function of "dynamic-complex" systems, which are presented the best within the city morphology. As of 2020, approximately 85 cities have national resilience policies. Due to its wide range of interrelations (physical, psychological, ecological, social, economic, individual, technical), resilience is a widely preferred approach in the various city development sectors for a while now, often interchangeably or inclusively with sustainability.

Rationale and scope
The study aims to explore the evolutionary resilience and nature-based solutions multifunctionality, to address Egypt's urban water stresses, within a sustainable and integrated urban development framework. This comes as a crucial adapting and preparation responding strategy to the current pluvial flood risks, and the upcoming freshwater shortage. For a conceptual scope, see Fig. 3.

Methods
A mixed approach of qualitative and quantitative methods was adopted throughout the study outline (Fig. 4). To develop the theoretical framework, qualitative processing included an inductive and analytical review of related literature on the background and traditional solutions of current urbanism, climate, and resource risks.  Then, the literature explored the role of resilience in sustainable urbanism, followed by studying the resilience concept and its interrelated disciplines. Combining the understanding of resilience capacities with the obtained knowledge on flood risk management led to a closer look at synergies between resilience and sustainability. These interactions led to thematic dimensions of resilience standards, which were focused on through the ten best practices of descriptive-analytical study. Case studies from different countries were chosen to reflect a wider range of urban resilience practices in both flood risk management and sustainable urban water management after or before severe damage of a crisis. The detailed descriptive study provided a clear vision of the resilience concept applicability and operationalizing within urban systems that seek sustainable practices. Conclusions on the relevance of multifunctional resilience for urban water and flood risk management through sustainable integrated urbanism were extracted for the specific case-study areas and in general. These indicators took the form of preliminary resilience framework pillars with proposed application strategies on the national scale. After that, quantitative processing of the proposed framework was conducted through field interviews and an online questionnaire. The results were statistically analyzed to deduct the finalized multifunctional urban resilience framework, based on the Egyptian urbanism variables. Primary data such as online questionnaires and interviews with experts were processed, besides secondary data (books, global organizations handbooks, national current profile statistics, international protocols, papers/articles, academic thesis, and websites).

Traditional risk management and alternative resolutions
In the 1960s, non-structural measures (warning systems, floodplain zoning, local floodproofing, and flood insurance programs) began to receive more attention while the appreciation of embankments degraded [3]. Using classic flood control measures  only became an inadequate response to the growing risks [4,5]. Therefore, more efficiency was detected in alternative concepts that focused on the integration between structural and nonstructural measures and land/water management [6,7]. Such holistic approaches are a shift from purely sectoral water management to more integrating urban planning wherewithal to separate vulnerable land uses from flood-prone areas. Hence, the resilience concept is a promising framework to merge the risks and uncertainties within planning [8], as Table 1 indicates. In 1994, resilience officially broke into the disaster field in the Guidelines for the World Conference on Natural Disaster reduction.
The resilience approach is mainly about handling undesired change, as it investigates the best management frameworks of interacting systems within cities. Urban resilience is "The capacity of all the city systems-individuals, communities, institutions, businesses-to survive, adapt, and grow, no matter what stresses and shocks they face" [10]. Table 2 summarizes urban resilience basic capacities, and Fig. 5 illustrates resilient and vulnerable cities' comparison.

Resilience and sustainability
Recently, the resilience term was used widely as an updated version of sustainability, which is controversial since the two concepts are different in many ways. Sustainability observes the global resources levels, which would be a failure without building resilient societies against natural hazards and making sure that future development does not reinforce the vulnerability [14]. Table 3 compares the basic properties of the two concepts.
In 2014, the Hyogo Framework for Action assured that "sustainable development demands future risks prevention and current risks reduction" [16], which is relative to the "Sendai Framework for DRR" recommendations, and the New Urban Agenda guidelines. Later, the sustainable development literature framed resilience as a fixed goal among the acknowledged 17 sustainable development goals SDGs and subtargets in many sectors (goals 9,11,13,14).

