Strategic decision making under climate change: a case study on Lake Maggiore water system

Transcription

1 doi: /piah Eoling Water Reource Sytem: Undertanding, Predicting and Managing Water Society Interaction Proceeding of ICWRS2014, Bologna, Italy, June 2014 (IAHS Publ. 364, 2014). Strategic deciion making under climate change: a cae tudy on Lake Maggiore water ytem M. MICOTTI 1, R. SONCINI SESSA 1 & E. WEBER 2 1 Dept. Electronic, Information and Bioengineering, Politecnico di Milano, Italy micotti@elet.polimi.it 2 Fondazione Politecnico di Milano, Italy Abtract Water reource planning procee inole different kind of deciion that are generally ealuated under a tationary climate cenario aumption. In general, the poible combination of interention are mutually compared a ingle alternatie. Howeer, the ongoing climate change require u to reconider thi approach. Indeed, what hae to be compared are not indiidual alternatie, but familie of alternatie, characterized by the ame tructural deciion, i.e. by action that hae long-term effect and entail irreocable change in the ytem. The rationale i that the tructural action, once they hae been implemented, cannot be eaily modified, while the management deciion can be adapted to the eoling condition. Thi paper conider thi methodological problem in a real cae tudy, in which a trategic deciion ha to be taken: a new barrage wa propoed to regulate Lake Maggiore outflow, but, alternatiely, either the preent barrage can be maintained with it preent regulation norm or with a new one. The problem wa dealt with by multi-criteria deciion analyi inoling many takeholder and two deciion-maker. An exhautie et of indicator wa defined in the participatory proce, conducted under the integrated water reource management paradigm, and many efficient (in Pareto ene) regulation policie were identified. The paper explore different formulation of a global index to ealuate and compare the effectiene of the clae of alternatie under both tationary and changing hydrological cenario in order to ae their adaptability to the ongoing climate change. Key word deciion making; climate change; multi-criteria analyi; reeroir planning and management INTRODUCTION The many different action conidered in water reource planning differ in timing, cot, impact and complexity. Uually thee action are ealuated under a tationary climate cenario in which all the poible combination of action are mutually compared a ingle alternatie. Howeer, the ongoing climate change require u to re-conider thi paradigm ince tructural deciion hae longterm effect and entail irreocable change in the ytem, while management deciion can be progreiely adapted to eoling climate and ocial condition. Therefore in trategic deciion making it appear more ueful to not compare indiidual alternatie, but clae of alternatie that are characterized by the ame mix of tructural action. The claical Multi Attribute Value Theory (MAVT, Keeney and Raiffa 1976) i well uited for comparing indiidual alternatie, but it i not equipped to deal with trategic deciion in the ene mentioned aboe, i.e. for comparing clae of alternatie. In the author knowledge, the literature ha not yet offered any olution oling it. In thi paper we propoe to tackle the problem till remaining in the conceptual frame of MAVT, by aociating each alternatie with a uitable global alue and then to compare the clae on the bai of the population of thoe alue. In order to introduce the problem we preent in the next ection a planning tudy on Lake Maggiore in a climate change propectie. In the third ection a method for comparing clae of alternatie i preented and it ignificance i ealuated in the fourth one by applying it to the Lake Maggiore cae. Concluding remark cloe the paper. THE LAKE MAGGIORE CASE-STUDY Lake Maggiore (locally named Verbano) i a cro-border lake, hared between Italy and Switzerland, et among the pectacular peak of the Central Alp. We conider it water ytem a compoed of the lake itelf, it catchment and the Rier Ticino that flow out of the lake. The lake i regulated by a barrage, the Miorina barrage, which i managed on the bai of an international agreement, igned between Italy and Switzerland in The agreement tate that the outflow from the lake may be regulated only when the lake leel (meaured at Seto Calende hydrometer) i within a uitable, time- Copyright 2014 IAHS Pre

