Integrated Modeling Concept

Integrated water resources management (IWRM) is a multidisciplinary approach to managing water. There is a long history to the many foundations of this ideology.This concept was first introduced in 1977 at the United Nations Global Water Conference in Mar de Plata (Biswas, 2004).

Although IWRM was not fully realized at that time, it addressed issues of sustainable water management. In 1992 these issues were revisited, both at the International Conference on Water the Environment (ICWE, 1992) in Dublin, Ireland, and the World Summit on Sustainable Development in Rio de Jeneiro (WSSD). From the ICWE came the Four Dublin Principles, defining water both as a human right and as an economic good. These principles can be stated succinctly as: (1) fresh water is finite, needed for life, development, and environment; (2) developing and managing resources involves participation of all users; (3) women have a central role; and (4) water must be valued economically. The Agenda 21 (UN, 1992) that came from the WSSD complimented the Dublin Principles by investigating the social and economic dimensions of water. The Agenda 21 outlined an action plan for sustainable development, developed by

18

multiple organizations at the Rio de Janeiro conference. Some of the discussed topics that relate to IWRM are: (1) decision making through integrating development and the economy (Agenda 21, Section 1), and (2) the application of integrated approaches to protect and manage fresh water supplies (Agenda 21,Section 2). Both the Dublin Principles and the Agenda 21 built the foundations of IWRM, through considering management in a way that integrates multiple groups.

From these fragments came many different interpretations of IWRM.

This paradigm shift towards IWRM has seen increasing trends to incorporate socio-economic and ecological dimensions in water management (Pahl-Wostl, 2011). In particular these socio-economic considerations were addressed by key IWA UNEP (2002) principles: recognition of water as an economic good, integrating water and environmental management, and recommendation of a systems approach. Further, this shift recognized the need to incorporate uncertainty, multiple sectors and the science of integration of parts (Lansey et al., 1989; Cai et al., 2003; Letcher et al., 2004). The common adage “the whole is greater than the sum of its parts” is well applied to complex water resource systems, and solutions should consider the integration and not just the parts.

There are several requirements identified for an IWRM model to be successful at providing useful information to the modeler: (1) The need to link spatial and temporal scales suitably (Maneta et al., 2009)); (2) modeling of conjunctive water sources, such as ground and surface water (Fernandez and Selma, 2004; Schoups et al., 2006; Pulido-Velazquez et al., 2008); (3) linking supply with demand forecasting (Hanson et al., 2012); (4) accounting for feedbacks within a system (Fernandez and Selma, 2004; Chen et al., 2005) and (5) providing a social and/or economic valuation (Heinz et al., 2007; Ward, 2009). Concerns for these five requirements pointed to the need to integrate water, economy, and environment utilizing a systems approach. A

hydro-19

economic model is a relatively simple form of IWRM modeling, as it considers just the hydrological and economic aspects, but can be extended to include environmental aspects.

“Combining engineering, economics and hydrological science, a hydroeconomic approach is well positioned to help foster integrated water resources management.”(Harou et al., 2005)

Two broad approaches to hydro-economic modelling developed were the simulation and optimization approaches. Both of these approaches were seen to have advantages and disadvantages as described by Harou et al. (2005). Simulation has the advantage of being conceptually simpler than optimization, and allows one to examine changes to a pre-defined scenario. The main disadvantage of simulation models is that they do not provide a means to determine a best solution. Conversely, optimization models allow one to identify a best solution based on one or more pre-defined objective functions, e.g. minimizing cost or maximizing marginal utility. Optimization models are often more complex than simulation models and do not normally provide any means to understand the system. Further, Keeney and Wood (1977) argued against optimization models on the grounds that the objectives when optimized may not be meaningful to stakeholders.

Brouwer and Hofkes (2008) segregated hydro-economic models into three basic groups:

modular, integrated/holistic, and metamodel. A modular approach consists of components and sub-models that interact with each other as exogenous forcing. This allows for multiple modeling platforms to be combined, and coordinated. The integrated/holistic approach treats all components as one model, allowing equations to be solved endogenously, as seen in a systems approach. Less common are the meta-models, which relate one model to another through cause and effect.

Although there is a multitude of ways to classify integrated water resources models, the distinctions by Brouwer and Hofkes (2008) are succinct. In short it is convenient to consider two

20

modeling approaches; optimization-based and simulation-based modeling, each with three model structures.

The application of integrated water resource systems models is the theme of the following sections. It was shown as a means to translate IWRM principles to practice. An integrated model should consider scale, conjunctive water use, supply and demand, and feedbacks and the economy- although not all considerations are always present (e.g. a surface water dominant system may have little feedback with groundwater sources). This can be achieved through coupled and holistic models, both optimization- and simulation-based. From the previous paragraphs one could appreciate the breadth of applications and multitude of factors involved. Depending on the case study, one has a variety of options to choose from. The remainder of this review will discuss the application of both optimization- and simulation-based IWRM models, as well their use as emulators.