Evolutionary urban resilience
Since resilience thinking is an interdisciplinary approach to city planning [17], planning for resilience, therefore, bridges the environmental, social, and economic resilience aspects in spatial planning [18]. Literature diverges into three main approaches  Buffering: over-dimensioning system capacity for more disturbance absorbing. Ex: "water/ public squares, " arterial roads elevating to function in floods, risk-prone areas with rapidly changing functions Recovery Flatness: response rapidity and flexible participation empowering. Ex: locals' self-reliance/ self-organization High flux: resources fast mobilization. Ex: early warning system and recovery materials' rapid accessibility Adapting Including flexibility, and learning The "4Rs" [12] Robustness (ability to withstand a shock), Redundancy (functional diversity), Resourcefulness (ability to mobilize when threatened), Rapidity (ability to contain losses and recover promptly) [13] Flexibility: rearranging the ability of structure/functions when disturbed. Coordination: needed to make the best use of resources by decision-makers, citizens, and planners. Independence: needed self-reliance to survive adversities. Connectivity: interactions with other systems on a broader scale. Collaboration: inclusive and bottom-up urban management approach. Self-organization: establishing community-based activities via social institutions and networks. Efficiency: developing strategies to maximize benefits  in terms of planning for resilience: new eco-towns, strategic navigation, and evolutionary approach. The evolutionary literature framework is concerned with interlinkages between preparedness, persistence, adaptability, and transformability over multi-scales/ timeframes in which communities' role is central due to their learning, innovating, and changing capacity [19]. According to [18], the evolutionary perspective is the most comprehensive approach among these three resilience planning perspectives. The overall resilience aspects of this research are summarized in Fig. 6.

Nature-based solution approaches
Nature-based solutions are integrated urban water systems, summarized in Table 4, which target drainage landscapes and structures to achieve multifunctionality and ecosystem services provision. They also enhance drainage during design storm events (see Fig. 7).

Best practises' analytical summary
The descriptive approach of 10 best practices (Fig. 8) was a diagnostic tool of the past and current resilience applications, from which preliminary resilience framework pillars with proposed application strategies were deducted. The analysis included cities with varied spatial, institutional, and urban contexts, such as New Cairo, Amman, Casablanca, Hamburg, Sponge Cities, Santa Fe, Alba Iulia, Semarang, Dhaka, and Accra. Several practices of these cities were studied to spot general vulnerabilities that hinder the resilience implementation, make the best use of the relevant approaches as inspiration for our local resilience base to be, and reflect the role of integrated urban planning within the evolutionary resilience frames. Reviewed aspects included risk and vulnerability contexts, past management approaches, current resilience planning, and nature-based measures. On a global scale, resilience practices of Santa Fe city, for instance, were effective from a social-institutional approach, while in Hamburg, the physical-environmental approach had an outstanding impact. A summarized analytical matrix of best practices is attached in Additional file 1.  Egypt's national and local profile of water-related stresses reflected several risks and vulnerabilities that need to be addressed within integrated and resilient measures, such as the following: 1. "High-risk" flood classification due to increasing severity and frequency of current pluvial floods and future sea-level rise-based coastal floods [25,26]. 2. Water scarcity and droughts are a future risk due to Nile river political disruptions [27] and high evaporation rates with changing precipitation patterns according to IPCC literature. 3. Rapid urbanization with weak risk-informed land use planning and inadequate enforcement of sustainable design and green building codes. The following preliminary resilience framework pillars were deducted as prioritized pillars within the urban resilience enhancement process. These umbrella pillars and their initial branches have dramatically participated in the best practices' overall success and failure assessments: 1-Evolutionary resilience approach 2-Nature-based solutions and infrastructures 3-Governance and institutional capacities 4-Resources 5-Social capital and participation 6-Multi-risk-informed decision making 7-Critical infrastructure efficiency

Developing resilience strategy matrix
The previously deducted indicators of case-study analysis included applied global and regional resilience strategies. Due to the wide previous literature spectrum, selecting key representative strategies to enhance urban resilience for pluvial floods and stormwater wasting is a complex process that depends on relativity to research objectives and applicability scale within the local climate. The following matrix in Fig. 9 indicates the selected strategies, formed through 4 complex urban resilience dimensions. These dimensions profile the urban system aspects and contain strategic target clusters. The detailed implementation strategies matrix is modified using excel to end

