A Survey of Economic-Ecological Models

NOT FOR QUOTATION WITHOUT THE PERMISSION OF THE AUTHORS

A

SURVEY

OF EONOYIZC-ECOLOGICAL MOD-

Leon C. &aat

Wal F. J. van L i e r o p

November 1985 CP-85-46

This project was jointly sponsored by t h e Dutch National Research Programme f o r Environmental Health (Lasom) and t h e International Institute for Applied Systems Analysis (IIASA), Austria.

Collaborative h p e r s r e p o r t work which has not been performed solely

at

t h e International Institute for Applied Systems Analysis and which has received only limited review. Views o r opinions expressed herein do not necessarily r e p r e s e n t those of t h e Institute, its National Member Organizations,

or

o t h e r organizations supporting t h e work.

INTERNATIONAL INSTITUTE; FOR APPLIED SYSTEMS ANALYSIS 2361 Laxenburg, Austria

AUTHORS

Leon C.

Braat

and Wal F.J. van Lierop from t h e F r e e University, Amsterdam,

car-

r i e d out t h i s s u r v e y while working as p a r t time Associate S c h o l a r s

at

IIASA (1983- 1984) in a joint e f f o r t between t h e Free University and IIASA's Adaptive Resource Policies P r o j e c t .

Leon C.

Braat

i s a systems ecologist. and h a s c a r r i e d out most of his p a s t r e s e a r c h in environmental policy analysis, e n e r g y analysis, and simulation modeling. He i s c u r r e n t l y with t h e Institute f o r Environmental Studies

at

t h e F r e e University. W a l F.J. van Lierop i s a n economist. He i s with t h e Economic and Social Research Insti- t u t e of t h e F r e e University as p r o j e c t l e a d e r f o r r e s e a r c h on environmental, re- gional and urban, t r a f f i c and t r a n s p o r t a t i o n , and l a b o u r market economics. Both a u t h o r s have a s t r o n g modeling background.

FOREWORD

I am pleased t o have played a very small p a r t in facilitating t h e publication of this survey of economic-ecological models by Leon C.

Braat

and Wal

F.J.

van Lierop. In f a c t , t h e manuscript w a s largely completed before I a r r i v e d

at

IIASA, and thanks should go especially t o C a r l Walters and Dennis Meadows, who were t h e main IIASA contacts during t h e study.

This r e p o r t includes information on t h e c u r r e n t

state

of economic-ecological models in a variety of countries and applications. A s a result, i t will b e a valuable r e f e r e n c e o v e r many y e a r s t o come.

R.E. Munn Chairman

Environment Program International Institute f o r Applied Systems Analysis

This p a p e r r e p o r t s on a survey of economic-ecological models conducted by a r e s e a r c h

t e a m

from t h e Institute f o r Environmental Studies, F r e e University, Am- sterdam (IvM) in cooperation with and supported by t h e International Institute f o r Applied Systems Analysis (IIASA), Laxenburg Austria.

The p a p e r attempts t o describe t h e state-of-the*rt in economic-ecological modeling as derived from this survey. Various classifications have been used t o this end. These a r e :

Classification of economic-ecological policy issues

Classification of phases in economic-ecological policy analysis

Classification of mathematical models used in t h e interface between economics and ecology

Classification concerning t h e internal s t r u c t u r e of mathematical models Classification concerning t h e relationships between economic and ecolog- ical models.

A combination of t h e s e classifications provides a framework f o r evaluating economic-ecological modeling. Special attention i s paid

to

problems t h a t economic-ecological modeling is still facing today, and some r e m a r k s are made on t h e perspectives of economic-ecological modeling.

In a n extensive Appendix a catalogue of model summaries i s presented. These summaries give

a

non-mathematical description of t h e model s t r u c t u r e , model pro- p e r t i e s and t h e policy issue f o r each of t h e documented survey models. Refer- ences t o t h e model documentation a r e included.

