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CIVL2010 Environmental Engineering Assignment
Project: “Tragedy of the Commons” I. INTRODUCTION The overall goal of the project is to develop a better understanding of environmental sustainability by focussing on a specific type of sustainability problems, namely the ‘Tragedy of the Commons’ (TotC). TotC refers to situations in which profit-seeking, self-interest leads to the (sometimes irreversible) depletion of a renewable natural resource. It is a classical environmental sustainability problem that occurs widely (e.g., Ocean fisheries, grazing, forest logging, air pollution, overuse of groundwater for irrigation). Unless the use of such commons is tightly regulated, through rules, laws or social customs, the resource in question runs a high risk of collapsing. This is because individuals pursuing rational self-interest will be tempted to boost profit by increasing means of production (more forest logging equipment, more fishing vessels, more efficient fishing technologies such as GIS-based location of prey, more wells for groundwater extraction etc.) 1. The questions of interest to resource managers are: a) what is the level of exploitation below which collapse can be avoided and b) what structural features may be introduced into the system to keep it sustainable? For a non-technical 6-min introduction to TotC, check this video The project’s aims are to: 1. understand key features and risks in TotC systems. 2. identify ways in which resources under TotC can be managed sustainably. 3. critically appraise System Dynamics as a tool for addressing sustainability. II. MODEL Overall Description Figure 1 shows a VENSIM system dynamics model2 describing the dynamics of interaction between three stock variables: • renewable resource (s1) in t (tonnes) • production capital (s2) in $ and • accumulated net profit (s3) in $ Exploitation of the resource (consumption) is offset by its regeneration. Regeneration is assumed to be governed by a logistic growth equation, subject to an erosion floor limit. Exploitation depends on a) production capital (i.e., cumulative capital set aside for the investment needed for exploiting the resource) and b) a production goal. Yearly production capital (i.e., net investment) is a fraction of net profit. 1 p. 184 of Hartmut Bossel’s System Zoo 2 Simulation Models – Climate, Ecosystems, Resources. 2007, Books on Demand GmbH, Nordestet, Germany. 2 Ibid. 2 Figure 1. Simplified System Dynamics Model of the Tragedy of the Commons (adapted from Bossel, 2007, model Z417) Key Dynamics A summary of key dynamics follows (see appendix for more detailed description): • Renewable resource (s1) is accumulated regeneration f1 minus accumulated consumption f2: o Regeneration (resource growth) f1: logistic growth subject to erosion floor limit (c3) (if s1 drops below c3, resource can no longer grow, and regeneration rate is set to zero). The two parameters of logistic growth are regeneration rate c4 and maximum capacity c5. o Consumption (resource exploitation) f2: proportional to production capital (s2) and resource (s1): f2=c7s1s2 (where c7 is specific production rate) • Production capital (s2) is accumulated net investment f3: o Net investment (f3) is determined by 2 factors at any point in time: ▪ Annual net profit f4 whereby a constant portion of f4 is re-invested in production, adjusted for goal discrepancy (see next bullet point) ▪ Goal discrepancy v3, i.e., how far is the system from a set production goal – the further from the goal, the more investment; hence, v3 is calculated as 1-v2/c9 (0≤v3≤1) where v2 is annual production and c9 is production goal; v2 is proportional to s1 and s2 (v2=c7*s1*s2 where c7 is specific production rate). ▪ In summary: f3 = c10*v3*f4 • Accumulated net profit (s3) is accumulated annual net profit f4: o Annual net profit (f4) is annual revenue v4 minus annual operating cost v5; v4 is the product of resource price c8 by annual production v2; v5 is product of specific operating cost by production capital s2. 3 III. PROJECT WORK ON PROJECT DAY On project day, you will work within a group of 4 students, either face-to-face or in zoom rooms. If you are taking the face-to-face option of the UoS, make sure to bring a laptop to class. Also, knowledge of system dynamics and some experience with VENSIM are pre-requisites for the project. Make sure you read the lecture notes and do the relevant tutorial exercises BEFORE project day. 1. In the UoS Canvas website, go to Modules → Sustainable Systems → download totc1 and open it with Vensim. This is the VENSIM version of the model discussed above and shown in Figure 1. In this project, a sustainable regime3 is defined as one which, within the timeframe of the simulations (0-200 years), reaches an equilibrium characterised by the following: a) renewable resource s1 ≥ 10% of maximum capacity c5, and b) accumulated net profit s3 ≥ $0.5 Note that conditions a) and b) need only be achieved at equilibrium (up to 200 years of simulation time). 