Sefficiency (Sustainable Efficiency)
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There is a fundamental difference between descriptive and performance indicators of a water use system. The former responds to the question “What is happening?”, and the latter focuses on the questions, such as “Does it matter? Are we reaching targets?” To answer these questions, we use efficiency as a performance indicator, which “helps us attain more of the things we value.” To this end, we employ the theory presented in the previous Chapter to develop systemic, comprehensive and objective performance indicators based on a universal principle integrating the differentials of the three Pillars of water management, namely water quantity, water quality and water benefit. They reveal trade-offs among the three Pillars at three levels of management with climate and energy descriptors and stakeholder enablers. The internal behaviour and the trade-offs of these Sefficiency indicators are explained and shown graphically.
“Efficiency is thus not a goal in itself. It is not something we want for its own sake, but rather because it helps us attain more of the things we value” (Stone 2012).
“Resource efficiency means using the Earth’s limited resources in a sustainable manner while minimising impacts on the environment. It allows us to create more with less and to deliver greater value with less input” (European Commission 2019).
These two explanations of the concept of efficiency clearly establish its central significance, particularly under water scarcity. It also becomes clear that efficiency should promote sustainability and as will be seen in Chap. 5, it should be an integral part of equity. After understanding the concept, the key question is how to quantify it for a WUS based on the theory presented in this book. Sefficiency developed in this chapter fulfils this requirement and if followed properly produces sustainable solutions.
Sefficiency includes economic, environmental and social concerns in its formulation, which makes it a sustainable efficiency indicator for the management of a WUS. However, “sustainability is not a scientific concept, but rather a social goal. It implies an ethic. Public value judgments must be made about which demands and wants should be satisfied today and what changes should be made to ensure a legacy for the future. Different individuals have different points of view, and it is the combined wisdom of everyone’s opinions that will shape what society may consider sustainable” (Loucks 2002). This needs transparency and the involvement of all the stakeholders (see Sect. 3.2), because to become sustainable is complex. The quote also refers to “public value judgments”, which should be scientifically bounded (Sect. 1.2) as much as possible in order to produce solutions that are more robust for the integrated three Pillars. “In addressing the priority problem the task is that of reducing and not of eliminating entirely the reliance on intuitive judgments” (Rawls 1999). Even though our “priority problem” is different, but the statement also applies to Sefficiency, meaning that it reduces and constraints value judgments significantly.
Enables transparency through the fixed structure of the WUS
Enables stakeholders involvement for each WPI and its quality and benefit Pillars
Minimizes the risks of water scarcity
Adapts to uncertainty (e.g., climate change, population)
Lessens impact of severe conditions (e.g., drought)
Reduces new infrastructure
Supports economic growth
Improves cost effectiveness of water service
Allocates water better
Enhances conditions for recreation.
4.1 Proof of Sefficiency Indicators
In general, there exists both input and output efficiencies for any system (Coelli et al. 2005) in order to reveal the complexity of its structure and behaviour. Sefficiency equations compute the performance of a WUS from the supply and demand sides (FIW5c). The former is relative to inflow and the latter to consumption, which is a very important part of outflow (FIW2). This proof is based on Haie and Keller (Macro, Meso, and Micro-Efficiencies in Water Resources Management: A New Framework Using Water Balance 2012) and Haie (Sefficiency (Sustainable efficiency): a Systemic Framework for Advancing Water Security 2013). To start, let us be comprehensive and write the water balance in terms of these two perspectives.
Subscript ‘s’ stands for the useful part of all the WPTs and their corresponding WPIs within the curly brackets. This means that XS = WsX * X, with X being a WPI, XS its useful part, and WsX its Useful Criterion, which is presented in Eq. 2.1. For example, if X = ET, then its useful part is XS = ETS = WsET * ET.
iSE = Inflow Sefficiency (ic = 1): the ratio of useful Outflow to useful Inflow
cSE = Consumptive Sefficiency (ic = 0): the ratio of useful Consumption to Total Unrecoverable Flow (TUFS)
Generally, SE is multiplied by 100 to give a percentage, making it a positive number that has to be less than 100, meaning that the denominators must be greater than the corresponding numerators (if not, data may be inaccurate or unrealistic). It should be noted that Sefficiency rarely, if ever, is 100%, because it is very costly, even impossible, to have a WUS without undesirables (see Sect. 2.5).