The essence of this r e p o r t will a p p e a r shortly in

a state

of t h e art book*, edited by t h e authors of this p a p e r . In addition, i t will include introductions t o economic, ecological and environmental modeling and analysis of integration tech- niques between economic and ecological submodels. The book will f u r t h e r contain a number of c h a p t e r s presenting evaluations of models considered representative f o r those used in various fields of policy and management. The book has been designed t o present a coherent p i c t u r e of t h e origins,

state

and f u t u r e of economic-ecological modeling.

* B r a a t , L.C. & W.F.J. v a n L i e r o p ( e d s . ) (1986) Economic-Ecological Modeling

fw

Environmental and Resource Management, North-Holland Publishing Company, Amstedam ( i n p r e s s ) .

-

vii

-

W e would like t o e x p r e s s o u r g r a t i t u d e t o t h e Dutch National Committee f o r Environmental Health R e s e a r c h and t h e International Institute f o r Applied Systems Analysis (IIASA) f o r funding t h i s r e s e a r c h p r o j e c t .

Acknowledgements are due t o S.W.F. van d e r Ploeg f o r his contributions in s t a r t i n g t h e p r o j e c t and t o L. Hordijk, D. Meadows, P. Nijkamp, and C. Walters f o r t h e i r comments and suggestions. An advisory group of scientists and policy a d v i s e r s helped u s in setting t h e c o u r s e of t h e p r o j e c t . This group included J.

Kindler, T.R. Lakshmanan, H.T. Odum, P. P e a r s e , and t h e above-mentioned scho- lars.

The extensive administrative work involved in this p r o j e c t

was

conducted with g r e a t competence by S. Wilson of IIASA. A t IvM, w e should like t o thank K.

George-Couvret f o r typing e a r l i e r manuscripts during t h i s p r o j e c t , and t h e many s e c r e t a r i e s

at

IIASA involved in typing t h i s p a p e r , in p a r t i c u l a r S. Jandl.

TABLE OF CONTENTS

1. INTRODUCTION

1.1 The Economic-Ecological Modeling P r o j e c t 1.2 Survey Response and Representation 1.3 S t r u c t u r e of t h e P a p e r

2. GENERAL DISTRIBUTION OF ANSWERS

2.1 Geographical Distribution of t h e Models 2.2 Purpose of t h e Economic-Ecological Models 2.3 Fields and Extent of Application

2.4 Model Testing

2.5 Types of Economic-Ecological Models 2.6 Model C h a r a c t e r i s t i c s

3. ECONOMIC-ECOLOGICAL MODELS 3.1 Introduction and Definitions

3.2 Characteristics by Type of Economic-Ecological Models 3.3 Fields of Application of Economic-Ecological Models

4. POLICY ISSUES AND ECONOMIC-ECOLOGICAL MODELS 4.1 Introduction

4.2 Policy Issues and Model Characteristics 4.3 Policy Issues and Fields of Application 5. POLICY ISSUES AND MODEL STRUCTURE

5.1 Introduction

5.2 A Framework f o r Selection of Models

6. PROBLEMS AND PERSPECTIVES IN ECONOMIC-ECOLOGICAL MODELING 6.1 Introduction

6.2 Analytical Problems 6.3 Empirical Problems 6.4 Policy Problems

6.5 P e r s p e c t i v e s of Economic-Ecological Modeling 7. CONCLUSIONS

APPENDIX I: CATALOGUE OF MODEL SUMMARIES APPENDIX 11: QUESTIONNAIRE

A

SURYEY

O F EONOMIC-ECOLOGICAL MODEIS Leon C. B r a a t a n d Wal F.J. van Lierop

1. INTRODUCTION

1.1. The

Economic-Ecological Modeling Project

In 1982, t h e Institute f o r Environmental Studies, F r e e University, Amsterdam (IvM) s t a r t e d a r e s e a r c h project concerning t h e relevance of economic-ecological models f o r environmental policy. In August 1982, t h e International Institute f o r Applied Systems Analysis (IIASA) a g r e e d

to

join IvM in t h i s project.