2 Strategic deciion making under climate change: a cae tudy on Lake Maggiore water ytem 533 arying regulation range ([ 0.5 m, 1 m] on Seto hydrometer from March to October, and [ 0.5 m, 1.5 m] in the ret of the year). Outide of thi range the lake outflow mut be et to pecified alue. Namely, when the lake leel equal the minimum of the regulation range, the outflow mut be et equal to the lake inflow, in order to preent further dropping of the leel; while, when the leel equal or exceed the maximum of the regulation range, the outflow mut be the larget feaible one, i.e. the barrage gate hould be completely open, in order to minimize the flood peak on the lake. The planning tudy we dealt with concern the ealuation of the opportunity of ubtituting the Miorina barrage with a new one and/or the identification of a new regulation policy. More preciely we conider the following clae of alternatie: Cla A: The Miorina barrage remain unchanged, a well a the regulation range; the daily releae i defined by a regulation policy, when the lake leel i within the regulation range; when it i outide of it the preent contraint remain alid. Cla B: A cla A, but for the regulation range that i aumed time inariant and equal to [ 0.5 m, 1.5 m]. Cla C: The Miorina barrage i ubtituted by the new barrage propoed by AIPO (Agenzia Interregionale fiume PO) and a tretch of the Rier Ticino i dredged (Da Deppo and Salandin 2006); the regulation range ha no upper limit and thu the new regulation policy ha to be defined for all poible lake leel. A can be een in Fig. 1 thee tructural interention will ignificantly enlarge the regulation poibilitie and, conequently, the releance of the regulation policy. Fig. 1 Stage dicharge relationhip for Lake Maggiore: black line are related to the preent barrage, the grey one to the new barrage; the continuou line concern the minimum releae, the dahed one the maximum. The filled area i the preent regulation pace, the way area the future one. A model of each component of the ytem wa identified and implemented in the TwoLe uite (Soncini-Sea et al. 2003), a DSS to deign regulation policie uing the Dynamic Programming algorithm (Bellman 1957). More than 1300 Pareto-efficient alternatie were identified within the three clae, focuing the inetigation in the more promiing compromie area. The participatory approach The identification of the criteria hierarchy conidered in the planning tudy wa carried out together with the takeholder, who were inoled in the negotiation later on, following an integrated approach to participation (Reed 2008). The hierarchy reflect the complexity of the ytem: a et of 120 indicator ha been identified and clutered into 20 different ector, repreenting interet and takeholder playing in the ytem (e.g. the indicator Maximum flooded area oer the time horizon for Lake Flood ector or the indicator Aerage ditance from natural hydrologic regime for Rier Enironment ector). The effect induced by each one of 1300 Pareto efficient alternatie were therefore meaured by a ector of 20 alue, one for each ector, computed with uitable alue function on the bai of the indicator outcome.

3 534 M. Micotti et al. The ealuation of the indicator wa baed on a tationary hydrological cenario, more pecifically on the time erie of the hitorically regitered inflow, in order to gie takeholder the poibility of comparing the performance of the alternatie with repect to the effect of the hitorical regulation, of which they hae a memory. Since the clae of alternatie include the poibility of a tructural modification, which will hae long-term effect, the ealuation on the tationary cenario i inufficient due to poible climate change. Hydrologic cenario under climate change were therefore generated (the generation i due to R. Bordoy and P. Burlando, Zurich ETH), inoling downcaling time erie produced by the regional model REG-CM3 (Pal et al.; 2007), fed by global cenario generated by model A1b (IPCC 2007). Ten equiprobable rainfall and temperature time erie for the control period and ten for the decade were thu obtained. Thee cenario were then routed through the patially ditributed rainfall runoff model FEST-WB (Raazzani et al. 2008), to obtain the correponding hydrologic cenario, which were ued to imulate the performance of the ytem under the 1300 alternatie. The indicator o obtained were ued to ae the ratio of ariation between the ector alue ealuated on the decade and the one ealuated on the correponding control cenario. Thee ratio were finally ued to project the ector alue etimated with the preent tationary cenario to the decade ; in o doing the bia that i preent in the climate model, and therefore in the ector alue ealuated with their output, wa remoed. A METHOD FOR COMPARING CLASSES OF ALTERNATIVES The information produced with a planning proce baed on claical MAVT can feed negotiation round, at the end of which, one (or a retricted number of) appealing compromie alternatie() i (are) identified. When the future cenario i perceied a tationary, thi choice i well baed. In contrat, in the preence of an ongoing climate change the goal i not to identify the bet compromie alternatie among the many efficient one, but to elect one cla of alternatie, ince, a mentioned in the introduction, the tructural action will affect the ytem in the long run, but the management policy can be ubject to reiion. Therefore the choice of one cla cannot rely on a pecific regulation policy, i.e. on one pecific alternatie, but it mut conider all of them in ome uitable ene. Our propoal i to compare clae of action with a procedure in two tep: by firt defining a global alue function in order to aociate a global alue to each alternatie (a in MAVT) and then comparing the clae on the bai of the population of the global alue they produce. Formulation of the global alue function The idea i claical: to aociate a global alue V j.a to the jth alternatie of cla A by aggregating it ector alue VV jj.aa for all the ector. MAVT ugget conideration of their weighted um, but a well-defined way of etting thee weight doe not exit when a compromie alternatie doe not hae to be elected, a in our cae. The formulation we propoed are baed on the aumption that no compenation i poible either among the ector (Formulation 1) or among group of ector (Formulation 2). In that cae it wa proed (Keeney and Raiffa 1976, Triantaphyllou and Baig 2005) that a uitable form of the global alue function i the (eentually weighted) product of the ector alue. Then, auming all weight equal to 1, our firt propoal i the following: Formulation 1: V 1 = S 0 where 0 i the th ector alue for the reference alternatie A0 and S i the ector et. Formulation 1 implie that when an alternatie, ay the jth alternatie of cla A, completely diatifie ector, i.e. when 1 j, A = 0 for ome, then V = 0. In other word, each ector ha a eto power. Accordingly an alternatie with a high global alue will likely be a trong one. (1)