A caution needs to be exercised as explained in Sect. 2.2 in applying weights to the sum or difference of the flows. For example, if ic = 0, the inside of the square brackets of Eq. (4.8) and Eq. (4.10) becomes C/ (I – R). However, Eq. 2.2 shows that I – R = C, hence making the inside of the brackets always equal to C/C = 1 and SE = s = 100%. Of course, this is not correct because, as was explained in the said subsection, first we have to apply the weights to each element inside the brackets and then make the arithmetic operations.
4.2 Levels of Management
- 2.Meso Sefficiency (MesoSE)
MesoSE ignores the main source of water.
The prefix meso means “Middle; intermediate” (Oxford Dictionary 2018). Usually, meso comes with micro and macro meaning something between these two.
MesoSE reflects the effect of a WUS on downstream by considering its returns.
- 3.Micro (MicroSE)
MicroSE does not consider the main source of water nor the returns of the WUS. This means that MicroSE ignores the effects on downstream with iMicro = cMicro.
Micro is about the flows or their proxies (e.g., Euros) of direct interest to the stakeholder (e.g., farmer, factory owner, ecosystem NGO, city planner).
It is not based on water balance and as a result prone to errors from the point of view of water management.
iMacroSE = Inflow MacroSES (ic = 1): the ratio of useful Macro-Outflow to useful Macro-Inflow
cMacroSE = Consumptive MacroSES (ic = 0): the ratio of useful Consumption to Macro-TUFs
iMesoSE = Inflow MesoSES (ic = 1): the ratio of useful Meso-Outflow to useful Meso-Inflow
cMesoSE = Consumptive MesoSES (ic = 0): the ratio of useful Consumption to Meso-TUFs
iMicroSE = cMicroSE = MicroSE: the ratio of useful Consumption to useful Micro-Inflow
Macro-Outflow = ET + NR + VD + RP
Meso-TUF = VA + OS + PP – (RF + RP)
Micro-Inflow = Meso-Inflow = VA + OS + PP
iMacroSEb (ic = 1): the ratio of beneficial Macro-Outflow to beneficial Macro-Inflow
cMacroSEb (ic = 0): the ratio of beneficial Consumption to Macro-TUFb
iMesoSEb (ic = 1): the ratio of beneficial Meso-Outflow to beneficial Meso-Inflow
cMesoSEb (ic = 0): the ratio of beneficial Consumption to Meso- TUFb
MicroSEb: the ratio of beneficial Consumption to beneficial Micro-Inflow
Equation (4.11) and Eq. (4.12) give eight important indicators, namely, iMacroSE, cMacroSE, iMesoSE, cMesoSE, iMacroSEb, cMacroSEb, iMesoSEb, cMesoSEb. They have 56 distinct combinations, but only 12 of them in three impact categories are important and will be covered in the following Sect. 4.4.2 (Three Impacts in Differentials of Sefficiency). The two Micro efficiencies are flawed as mentioned above in this subsection, with MicroSEb being analogous to the flawed Classical Efficiency explained in the Sect. 4.5 below.
Real cases are generally one to many and consequently have many WPIs. Here, two templates are available: (a) a free MS-Excel tool at Haie (Sefficiency (Sustainable efficiency) of Water-Energy-Food Entangled Systems 2016) as a supplementary document that has the equations and a simple format to simulate various cases side by side, (b) Appendix B: Sefficiency Template is the compact form used for this book. Although these are one to one templates (i.e., WPT → WPI), they can be edited to accommodate one to many scenarios.