The main aims of t h e p r o j e c t

were

defined as:

an international survey of economic-ecological models, and a n evaluation of these models.

Within t h e s e aims a distinction

w a s

made between:

scientific aims, and policy aims.

The scientific purpose of t h e international survey was

to

make a n inventory of:

t h e types o r classes of models in different problem fields, t h e kind of s t r u c t u r e and specifications they have, and t h e frequency distribution of different types.

The scientific evaluation purpose concentrated on:

t h e levels of sophistication t h e models have reached,

comparison of t h e various models by field, in o r d e r t o discover gen- e r a l and specific f e a t u r e s ,

problems, and

"hot" r e s e a r c h items.

Policy r e l a t e d purposes of t h e survey

were:

t h e assessment of t h e actual (and potential) use of t h e models, and f u r t h e r

t o analyze who applied them, in which context, and

with what kind of policy objectives.

The policy evaluation purpose concentrated on t h e evaluation of t h e effec- tiveness of t h e applied economic-ecological models. The method chosen t o acquire t h e available information on economic-ecological models and t h e i r applications in- cluded a questionnaire, a survey l i t e r a t u r e study, communication with modelers and policy advisers, and

a

Workshop on Economic-Ecological Modeling (December 12-14, 1983),

at

IIASA.

A generally accepted definition and classification of economic-ecological models was not available

at

t h e

start

of t h e project. W e t h e r e f o r e used a prelim- inary dqj5nition that w a s given as: a set of mathematical rela o n s h i p s describing a n y connections between economic a n d ecological systems.

d

This de- finition w a s communicated to all t h e participants in t h e project. Models in environ- mental economics and environmental biology were not excluded, because w e could not tell in advance whether they contained anything t h a t could be described and would be accepted a s ecological and economic, respectively. W e shall come back t o t h e definition problem in Section 3.

A description and evaluation of a

set

of models can only be rendered accessi- ble and intelligible with a n effective classification system used t o aggregate t h e in- dividual models. W e have t h e r e f o r e developed a simple classification system, which w e found effective in analyzing and evaluating t h e models. This classifica- tion is introduced in Section 2.

1.2.

Survey Response and Representation

During October and November 1982, approximately 200 questionnaires (see Appendix 11) with

a

background paper* were mailed

to

modelers thought t o be in- volved in economic-ecological modeling. Additional questionnaires w e r e sent out t o people suggested by t h e initial respondents, t h e National Member Organizations of IIASA, and o t h e r people who expressed interest, bringing t h e total up

to

350.

Analysis of t h e response s t a r t e d a f t e r t h e final deadline of April 15, 1983. Addi- tional information f o r t h e project was also received in t h e form of detailed model descriptions in r e s e a r c h r e p o r t s and published papers, which had been requested in t h e questionnaire.

Of t h e 354 scientists who received a questionnaire, 123 (almost 35%) respond- ed; 1 6 of them (5%) reported t h a t they

were

no longer involved in economic- ecological modeling, 1 9 o t h e r s (5%) showed interest in the project but did not answer t h e questionnaire f o r various reasons (for instance, because of being

a

theoretician in t h e field o r because they felt t h a t t h e i r model w a s not a truly in- tegrated model). A total of 109 questionnaires were completed by 88 scientists (25%). Many people reported not only f o r themselves but represented a team; a s

a

result 30 modelers (11%)

are

indirectly involved in t h e survey. Consequently, 36%

of t h e scientists originally contacted

are

represented, while t h e total response i s 46%. The non-response

rate

i s 189 (53%), which includes those who never respond- ed and those that responded a f t e r t h e deadline. The remaining 1% includes respon- dents from IIASA and IvM.