2. Conduct the following tasks with your fellow group members: a. Develop a sustainable regime WITHOUT changing existing structure as follows (35%): i. Examine the model visually: identify at least 3 key feedback loops in the system (i.e., links that go, directly or indirectly, from stocks to inflows or outflows), and briefly discuss their implications. (½ page maximum). (10%) ii. Run the model using initial data provided in the model (call this scenario “base case”): is the current regime sustainable? What led you to this conclusion? (graphs: ½ page; text: ½ page maximum). (2.5%) iii. Without doing any other simulation or calculation, fill out table 1 based on your reading of the structure in Figure 1 and your “hunch” (in this question, you do NOT get marked down for providing the wrong answer) and add it to your report (2.5% just for filling the table): Table 1 If a parameter (c1-c10) increases, the stock variable (s1-s3): increases (+), decreases (-), increases and decreases at different times (u), has no effect (0) or cannot tell (?). Write one of the 5 symbols (+,-,?,u,0) in each cell: s1 s2 s3 c1 c2 c3 c4 c5 c6 c7 c8 c9 c10 3 The word “regime” is used to indicate the behaviour of a structure under a given set of input parameters. In other words, the same structure may behave very differently under different regimes. Hence, a new regime can be obtained by a) changing the parameters of a structure without changing the structure itself, b) changing the structure (removing or adding variables or feedback links) but not the parameters or c) both. 4 iv. Run the SyntheSim capability and use the provided sliders to assess sensitivity to input parameters c1 to c10 (call it “sustainable 1”). Make sure you assess one parameter at a time (by resetting before you move to the next parameter). How does it compare to your guess in 2.a.iii? In your report, include the following: a) Another version of table 1 but this time filled based on your SyntheSim observations; b) choose 1 parameter whose effect was contrary to your guess and discuss it (what was the logic behind your guess and what was the actual effect and why). (table + ½ page maximum) (10%) v. Based on the 2.a.iv, reset model, exit SyntheSim, choose ONE or TWO input parameters and change them so as to transform the regime into a sustainable one (still under scenario “sustainable 1”). In your response: a) include a screenshot of the graphs, b) describe how your solution works (drawing on a real-life example of your choice such as forest logging or groundwater abstraction) and c) identify, from your results, how far in the future will resource exploitation stop being profitable (if at all). (½ page response + ½ page graphs) (10%) b. Develop a new sustainable structure as follows (35%): i. Based on the analyses in 2.a, identify one or more pathologies causing unsustainable behaviour (e.g., is there a missing feedback loop or connection between the stocks-constants- inflows/outflows?) (½ page maximum) (5%) ii. Change the structure to create a sustainable regime. Feel free, if needed, to change the values of the parameters and/or to create new parameters. However, keep the change minimal and avoid creating new stocks. Make a copy of totc1, call it totc2, open it, implement the solution you propose (“sustainable 2”) and test it. (1½ page maximum, including model structure, description, graphs…). (25%) iii. What are the advantages/drawbacks of the solution developed in 2.b.ii compared to the one in 2.a.v? (½ page maximum). (5%) 3. Based on this exercise and on what you’ve learnt in the classroom, can greenhouse gas emissions be analysed as a Tragedy of the Commons and why (e.g., does the problem satisfy TotC conditions? What would be the stocks in question etc.)? (½ page maximum). (15%) 5 4. Critically appraise System Dynamics as an approach to Sustainability. Specifically, based on parts 2 and 3 above, discuss the strengths and limitations of System Dynamics as a framework for policy and decision- making on environmental sustainability. In responding, you may wish to consider one or more of the following questions: a) How reductive are the models, i.e., are there important elements of reality that they fail to consider? b) How useful are the models for real-life situations and what are their drawbacks? c) Do the models have inherent biases and, if so, to whom? (½ page maximum). (15%) For questions 3 and 4, you are encouraged to search the literature and read external documents, including resources in the list of readings for the UoS (especially under the section on Tragedy of the Commons). IV. OUTPUT Submit your assignment on Canvas (1 submission per group) including: a) a report with i. a cover page showing group number and SIDs of group members (but not their names so as to ensure marking anonymity); ii. main body with answers to questions in sections 2 to 4; the report, excluding cover page, should not exceed 8 pages (New Times Roman size 11, single space paragraphs, 2.54cm margins on all 4 sides) - reports in excess of this limit will NOT be marked. and b) files totc1.mdl, totc2.mdl, base case.vdx, sustainable 1.vdx, sustainable 2.vdx. V. APPENDIX: DETAILED TECHNICAL DATA AND EQUATIONS OF ORIGINAL MODEL • Main settings: o Time unit: [year] o Resource unit: [t] (for ton) o Monetary unit: [$] o Interval: 0 to 200 year o Time step: 0.05 year • Initialisation Parameters: o Initial resources c1 [t]: c1 = 1 o Initial production capital c2 [$]: c2 = 0.01 • Stock variable 1: renewable resource s1 [t] (initialised at c1) o Constant Parameters: ▪ erosion limit c3 [t]: c3 = 0.05 ▪ normal resource regeneration rate c4 [ t t.year ]: c4 = 0.1 6 ▪ max capacity of resource c5 [t]: c5 = 1 o Variables: ▪ actual regeneration rate v1 [ t t.year ]: v1 = { 0 if s1 < c3 c4 if s1 ≥ c3 o Flows: ▪ inflow: regeneration (logistic growth) f1 [ t year ]: f1 = v1s1 (1 − s1 c5 ) ▪ outflow: consumption f2 [ t year ]: f2 = v2 o Stock variable: s1 = c1 + ∫ (f1 − f2)dt t 0 • Stock variable 2: production capital s2 [$] (initialised at c2) o Constant Parameters: ▪ specific operating cost c6 [ $ $.year ]: c6 = 0.1 ▪ specific production rate c7 [ t t.$.year ]: c7 = 1 ▪ resource price c8 [ $ t ]: c8 = 1 ▪ production goal c9 [ t year ]: c9 = 1 ▪ investment rate c10[1]: c10 = 0.1 o Variables: ▪ annual production v2 [ t year ]: v2 = c7s1s2 ▪ goal discrepancy v3[1]: v3 = 1 − v2 c9 ▪ revenue v4 [ $ year ]: v4 = c8v2 ▪ operating cost v5 [ $ year ]: v5 = c6s2 o Flows: ▪ inflow: net investment f3 [ $ year ]: f3 = c10v3f4 o Stock variable: s2 = c2 + ∫ f3dt t 0 • Stock variable 3: accumulated net profit s3 [$] (initialised at 0) o Flows: ▪ inflow: annual net profit f4 [ $ year ]: f4 = v4 − v5 o Stock variable: s3 = ∫ f4dt t 0
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