Finally, in many applications, initially, the water managers can use Eq. (4.8) and Eq. (4.10). This reduces the needed water quantities to two, most of the time I and C, and utilizing the water balance equation, i.e., Equation 2.2, R can be found. These three water quantities need six weights for their quality and beneficial attributes to be able to calculate Sefficiency.
Most of the fields of science, if not all, employ weights explicitly and implicitly. They may be difficult or controversial to set but as the Nobel Laureate Amartya Sen (Inequality Reexamined 1992) affirms “weighting cannot really be, in any sense, an embarrassment” and “We cannot criticize the commodity-centred evaluation on the ground that different commodities are weighted differently.” Prices are weights and we readily accept that different commodities have different prices in the same location, and the same commodity has different prices in various locations.
In this book, there are two weights for each WPI (WbX and WqX), which are set according to the objectives of the WUS under analysis. They are explained in the next two subsections, along with a subsection on Usefulness Criterion.
4.3.1 Quality Attribute
“Most economic systems refer to pollution as an “externality;” a cost or benefit unaccounted for in the economic system. Pollution is a negative externality. Anyone taking rudimentary economics should know this. Solutions that have been working in the U.S. and many other places in the world involve government regulation of polluters. Take these externalized costs and integrate them into the system so that humans and aspects of nature that are suffering from their negative impacts without receiving the benefits are protected” (Fitch 2012).
Quality weight for treated water supplied to population is one (WqI = 1).
Quality weights of evapotranspiration (WqET) and some of non-reusable (WqNR), such as evaporation and bottled water are one.
The Water Framework Directive (European Parliament & Council 2000) introduced surface water status and groundwater status, which are general expressions of the status of a body of surface water or groundwater, respectively. Both include chemical status and classify waters into clearly defined categories with associated colours.
Canadian water quality guidelines for the protection of aquatic life employs Water Quality Index (CCME 2017), which has a calculator and a user’s manual.
The main global water quality index for domestic purposes is the Global Drinking Water Quality Index of the Global Environmental Monitoring System (GEMS) Water Programme, the United Nations Environment Program (UNEP 2007), and is based on the Canadian Water Quality Index.
Chinese Environmental Quality Standards with five classes are “formulated for implementing the Environmental Protection Law and Law of Water Pollution Prevention and Control of People’s Republic of China, and to control water pollution and to protect water resources” (MEEC 1997; MEEC 2018).
To calculate water footprint, Hoekstra et al. (The water footprint assessment manual: Setting the global standard 2011) introduced grey water footprint as “an indicator of freshwater pollution” in order to achieve a water quality objective/ standard. In this context, grey water footprint may be employed to set WqX under some conditions.
Food and Agriculture Organisation of the United Nations proposes the use of leaching fraction (Ayers and Westcot 1994) that is widely employed in irrigation management to avoid salt accumulation and can be used for setting quality weight (WqX = 1 − LFX, LF being leaching fraction).
4.3.2 Beneficial Attribute
The beneficial weight (WbX) is set by focussing on the nature and objectives of the WUS under consideration without considering its quality (WqX = 1). This is the usual way that the planning and management of the systems are carried out today, i.e., water quality of a system is dealt with separately according to its inflow needs and the downstream requirements. This weight should consider all the benefits that water brings to societies and natures: “Valuing water means recognizing and considering all the benefits provided by water that encompass economic, social and ecological dimensions. It takes many forms appropriate to local circumstances and cultures. Safeguarding the poor, the vulnerable and the environment is required in all instances” (UN-HLPW 2017). Hence, water benefits (interchangeable with water values according to this citation and others) are fundamentally linked to the objectives of a WUS, and include those that may not be quantifiable.
Public water supply to people has a WbI of one, meaning that all the water that enters into the water supply system (Inflow to a WUS) has the maximum benefit.
For irrigation systems, the so-called effective precipitation (Brouwer and Heibloem 1986) can be used to set the beneficial weight of precipitation (WbPP). This is doubly important for rainfed agriculture.
The non-beneficial ET is routinely estimated or calculated at least for irrigation systems.