Unfortunately, some questionnaires had t o b e excluded. This w a s due, among o t h e r reasons, t o t h e fact that in these cases e i t h e r theoretical model concepts only, o r a monodisciplinary economic o r ecological model were represented. This brought t h e survey sample back t o exactly 100. The results represented in this r e p o r t are based on this number of questionnaires. However, even within these 100 questionnaires, several had t o be excluded in t h e analysis of some of t h e ques- tions. Consequently, t h e total number of valid answers differs among questions.

The extent t o which t h e results are representative f o r t h e e n t i r e area of economic-ecological modeling i s not clear. The initial mailing list f o r t h e survey was derived from IIASA and IvM files. A second wave of questionnaires w a s mailed in early 1983 t o people who were suggested by respondents of t h e f i r s t wave. In

*Braat, L.C. & W.F.J. van Lierop, (1982), Economic-Ecological Models: A background picture. Infor- mal paper, IIASA, Laxenburg, Austria, October 1982.

o u r opinion, a f a i r r e p r e s e n t a t i o n of t h e

area

of economic-ecological modeling w a s obtained.

1.3. S t r u c t u r e o f

the

P a p e r

In Section 2, t h e distribution and frequency of t h e answers p e r question of t h e questionnaire ( s e e Appendix 11)

are

shown. Twelve t y p e s of economic-ecological models h a v e been distinguished by combining questions 5.1 a n d 5.2. The c h a r a c - t e r i s t i c s and fields of application of e a c h of t h e s e twelve t y p e s

are

p r e s e n t e d and discussed in Section 3. In Section 4,

a

classification of policy issues f o r which models may b e developed i s introduced. This classification i s subsequently used t o analyze tendencies in p r o p e r t i e s a n d fields of application of t h e s u r v e y models developed f o r p a r t i c u l a r t y p e s of questions and policy issues.

In Section 5 , w e d e s c r i b e t h e model s t r u c t u r e of t h e s u r v e y models by policy issue class and p r e s e n t a tentative framework f o r t h e selection of a p p r o p r i a t e model s t r u c t u r e s f o r p a r t i c u l a r policy issues. Section 6 discusses problems and p e r s p e c t i v e s in economic-ecological modeling. A g e n e r a l review a n d conclusions are given in Section 7 .

2. GENERAL DISTBIBUTION OF

ANSWERS

2.1. Geographical Distribution o f

the

Models

The geographical distribution of t h e survey sample i s p r e s e n t e d in Table 1 ; 2 3 models came from Western Europe, 6 from Scandinavia, 15 from E a s t e r n Europe, 40 from North America, 2 from South America, 9 from Australia, 3 from Japan, and 2 from Israel.

2.2. P u r p o s e o f

the

Economic-Ecological Models

Models in g e n e r a l have t h e p u r p o s e of documenting and understanding systems of t h e real world. solving problems, a n d predicting consequences of human activi- ties. This, of c o u r s e , i s a l s o

true

f o r models in which both economic a n d ecological components. p r o c e s s e s , and activities

are

r e p r e s e n t e d . T h r e e a l t e r n a t i v e pur- poses have been distinguished:

1. A n a l y t i c a l I n t e r e s t : The model h a s been developed f o r academic pur- poses. I t may, of c o u r s e , have potential f o r application in a policy con- t e x t ;

2. a e m c P o l i c y Problems: The model h a s been developed f o r small-scale short-term policy problems;

3. General P o l i c y I s s u e s : H e r e l a r g e r systems and long-term policy and planning

are

c h a r a c t e r i s t i c s . The output will most likely b e indications of t r e n d s , r a n g e s in predictions, guidelines, and standards.

Question 2 d e a l t with t h e s e a l t e r n a t i v e purposes. The distribution of t h e answers i s p r e s e n t e d in Table 2.

T a b l e

1.

