A general methodology for adaptative planning of urban water systems under deep uncertainty

Araújo, Bruna Mattos; Pacheco, Gabriela Cristina Ribeiro; Fernandes, Camila Yarla; Lima, Diego da Silva; Alves, Conceição de Maria Albuquerque

doi:10.1590/2318-0331.282320220117

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Scientific/Technical Article • RBRH 28 • 2023 • https://doi.org/10.1590/2318-0331.282320220117 copy

A general methodology for adaptative planning of urban water systems under deep uncertainty

Planejamento adaptativo de sistemas hídricos urbanos no contexto de incertezas profundas: proposta metodológica

Authorship SCIMAGO INSTITUTIONS RANKINGS

ABSTRACT

Urban Water Systems (UWS) operate under a broad list of uncertainties. They usually depend on large amount of investments requiring long-term planning for a future full of changes with high degree of uncertainties (climate, social and economic). Many of these uncertainties do not have analytical representation neither they count on agreement among experts or decision makers concerning their influence in the performance of the UWS. The literature has named these changes as deep uncertainties (DU). This work presents a general approach to incorporate the influence of DU on planning and management processes of three types of UWS: 1) Water Supply Systems; 2) Drainage Systems and 3) Rainwater Harvesting Systems. The proposed framework defines steps toward the selection of the best policies and their evaluation in a broad set of scenarios. The particularities of each urban system led to adjustments in some steps of the general methodology. The approach proposed in this work was applied to a practical case, the Rainwater Harvesting Systems in the city of Ipameri, located in the State of Goiás, Brazil. The results highlight the impacts of DU factors on the system performance and reinforce this type of approach as a contribution towards adaptive planning for UWS.

Keywords:
Deep uncertainties; Adaptive planning; Urban water systems

Urban Water System	Objectives
Urban Water Supply System	- Maximization of reliability, calculated as the percentage of years when the water storage dropped below some percentage of its maximum capacity;
	- Minimization of restriction frequency, represented as the number of years when water restriction measures were applied;
	- Minimization of new Infrastructure Net Present Value (INPV);
	- Minimization of the cost of short term risk mitigation instruments;
	- Minimization of Worst First-Percentile (WFPC) of financial variability caused by drought management actions (restrictions and transfers) among all realizations.
Urban Drainage System	- Minimization of surface runoff volumes and peak flow;
	- Minimization of pollutant loads from the different types of land use;
	- Maximization of avoided costs;
	- Minimization of system costs (infrastructure and maintenance).
Urban Rainwater Harvesting System	- Maximization of the water demand served, taken as a percentage of non-potable demand;
	- Maximization of reliability, represented by the number of days that water demand is fully served;
	- Maximization of rainwater harvested, calculated as the percentage of the total rainwater volume collected that is actually used;
	- Maximization of Net Present Value of the URHS including a balance between costs and benefits (water tariff savings) of the system;
	- Maximization of Net Present Value per volume of consumed rainwater;
	- Maximization of Cost-Benefit Rate.

Application	Deep Uncertainty Factor
Urban Water Supply System	- New investment discount rate;
	- Water tariff;
	- Effectiveness of water consumption restriction;
	- Time to issue environmental licenses for infrastructure construction;
	- New infrastructure construction costs.
Urban Drainage System	- Stakeholder preferences;
	- Rate of land parceling and overall imperviousness;
	- Land use change;
	- Household use of Low Impact Development (LID) solutions (user cooperation);
	- Effectiveness of selected LID solutions;
	- New investment discount rate.
	- Rate of increase in operational and maintenance costs along the simulation.
Urban Rainwater Harvesting System	- New investment discount rate;
	- Water tariff;
	- Increase rate in operational and maintenance costs along the simulation;
	- Demand (potable or non-potable).

Application	Well-Characterized Uncertainties
Urban Water Supply System	- Evaporation rates in the reservoirs (water sources);
	- Streamflow (inflows) into the water sources;
	- Future water demand.
Urban Drainage System	- Historical rainfall data.
Urban Rainwater Harvesting System	- Historical rainfall data.

Application	Policies
Urban Water Supply System	- Short-term actions: water transfers, water consumption restriction, contingency water tariffs, educational campaigns towards rational water use. These are mostly drought mitigation actions.
Urban Water Supply System	- Long-term actions: new infrastructures or infrastructure expansion in the water system and network (reservoirs, pumping, water treatment plants).
Urban Drainage System	- Large scale: long-term planning of land use, LID solutions in public areas.
Urban Drainage System	- Small scale: individual LID solutions in household (land parcels).
Urban Rainwater Harvesting System	- Small scale: different configurations of the system in terms of water demand and rooftop area.

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[1] E-mails: bruna.mattos.araujo@gmail.com (BMA), gabrielacrpacheco@gmail.com (GCRP), camilayarla1@gmail.com (CYF), diego.lima@ifal.edu.br (DSL), cmaalves@gmail.com (CMAA)