Evaporation from lakes and reservoirs are calculated with a small fraction considered as beneficial.
4.3.3 Usefulness Criterion
These patterns seem significant particularly parsing the quality and beneficial weights in relation to Sefficiency and in the context of Benford’s Law. For example, the streamflow data so important to the water balance and hence the theory presented in this book should conform to the Benford’s Law and nonconformity could indicate specific issues with the data (Nigrini and Miller 2007). In other words, if the Usefulness Criterion in a locality diverges from the Benford’s law, it should raise a flag as to its accuracy, meaning that the beneficial and quality weights should be re-examined. However, the methodology to actually finding those divergences among many beneficial and quality weights is not clear. Nevertheless and beyond what was mentioned earlier in Sect. 2.2, these findings are indicative that the Useful Criterion defined in this book is sound and valid.
Trade-offs between the three Pillars of water management are inevitable particularly under water scarcity and are highly complex to quantify. Sefficiency as a centrepiece of the theory advanced in this book is about that complexity, meaning achieving a better trade-off and consequently reducing the undesirables. However, water resources development of an area has limits, i.e., the trade-offs of the three Pillars of water management have a reasonable upper bound (Sect. 1.2) in the context of the performance of systems. This feature can be used to reject the development plans, such as a new industrial plant, park or irrigated farm that reduce the performance of the system.
4.4.1 Jevons Paradox
Jevons Paradox is about those resources that have one state after usage and not two like water (FIW2a). Coal energy (the focus of Jevons Paradox of 1865) presents possible paradoxical trade-offs between supply side efficiency, demand (one state) and price. However, in water management, we have iSefficiency, water demand (two states), and price that reveal more complexity than energy efficiency, some of which are made clearer in the following points.
Various local and global drivers are increasing water scarcity meaning that effective supply is decreasing, which does not allow the price of water to decrease (actually the prices are increasing almost everywhere). These are not the underlying assumptions for Jevons Paradox.
Jevons Paradox does not consider pollution but Sefficiency does.
The solutions according to Sefficiency do not necessarily increase water demand or reduce its price because of the complex trade-offs of the three Pillars.
The use of technology in production processes of energy was another focus of Jevons Paradox. However, technology in Sefficiency is for data gathering in a learning process in order to better estimate the three Pillars, and make water balance (FIW1) more robust. In general, this increases the cost of water supply (not decreasing according to Jevons Paradox) but eventually makes planning and management of this vital resource more sustainable.
In the absence of proper policies, it is possible that production technologies, e.g., in irrigation, cause water consumption to increase. However, this does not mean that Sefficiency increases because of the trade-offs of the three pillars. In other words, it is not water consumption alone but rather the performance of the WUS within a specific situation that is the deciding factor. This is again different from the logical setting of Jevons Paradox.
4.4.2 Three Impacts in Differentials
- I/O impacts are due to the differences between inflow and consumptive Sefficiencies at the same Level and Pollution. This is done via the following four comparisons:
iMacroSE and cMacroSE
iMesoSE and cMesoSE
iMacroSEb and cMacroSEb
iMesoSEb and cMesoSEb
- Level impacts are due to the differences between Macro and Meso Sefficiencies at the same I/O and Pollution. This is done via the following four comparisons:
iMacroSE and iMesoSE
iMacroSEb and iMesoSEb
cMacroSE and cMesoSE
cMacroSEb and cMesoSEb
- Pollution impacts are due to the differences between full and beneficial Sefficiencies at the same I/O and Level. This is done via the following four comparisons:
iMacroSE and iMacroSEb
iMesoSE and iMesoSEb
cMacroSE and cMacroSEb
cMesoSE and cMesoSEb
Under a specific application, we should start with the worst impact difference and analyse it in more detail in conjunction with the trade-off patterns given in the next subsection. In general, these repeating reflections with stakeholders can progress to unconventional scenarios that sometimes can disrupt the usual functioning of a WUS. In other words, having water as the main priority, not the traditional ones, such as, economy, food, land, health or ecosystem, can lead us to innovative scenarios for the sustainable development of a region.