Country of Origin o f Models Included in t h e S u r v e y

Country Number of Models

Argentina 1

Australia 9

Belgium 1

Brazil 1

West Germany 6

Canada 1 0

Czechoslovakia 6

East Germany 1

France 3

Great Britain 4

Hungary 5

Israel 2

Italy 1

Japan 3

The Netherlands 6

Norway 2

Austria 2

Finland 1

Sweden 3

USA 3 0

USSR 3

(21 countries participated) Total 100

T a b l e 2. P u r p o s e of Economic-Ecological Models

Types of Answers C

Total valid cases: 100

X X

a. Application t o a general

policy issue

X ' X 3 5

4 6

3 5

)i

--- ^x

b. Application t o a specific (policy) case

c. Analytical interest (only

potential relevance for policy)

X

^{l x ---} !

^X

^X

X

---i--- X

2.3. Fields

and Extent

of Application

Fields of a c t u a l o r potential application can b e identified. Twenty-five models from t h e survey

were

designed f o r a specific field, t h e 75 o t h e r models are more g e n e r a l and are used in various fields. The fields listed in Question 3.1 (see Table 3 ) r e p r e s e n t fields of planning and decision making in which economic and environ- mental issues have traditionally been dealt with. The list

w a s

not exhaustive, nor fully consistent

as to

t h e level of detail. The option of defining additional fields of application a p p r o p r i a t e t o t h e modeling e f f o r t h a s been used 16 times.

Other fields mentioned

were:

economic development and physical planning

water

pollution

industry (especially food industry) drinking

water

response

to stress

balance of payments transportation housing

economic and environmental policy in g e n e r a l human ecology.

Within a field of application, models may, f o r instance, b e used f o r identifica- tion and description, analysis of complex processes, and prediction of conse- quences of policies, control,

o r

management. Since various models have multiple- use capability in t h i s r e s p e c t , and because t h e s e distinctions

are

sometimes h a r d t o make, t h e s e a s p e c t s have not been included in t h e survey. The questionnaire concentrated on t h e fields

as

such. Table 3 gives a n overview of t h e frequency distribution of t h e s u r v e y models o v e r t h e various fields of application. The d i a g e nal numbers r e p r e s e n t t h e number of models built f o r one field of application only.

For example, t h e f i r s t diagonal element, 2, indicates t h a t only 2 models focus ex- clusively o n a g r i c u l t u r e , whereas a t o t a l of 48 focus on a g r i c u l t u r e in combination with o t h e r fields. The "row" t o t a l gives t h e number of models dealing with a specif- ic field. F o r a g r i c u l t u r e t h i s number i s 50. The various o t h e r elements of Table 3 indicate relationships between the fields of application. For instance, 17 m o d e l s are applied ( o r applicable) both in land use and n a t u r e conservation. It is possible that many of t h e s e 17 models include

more

fields of application. S e v e r a l combina- tions between fields of application

are

quite obvious and consequently o c c u r quite regularly. F o r example, a g r i c u l t u r e with land use, f i s h e r i e s with water, etc. This

P P 4 W Cn a W N P

2

x'

3 F

'?I '=l I-'. 0 x' t-'. 9 3- Y Qrt J lo W Y (D -a a 3- (D i-' . Y ID 0 (D rn Q DO c Y rt rtY rn t-'

.

Y i-'

.

ID ID Le

6

rt 0 rn c J W P P P - P

-

-

- ---

- - -

----

P N --- I- F P N Cn P h, P N F 4 N P Cn 0 & W 0 P a a3 a3 Cn ID Cn V, N 0

Agriculture Forestry Fisheries Land Use Outdoor recreation Energy Nonrenewable res. Nature conservation Diseases Pests Water Soil Air Other TOTAL

might imply t h a t t h e number of models designed f o r specific fields of application i s higher than 25.