Collecting and processing primary data
To address the research hypothesis, and adjust the proposed resilience strategies to the local and national application, two primary quantitative data sources were approached: pre-structured in-depth interviews and online questionnaires. They both targeted local officials, NGOs, private consultancy offices, and academics in urban planning and governance, infrastructural engineering, water resources, and environmental fields. The questionnaires and interviews also allowed respondents to assess the local and national performance on resilience. The questionnaire was structured into four sections: Section A, with 4 subsections representing the urban resilience sectors, had indicators with a 4-point Likert scale and aimed to measure the existing degree of urban resilience strategies, and nature-based solutions and CCA measures (successfully applied around the world) within the Egyptian flood risk management and reduction schemes. Section B, with a 3-point Likert scale, aimed to measure the awareness of pluvial floods and freshwater shortage in Egypt, including the insufficiency of sectoral traditional solutions and the need for new inclusive and multifunctional ones. Section C was designed to measure to what extent it is necessary to seek the integration and multifunctionality of resilience planning and other sustainability aspects within Egyptian cities. Section D is a 1-7 ranking scale that explores the hinders to establishing sufficient pluvial flood resilience and sustainable water management frameworks in Egyptian cities. The questionnaire and interviews were conducted with 60 respondents to score the previous resilience strategy matrix. Google form technique was chosen to widen the responding experts' sample. The online questionnaire outputs were added to the interview responses and statistically analyzed using the SPSS to compare and rank them based on each weight and extract modified hierarchical multifunctional resilience strategies in addition to a resilience-sustainability regression equation. The questionnaire form is attached in Additional file 2.

Reliability
The reliability and validity of each dimension measured in the questionnaire and interviews were tested, and all of the Cronbach's alpha coefficient values were greater than 0.70, while the values ranged between 0.86 and 0.98 in the validity test. The overall high-reliability ratios have increased the researcher's confidence level with the upcoming results. Table 5 summarizes general component score coefficient matrix results within factor analysis of the 6 tested dimensions:

Factor analysis
The above values indicate a significant relationship between each dimension's strategies, in addition to a strong expressing and measuring of the statements' latent variables, and suitable sampling adequacy.

Ranking analysis
The respondents' answers frequency on the hinders of "establishing sufficient pluvial flood resilience and sustainable water management frameworks in Egyptian cities" have been statistically weighted and ranked (Fig. 10). The highest hinder according to the sample was ranked (7), while the least one was ranked (1). According to this statistical ranking analysis, most respondents agreed on "lack of public awareness" as the biggest resilience sufficiency hinder, followed by "data insufficiency" and "limited application of monitoring, feedback, and maintenance concepts" respectively. Table 6 indicates some descriptive statistical measures for the main six dimensions of the questionnaire and interviews:

Descriptive analysis
The above values refer to the following: GI dimension The value of the arithmetic mean of responses with its standard deviation differs from the expected mean "3" of the 4-point Likert scale at a significant level of 1%, where the calculated T test value was greater than the tabulated value of 1.96. CV reflects a small degree of dispersion and a consensus and high tendency among respondents to the "uncertain" opinion, as a mean value, with (64.60%). Figure 11a shows the relative distribution of the sample responses to the (GI) strategies, where 32% of the sample went for "partially applied. " PE dimension Arithmetic mean of responses with its standard deviation differs from the expected mean "3" at a significant level of 1%, where the calculated T value was greater than the tabulated 2.58. The CV reflects a moderate degree of dispersion and a relatively high tendency to the "uncertain" opinion, as a mean value, with (55.44%). Figure 11b shows the relative distribution of the sample responses to the (PE) strategies, where 54% of the sample chose "unapplied. "

SE dimension
The arithmetic mean of responses with its standard deviation differs from the expected mean "3" of the 4-point Likert scale at a significant level of 1%, where the calculated T test value was greater than the tabulated value of 1.96. The CV reflects a moderate degree of dispersion and a relatively high tendency to "uncertain" opinion, as a mean value, with (55.09%). Figure 11c shows the relative distribution of the sample responses to the (SE) strategies, where 46% of the sample went for "unapplied. "