Equation (4.7) has more than 13 variables, which are WPIs and their weights. Changing one variable gives a different value for SE in a mostly non-linear fashion. Frequently, if one variable changes, others also vary making the combined effect of all the changes on SE more difficult to assess, meaning that trade-offs are much more complex. In general, the notion of trade-off in this subsection is to understand the behaviour and the structure of the domain (or space) of a policy or in this situation Eq. (4.7). Please see the end of Sect. 2.1 for the clarification of the notion of domain behaviour of an equation.
Horizontal axis shows C1, R1 or WR1
Vertical axis shows WC1 or WR1
Within these axes, contour lines of IN Sefficiency (iSE) or OUT Sefficiency (cSE) are drawn
Each figure shows various graphs along C1, R1, WC1 or WR1. We give four out of 20 graphs, which seems to be sufficient to portray the patterns and the trade-offs.
For example, Fig. 4.6 gives WR1-WC1-iSE graphs with WR1 and WC1 axes showing iSE contour lines for four fixed values of C1.
Because C1 + R1 = 1, specifying C1 or R1 will automatically fix the other, which produces equal graphs. For example, the graph for C1 = 0.3 in Fig. 4.6 is the same as the one for R1 = 0.7 of Fig. 4.7.
SE sometimes shows high variation or gradient. For example, in Fig. 4.9c, as cSE increases, the contours get closer to each other.
Various figures mirror each other. For example, Figs. 4.11 and 4.13 are mirrors of Figs. 4.10 and 4.12, respectively, giving equal SE for the complimentary C1 and R1 graphs. For example, iSE = 64%, for C1 = 0.8, WR1 = 0.4 in Fig. 4.10c, and R1 = 0.2 (= 1-C1), WR1 = 0.4 in Fig. 4.11c. For cSE = 60% and WR1 = 0.5, C1 = 0.75 in Fig. 4.12c, and R1 = 0.25 in Fig. 4.13c.
iSE decreases toward its minimum (zero) if WC1 and WR1 decrease toward zero (on the limit, iSE = WC1 = WR1 = 0). WC1 = 0 means totally useless Consumption or C1 = 0. WR1 = 0 means totally polluted Return or R1 = 0.
- iSE goes toward WC1 if C1 goes toward one, or WC1 and WR1 get closer to each other (on the limit, iSE = WC1 = WR1).
If in a real case WC1 is always greater than WR1, which seems to be a valid condition in most of the situations if not all, then the maximum that iSE can achieve is WC1.
If WC1 < WR1, then iSE > WC1; If WC1 > WR1, then iSE > WR1.
iSE goes toward WR1 if R1 goes toward one.
iSE goes toward C1 if WC1 goes toward one and WR1 goes toward zero.
cSE decreases toward its minimum (zero) as WC1 and/or C1 goes toward zero.
cSE increases toward its maximum (WC1) as WR1 and/or C1 goes toward one.
cSE and iSE go toward each other, if WR1 or R1 goes toward zero. In general, iSE and cSE go toward each other as they get closer to WC1 * C1, which at the limit, we have iSE = cSE = WC1 * C1.
There are alternative indicators that are also about computing efficiency, productivity, etc. One significant form is to specify the ratio of output to input. Output gives the things that we value, which goes along our objectives, and input is a sort of total. Here, we briefly discuss four alternatives, namely, Classical Efficiency (CE), Water Productivity (WaP), Effective Efficiency (EE), and also Resiliency (RE).
4.5.1 Classical Efficiency
Numerator (beneficial water): beneficial water use, consumption or required
Denominator (total water): total water applied, abstracted, allocated or required
Incompleteness of water flows, particularly the lack of the inclusion of returns in the equation, which also makes it inadequate for any multi-objective WUS.
CE does not obey water balance, one of the most important laws in studying and designing water systems.