Some models have been designed f o r many fields of application. Consequently t h e sum of models in a

row

in Table 3 will usually differ from t h e row

total

f o r a field given in t h e last column. None of t h e models applied in o r applicable f o r out- d o o r r e c r e a t i o n , nonrenewable r e s o u r c e s , n a t u r e , conservation, diseases, pests, soil and

water

were built exclusively f o r t h e s e fields of application.

In general, models are developed from some conceptual framework, often described in t h e form of a

set

of boxes and a r r o w s (diagrams), which have no s t r i c t definitions

or

constraints.

These diagrams, sometimes also called conceptual models, often form t h e basis f o r t h e next s t a g e of model development, in which system components, processes, and relationships are described in a mathematical format. The resulting s t r u c t u r e i s less ambiguous. These m o d e l s in mathematical format, called theoretical by

some

modelers, are operational in t h a t with t h e addition of fictional

or

real world d a t a , some form of quantitative analysis c a n b e made. When t h e s e operational models are subsequently used, they may b e called applied models. Two c a t e g o r i e s have been distinguished in t h e questionnaire in relation

to

t h e purpose of t h e model:

models which have been applied i n a research contezt (e.g.. methodological) only, and those applied i n actual policy formulation or decision making.

Question 3.2 d e a l t with t h e e x t e n t of application. The distribution of answers i s r e p r e s e n t e d in Table 4.

F r o m

t h i s t a b l e w e can see t h a t models applied in

an

ac- tual policy context and models applied in a r e s e a r c h context are equally high in r e p r e s e n t a t i o n in t h e sample (both 36 times). The combination a-c, in which only one

score

i s made, i s probably a mistake. I t should b e mentioned t h a t t h e t o t a l number of questionnaires r e p r e s e n t e d in Table 4 i s only 91. This i s due

to

incom- p l e t e answers.

2.4.

Model Testing

The d e g r e e

to

which a model o r i t s output r e p r e s e n t s t h e s t r u c t u r e o r behavior of t h e system i t

w a s

meant t o r e p r e s e n t , c a n b e evaluated in various ways. The r e l a t i v e performance of a model can b e t e s t e d by comparing i t s r e s u l t s with t h e r e s u l t s of o t h e r models calibrated with t h e

same

d a t a input. Statistical and econometrical testing techniques

can

b e of help in t h i s r e s p e c t . A model c a n also b e evaluated by comparing calculated (predicted) values with values measured in t h e real world. Of c o u r s e , t h e measured values t h a t have been used f o r calibra- tion cannot b e used as valid

test

data. Statistical methods (tests) may b e used in deciding t h e significance of t h e difference between p r e d i c t e d values and measured values.

Dynamic simulation models c a n b e r e g a r d e d as t e s t e d when r e p e a t e d success in prediction i s observed. This may b e done by s t a r t i n g t h e simulation at some point in history with adequate (initial) historical conditions and subsequent

assess-

ment of t h e deviation of t h e p r e s e n t values, o r by monitoring t h e real world sys-

t e m s

f o r continuous testing.

Question 4 dealt with t h e issue of model testing. Table 5 gives t h e distribution of t h e answers. Apparently testing against t h e d a t a , o t h e r than used f o r calibra- tion of t h e model, i s t h e most common way of testing economic-ecological models.

The combination b-d

scores

twice, most likely by mistake

or

d u e t o misunderstand- ing.

Table 4.

E x t e n t of Application

Distribution: 2 2 31 18 14 5

1

0 Total valid cases: 91

Type of Answers

^F L

Table 5.

The R e p o r t e d Testing of t h e Survey Models

Distribution: 5 3 2 3 3 0 7 8

2

5 Total valid cases: 9 2

37

5 0

a. Applied in an actual policy context

X

b.

Applied in a research

context X

c. Not yet applied but operational

X

X

---&---A

X

X

X

X

X

X X

--

X

2.5.