E dimension
The arithmetic mean of responses with its standard deviation differs from the expected mean "3" of the 4-point Likert scale at a significant level of 1%, where the calculated T test value was greater than the tabulated value of 2.58. The CV reflects a moderate degree of dispersion and a high tendency among the respondents to "uncertain" opinion, as a mean value, with (51.37%). Figure 11d shows the relative distribution of the sample responses to the (E) strategies, where 44% of the sample went for "unapplied. " 5th and 6th dimensions The values of arithmetic mean of responses differ from the expected mean "3" of the 3-point Likert scale at a significant level of 1%, where the calculated T test values were greater than the tabulated value of 2.33. The CV reflects a low degree of dispersion and indicates that there is a consensus and high tendency among the respondents to the "agree" opinion with +70%.
Prioritized implementation strategies Among 50 modified strategies of building and enhancing urban resilience towards pluvial floods and wastewater management, the statistical descriptive analysis indicated the prioritized strategies in each resilience dimension (based on the respondents' tendency mean values). These ranked strategies have the implementation priority to fulfill the indicated strategic objectives and resilience values in Table 7.

Resilience dimension correlation
A correlation test was conducted to measure the correlation degree between the main four adopted dimensions of resilience in the research, the following correlation matrix indicates the result ( Table 8): The table above shows that there is a significant correlation between the urban resilience sectors, where the highest correlation value of "0.851" was between the PE and SE dimensions, and the least correlation value of "0.727" between the PE and E dimensions. Table 9 indicates the R square analysis conducted to figure the relation between "sustainability, " as a dependent variable, and the four resilience dimensions (GI, PE, SE, E), as independent variables:

The coefficient of the model
From the above table, the coefficient of determination (R square) is equal to 1.000, and this indicates that the independent variables in the model (governance-institutional dimension, physical-environmental dimension, socio-economic dimension, energy dimension) explain 100.0% of any change in Sustainability. The model variables are statistically significant at a confidence level of 99%, so we accept the alternative hypothesis  that the independent variables have real value coefficients that are different from zero and they have a real impact on sustainability.

Regression equation
According to the previous R square test, a regression equation was formulated to describe the relationship between the four resilience dimensions and sustainable development, and figure out an index. It was found that: Sustainability "S" = ∑ (0.238*GI + 0.258*PE + 0.281*SE + 0.321*E).

Conclusions
❖ In this research, a detailed analysis of the worldwide applied resilience measures was conducted and compared to the national and local Egyptian scales. The output statistical figures also reflected the gaps and resilience hinders that need to be handled   for enhanced pluvial flood resilience and wastewater management at the local level. The data collection process and strategies also indicated the proposed stakeholders' structure who can direct the resilience planning and management wheel to make the best use of multifunctional benefits of flood resilience and nature-based solutions. ❖ The previously mentioned "preliminary urban resilience building pillars" were developed after considering the statistical analysis results to frame a multifunctional framework of urban resilience. This concluded framework includes major 10 indicators of establishing and enhancing the local pluvial flood resilience and wastewater management. It was derived from a detailed analysis of statistical indicators, in addition to the previous literature review and best practices. This framework provides the local urban governance entities with an integrated vision to work on the current pluvial flood resilience and wastewater management system through the following pillars (Fig. 12). ❖ The authors agree with previous studies which suggested that a resilient city is adaptive to chronic stresses and acute shocks without neglecting its essential functions in the middle of risk, which in our case are the pluvial floods and unsustainable wastewater management. It was also proved (inductively and statistically) that urban resilience works toward achieving the long-term sustainability targets, but it needs its overall sector performance and capacity, not just its ability to cope with pluvial floods and water scarcity hazards or its partial climate change adapting within sectoral and non-coordinated development frames. Additionally, the authors agree on the necessity of investigating wider areas of the research process for higher operationalizing levels of resilience and nature-based solutions concepts in Egyptian cities. Eventually, these previous conclusions addressed the research's main problem by applying multifunctional flood resilience and nature-based solutions within an integrated management framework. ❖ In addition to the experts' sample analysis, future work will include the social participation of locals in the research interviews and questionnaires. Additionally, testing the framework through a specified application on a specific local case will be considered, if suitable resources are provided.