Partial consideration of Usefulness Criterion, i.e., lack of a comprehensive concern for applying water quality and benefits. For example, the numerator considers the beneficial part, but this distinction is not extended to the denominator. Furthermore, CE is a quantity indicator, with little or no consideration for water quality.
Many experts state that increasing CE by decreasing the total water (denominator) saves water for downstream. However, in most cases such a water saving is actually negligible and close to zero. Please see a common example about this myth in Chap. 6. For now, let us focus on the application of CE in agriculture and urban areas.
In irrigated agriculture, CE is mostly defined as CE = ETb/VA (Seckler et al. 2003), meaning the ratio of beneficial ET to water applied. Various other names are given to CE, such as, irrigation efficiency and water use efficiency. As just mentioned CE is flawed and many authors, including Willardson, et al. (1994) and Haie and Keller (2012) have discussed its problems. Additionally, various authors have defined CE with some variations but all are flawed. For example, efficiency is shown as 1/CE and given a different name, or leaching fraction is applied to VA (see Sect. 1.3), or PPb (also called effective precipitation) is subtracted from ETb, or change in storage is subtracted from VA (in practice never used, e.g., Burt et al. (1997)), etc. In reality, CE is a fraction, which conveys very little information (Willardson et al. 1994) and not a scientific and logical performance indicator. However, CE is, to some extent, legitimate from the perspective of the crop but not water, meaning that for agronomists, CE may advance some information but for water managers, it is not suitable at all. These two perspectives create confusion in the mind of many experts, making it another example of why this book insists on the centrality of water in managing it.
In urban areas, the concept of CE, i.e., Eq. (4.16), is also wide spread and equally flawed due to the three issues mentioned above. Let us see three examples by focusing on concepts (index 1 = before intervention, and index 2 = after intervention for CE improvement):
Xb1 = Xb2 with VA2 < VA1 (this is the 1st part of the CDWR definition of urban efficiency)
Xb1 < Xb2 with VA2 = VA1 (this is the 2nd part of the definition, which is after “or”)
A third possibility is not presented in the above CDWR definition of urban efficiency with Xb1 ≠ Xb2 and VA2 ≠ VA1. Under these conditions, CE improves if Xb1 * VA2 < Xb2 * VA1.
“A study from 2007 on the water saving potential in Europe, estimates that water efficiency could be improved by nearly 40%”. This study (Dworak 2007) was funded by the European Commission, Directorate-General Environment and produced a report that goes into many sectors and services. Its overall outlook defines water saving potential stating that it “can be achieved by improving the efficiency of various uses of water without decreasing services or by cutting back the use of a resource, even if that means cutting back the goods and services produced by using that resource.” This definition gives two possibilities, which Eq. (4.16) should be used for their understanding: (i) CE2 > CE1 and Xb2 ≥ Xb1, (ii) after “or”, VA2 < VA1 and X2b ≤ Xb1 with an implicit assumption that CE2 ≥ CE1.
“The study identifies the need for an EU approach that could contribute to water efficiency across Europe, regardless of the variation in climate, population or land use practices in Member States.” This study on water efficiency standards (Benito 2009) was funded by the European Commission, Directorate-General Environment and produced a report that focusses on urban (buildings and industries) and agriculture. This report defines water efficiency as “the relationship between the amount of water required for a particular purpose and the amount of water used or delivered”, which is a CE type concept.
Third, the Portuguese Water Use Efficiency Plan - PNUEA (National Laboratory of Civil Engineering 2001) is used in many activities related to water, such as, River Basin Management Plans (Portuguese Environment Agency 2019b), and Strategic Environmental Assessment of the Roadmap for Carbon Neutrality 2050 (Portuguese Environment Agency 2019a). PNUEA is defined for various types of water users, such as, urban, agriculture and industry. In its indicator section, it defines water use efficiency as the ratio of “useful consumption” to “effective demand”, and sets water loss (%) equal to (100 – efficiency). This CE type equation does not explain the meaning of the words useful, consumption and effective. In practice, PNUEA uses Eq. (4.16) and defines various efficiency and investment targets that have been adopted by the decision-makers.