Types of Economical-Ecological Models

Economic-ecological models

are

considered t o consist of

at least

one economic and one ecological submodel. I t is, however, a l s o possible t o have s e v e r a l econom- i c submodels connected t o one

o r

s e v e r a l ecological ones. The internal s t r u c t u r e of t h e submodels can b e defined by t h e form of t h e internal relationships between t h e variables. Only two t y p e s have been distinguished in Question 5.1:

1.

a

submodel consisting of s e p a r a t e , isolated variables only ( ' s n , simple submodel), and

2. a submodel containing a

set

of variables which

are

fully,

o r

partially, in- t e r r e l a t e d ('c' , complex submodel).

Economic-ecological models t h a t have only one elaborately developed submo- d e l linked

to

a single index ( o r

set

of independent indices) representing t h e o t h e r system, or a submodel t h a t is driven by one, o r s e v e r a l , exogenous, independent variables from t h e o t h e r system, can b e considered

as a

group in which t h e s e two types

are

mixed. Among t h e 81 valid cases t h e r e

are:

1 6 simple eaonomic submodels 9 simple ecological submodels 65 complex economic submodels 72 complex ecological submodels

and t h e following combinations:

simple economic

+

simple ecological submodel : 4 simple economic

+

complex ecological submodel : 12 complex economic

+

simple ecological submodel : 5 complex economic

+

complex ecological submodel : 6 0

Apart from being classified by t h e r e l a t i v e complexity of t h e internal s t r u c - t u r e of t h e submodels, economic-ecological models can b e classified f u r t h e r by t h e types of r e l a t i o n s h i p s between t h e submodels. T h r e e types

are

distinguished.

based on t h e direction of t h e relationships (Question 5.2):

1.

a

one-way relationship in which t h e economic submodel d r i v e s t h e ecolog- ical submodel (10 models);

2. a one-way relationship in which t h e ecological submodel d r i v e s t h e economic submodel (19 models);

3.

a

two-way relationship, i . e . interdependent submodels (52 models).

In Table 6 questions 5.1 and 5.2 have been combined to produce 12 types of economic-ecological models.

Table 6. Types of Economic-Ecological Models

simple models

simple economic e x e c o c a models

complex e c o n d c simple ecological mode 1s

complex models

Total

h

Econ

.

^Bcol.

1

1

2

-

m-7

2

Fl,-fq

5

10

Econ. Ecol.

I-7

2

3

F-7

0

F - - 1

47

5 2

Econ. Bcol. Total

r j T

1

- 1 7 1

7

PI-rn

3

F j a - f q

8

19

L

-

4

12

5

2-

6 0

8 1

2.6. Yodel Characteristics

Models c a n b e d e s c r i b e d b y many c h a r a c t e r i s t i c s , t h e i r time a n d s p a c e dimen- sions, t h e i r s i z e , a n d t h e i r function. Where time i s c o n c e r n e d , t h e first distinction made i s w h e t h e r a model h a s time as a v a r i a b l e . If s o , t h e model i s r e f e r r e d t o as dynamic. In Question 6.1 dynamic explicitly r e f e r s

to

t e m p o r a l dynamics. If time i s n o t a v a r i a b l e , models are c a l l e d s t a t i c . One c l a s s of models which d o e s c o n s i d e r time, b u t n o t as a v a r i a b l e , i s s e p a r a t e l y indicated: c o m p a r a t i v e s t a t i c models.

These models d e a l only with time in as f a r as t h e y t a k e i n t o a c c o u n t t h e beginning a n d t h e e n d of t h e p e r i o d f o r which t h e y h a v e b e e n developed. Table 7 p r e s e n t s t h e d i s t r i b u t i o n of a n s w e r s

to

Question 6.1, t h e time dimension of models; "En"

s t a n d s f o r economic submodel, "El" s t a n d s f o r ecological submodel. Dynamic models dominate t h e field; both completely dynamic models a n d models with a dynamic ecological submodel linked t o a s t a t i c or c o m p a r a t i v e s t a t i c economic sub- model are numerous.