4 Strategic deciion making under climate change: a cae tudy on Lake Maggiore water ytem 535 The econd formulation i baed on the aumption that the ector et S can be partitioned into G group, among which compenation i meaningful, while compenation i alid within each group: Formulation 2: G 2 1 V = (2) N g= 1 g N g 0 where N g denote the cardinality of the group N g of ector. The choice of the partition of S i cae-pecific and hould be done by deciion-maker. It i alo poible to conider many partition, a will be hown later. Note that the eto power i till preent, but it i now conferred on the ector group. In both the formulation the ector alue are normalized to in order both to expre the global alue a improement (>1) or worening (<1) with repect to the reference alternatie A0 and to filter out the releance of the abolute alue of the ector alue. In other word, the global alue V j, A expree the relatie improement with repect to A0, rather than the abolute one. Comparing the clae Once the global alue hae been computed for all the alternatie of a gien cla, with either Formulation 1 or 2, they are preented in a plot (Fig. 2), where they appear on the y-axi and the alternatie on the x-axi, the latter ranked for decreaing alue. We will ue the term ranking to refer to thi plot. The comparion of the ranking of the different clae of alternatie i the upport for deciion-maker in chooing one cla. The comparion may be baed on qualitatie metric, which take into account: the dominance among the clae, i.e. the ditance between the ranking, the exitence and the poition of their poible interection; the dominance of each cla with repect to the global alue of alternatie A0; the ranking lope. We hae not yet deeloped any formal procedure for comparing ranking, ince it definition will require the analyi of a ufficient large number of cae. At the preent time, we only hae a few and therefore the comparion can only be baed on intuition. For that reaon we will conider it for the cae of Lake Maggiore only. APPLICATION TO LAKE MAGGIORE WATER SYSTEM Formulation 1 can be directly applied to the planning problem, while Formulation 2 require a preiou definition of a partition of the ector et S. Two alternatie were conidered: Formulation 2a, partition by nation: it i the mot natural one, ince it reflect the point of iew of the intitutional deciion-maker: Italy and Switzerland in our cae. The rationale i that the goernment are willing to accept trade-off among the ector of their nation, but are reluctant to conider cro-border compenation; Formulation 2b, partition by theme: energy, irrigation, economy, enironment, uptream flood, downtream flood were the group conidered. Figure 2 report the ranking for clae A, B and C, uing Formulation 1 (Fig. 2.1), Formulation 2a (Fig. 2.2a) and Formulation 2b (Fig. 2.2b) when the preent (tationary) cenario i conidered. The horizontal line i the global alue of alternatie A0. On the bai of the qualitatie metric we mentioned in the preiou ection, it can be noted that: (1) In all the figure, cla C outperform the other two clae, while cla B appear to be of no interet ince the global alue it produce are nearly alway lower than the one produced by cla A. Thi fact wa confirmed alo when the climate change cenario were conidered (ee below), and therefore cla B will not be hown in the following figure, to implify the 0