Finally, there are those who only use water quantity to calculate the performance of a system in the form of (water quantity/ total water quantity), which obviously is wrong. Section 6.2 gives an example with more explanation.
4.5.2 Water Productivity
‘production’ can be yield (kg), mass of production (kg), monetary value (€), amount of product—different from water (m3), etc.
‘water quantity’ can be water applied (VA in m3), evapotranspiration (ET in mm), etc.
WaP as a ratio of output to input is similar to CE and equally a flawed indicator for water management due to the issues given for CE, and various other reasons given by some experts and organisations (Wichelns 2014; FAO & WWC 2015). There are also variations to Eq. (4.17), such as 1/WaP and all are flawed. For example, Coca Cola Company uses it under the name Water Efficiency meaning amount of water used (litre) per amount of product made (litre) (Coca-Cola Company 2018). In general, production depends on many inputs including water in a nonlinear fashion, and as an input becomes scarcer, production becomes more dependent on that scarce input. Under what combination of inputs, the productivity of the system (i.e., all input considered) is good-enough? The answer to this question erroneously narrows down to one (not many) input depending on the expert. For example, under the same conditions for an irrigated agriculture, the answer of the water experts is proper amount of water; the answer of the soil experts is better soil; the answer of the pest experts is better pest control; the answer of the economic experts is about market or land ownership, etc. Anyhow, Eq. (4.17) may prove to be valuable for agronomists and particular industries but not for water managers who should aim for a comprehensive and good-enough performance of a WUS.
4.5.3 Effective Efficiency
EE is more complete than CE and meaningfully advanced the concept of water efficiency. However, it was not developed in a systemic and comprehensive manner and consequently is an incomplete formulation and gives inaccurate results. Subtracting PP (inflow) from ET (outflow) is not correct from the water perspective (and cannot be applied to rain fed agriculture). There is no accounting for RP, which can be of great importance, e.g., for groundwater. In addition, it does not include NR (a significant flow in some applications) because EE is for irrigated lands only. On the other hand, it does not comprehensively consider the Usefulness Criterion, i.e., water quality and benefits. For example, the beneficial part of ET is in EE, but this distinction is not extended to V1 and V2; and for quality, it only considers salt, i.e., WqX = 1 – LFX (Sect. 1.3). Finally, although its name consists of the word “effective” but it was not defined, and as such, along the paper, it gets diverse meanings as applied to different things, such as effective inflow, effective precipitation, and effective efficiency.
Having in mind the definition of ‘satisfactory’ given in Sect. 2.4, Loucks and Van Beek (Water Resources Systems Planning and Management: An Introduction to Methods, Models and Applications 2005) define resilience as given in Eq. (4.19) stating that “Resilience can be expressed as the probability that if a system is in an unsatisfactory state, the next state will be satisfactory. It is the probability of having a satisfactory value in time period t + 1, given an unsatisfactory value in any time period t.” Hence, resilience is an indicator of the response of the system, i.e., the speed of the recovery from an unsatisfactory condition (CDWR 2019). For example, a young person is more resilient than an old one, because she can recover faster from a sick (unsatisfactory) condition, such as a flu or Covid-19. In evaluating and improving resiliency, a system, such as a water network, has many resilience metrics that can be used depending on the scenario of interest. For an example in water networks, please refer to the WNTR software of U.S. Environmental Protection Agency (Klise 2017).
No system is absolutely sustainable or resilient, meaning that there are degrees to sustainability and resiliency. For example, a resilient system may respond well to a 50-year flood, but fails to recover under more sever ones.
Any sustainable system must be resilient to foreseeable disruptions. Again, this is not absolute and it is possible to imagine sustainable systems that fail to a particular level of a specific disaster. No system can be highly resilient to all types of disruptions with all levels of intensity and extent.
The relativity of these concepts does not mean that all systems are adequate. On the contrary, a sustainable and resilient system should be continually enhanced through learning (FIW5b; Sect. 3.2) in the context of improving Sefficiency in Sequity.
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