5 536 M. Micotti et al. Fig. 1 Stationary cenario: ranking with Formulation 1, 2a and 2b. Fig. 3 Climate change cenario: ranking with Formulation 1, 2a and 2b. iualization. (2) In all the clae at leat 300 alternatie with a global alue higher than A0 exit and, when Formulation 2a i adopted, almot all the alternatie perform better. (3) In Fig. 2.1 ome alternatie caue null atifaction for at leat one ector (V 1 = 0), i.e. the eto power i exerted, while the ame doe not occur for any group in Fig. 2.2a and 2.2b. (4) The teeper lope of the ranking in Fig. 2.2b, with repect to Fig. 2.1 and 2.2a, reeal that the global alue i more enitie to the regulation policie when Formulation 2b i adopted. In concluion, a far a the tationary cenario i conidered, cla C appear to be definitiely uperior to the other one. That i due to the large dicharge capacity it create by dredging a tretch of the Rier Ticino and to the exitence of management policie that preent the downtream rik that uch an increae might potentially create. Thi concluion will now be teted for climate change ituation. Figure 3 how the reult for that cae. For each cla the central line i the median and the grey emi-tranparent area the range within the 25th and the 75th percentile (uncertainty range) of the global alue of the 10 alternatie that hae the ame ranking poition in the 10 cenario. On the bai of the qualitatie metric, one can note: (1) with all the formulation, cla C outperform cla A: there are no interection between the two median and the uncertainty range are almot alway eparate, epecially in the cae of Fig. 3.1 and 3.2a. (2) A comparion of each of the three figure with the correponding one in the cae of tationary cenario, reeal that the global alue are now alway lower than before (exception made for the extreme upper boundary of Fig. 3.2a). In other word the climate change will negatiely affect ector atifaction. Notwithtanding thi fact, in cla C there a ignificant number of alternatie that outperform alternatie A0 till exit, while only few alternatie are uch in cla A when Formulation 1 i conidered (Fig. 3.1) and none exit when conidering Formulation 2b (Fig. 3.2b). (3) A for the tationary cenario, Formulation 2a (Fig. 3.2a) offer a more optimitic point of iew: both for cla A and cla C a ignificant number

6 Strategic deciion making under climate change: a cae tudy on Lake Maggiore water ytem 537 of alternatie outperform A0. (4) Finally, the ranking of the two clae in all the figure hae quite teep lope, highlighting once more that the choice of the regulation policy can make the difference. In concluion, cla C appear to be definitiely uperior to the other one. CONCLUSIONS We propoed a way for comparing clae of alternatie, characterized by the ame tructural interention, under climate change condition. The key element i the comparion of the ranking of the alternatie of the different clae with repect to the global alue they produce, a computed by a uitably formulated global alue function. Different formulation can be conidered either to better repreent the cae-pecific deciion making tructure or to perform a enitiity analyi of the final reult. The application of thi method in the Lake Maggiore cae tudy indicate that the modification of the barrage and the dredging of the lake outlet (cla C of alternatie) outperform any modification of the regulation policy alone (cla A) or of both policy and regulation range (cla C). Moreoer cla C i the only one that offer adaptation poibilitie when climate change cenario are conidered. Uing alternatie global alue formulation doe not change thi reult, confirming it robutne. Reearch i ongoing for trengthening the propoed method, namely for etablihing a formal definition of the quantitatie metric for comparing ranking. Acknowledgement The reearch wa financed by the Action in the context of Project STRADA-INTERREG Italy Switzerland Program, funded by the European Union. REFERENCES Bellman, R. (1957) Dynamic Programming. Princeton Unierity Pre. Da Deppo, P. and Salandin, L. (2006). Studio degli effetti di una modifica dell incile del Lago Maggiore e dell opera di regolazione u portate e lielli del fiume Ticino e del fiume Po.Parte b: analii del manufatto regolatore. Technical report, AIPO. Intergoernmental Panel on Climate Change IPCC (2007) Climate Change 2007: The Scientific Bai. Cambridge Unierity Pre. Keeney, R. L. and Raiffa, H. (1976) Deciion with Multiple Objectie: Preference and Value Trade-off. John Wiley & Son. Pal, Jeremy S., et al. (2007) Regional Climate Modeling for the Deeloping World: The ICTP RegCM3 and RegCNET. Bull. American Meteorological Society 88, Raazzani, G, et al. (2008) Validation of FEST-WB, a continuou water balance ditributed model for flood imulation. In: Proceeding of XXXI Italian Hydraulic and Hydraulic Contruction Sympoium. Reed, M. S. (2008) Stakeholder participation for enironmental management: A literature reiew. Biological Coneration 141(10), Soncini-Sea, R., Catelletti, A. and Weber, E. (2003) A DSS for planning and managing water reeroir ytem. Enironmental Modelling & Software 18(5), Triantaphyllou, E. & Baig, K. (2005) The impact of aggregating benefit and cot criteria in four MCDA method. IEEE Tranaction on Engineering Management 52(2),