Table 7. Dynamics of Economic-Ecological Models

a. Static

X X I

c. Dynamic I

Distribution:

12

6 48

12 6 1 3 1

Total valid cases: 89

Another way of looking at t h e a n s w e r s i s p r e s e n t e d in Table 8.

F o u r g e o g r a p h i c a l scales h a v e been distinguished in t h e s u r v e y : local, region- a l , national a n d global. Global a n d national s c a l e s were c o n s i d e r e d t o p r e s e n t no problems in delineation. Regional models c a n r a n g e from v e r y l a r g e

to

r a t h e r small areas. However, i t was explained in t h e background p a p e r t h a t accompanied t h e q u e s t i o n n a i r e , t h a t t h e y should c o v e r only p a r t of a nation a n d include more t h a n just a c i t y o r a n e c o s y s t e m ( t h e l a t t e r c o n s i d e r e d

to

b e t h e l o c a l s c a l e ) .

Table

8. Total Number of Economic and Ecological Submodels f r o m Various Time Categories.

Economic Submodels Ecological Submodels

a. Static 24 13

b.

Comparative static

c. Dynamic 52 67

--

Total valid cases:

89

*One double-count, due to the coxrbination represented by the extreme right column in Table 7.

Table 9 gives a distribution of t h e various geographical s c a l e s in t h e models.

An a l t e r n a t i v e way of looking

at

time in models, d i f f e r e n t from t h e a p p r o a c h followed in Tables 7 and 8, i s from t h e point of view of t i m e p e r i o d s covered by t h e model, e i t h e r in analysis or in prediction (time horizon). Additional f e a t u r e s t h e n , are t h e time intervals. S i n c e time i s often t r e a t e d differently in economic and eco- logical models, a distinction w a s indicated in t h e questionnaire (Question 6.3). Re- g r e t t a b l y t h e s u r v e y did not supply unambiguous information on t h i s point. Ques- tion 6 . 3 caused much confusion and h a s a low r e s p o n s e score. This should b e t a k e n into account when i n t e r p r e t i n g t h e r e s u l t s t h a t are p r e s e n t e d in Table 10. Because of t h e problems with t h i s question, w e give t h e scores f o r e a c h time a s p e c t for t h e economic a n d ecological submodels s e p a r a t e l y . Combinations are not t a k e n i n t o consideration h e r e . A similarity in economic and ecological submodels i s evident in using a "1" y e a r p e r i o d in t h e i r analysis as well as for t h e i r time i n t e r v a l . Economic submodels seem to have slightly longer time i n t e r v a l s t h a n ecological ones. The horizon of prediction v a r i e s between 20 a n d 30 y e a r s . I t looks as though many models from t h e s u r v e y aim

to

give a forecast for t h e y e a r 2000.

A distinction between optimization models (which contain a n objective func- tion), simulation models, and o t h e r models which h a v e n o internalized o b j e c t i v e s w a s t h e basis f o r Question 6.4. Table 11 p r e s e n t s t h e distribution of t h e combina- tions. The o t h e r models t h a t have been mentioned in t h e questionnaire a r e :

Table 9. The Geographical Scale of Economic-Ecological Models a. Local X X X X X XX X X b. Regional X X X X XX XX X X X X c. National X X X X X D. Global X X

---

Distribution: 22 2 8 8 6 6 2 3 2 2 3 1 2 1 Total valid cases: 86

Table 10. Analyzed Time Periods, Time Intervals, and Predicted Horizons of Economic and Ecological Submodels

1 day 1 wk 2 wks 6 wks 1 mth 2 mths 3 mths 5 mths 6 mths 1 Yr 2 yrs 3 yrs 4 yrs 5 yrs 6 yrs 7 yrs 8 yrs 9 yrs 10 yrs 15 yrs 20 yrs 25 yrs 30 yrs 40 yrs 50 yrs 100 yrs 200 yrs 250 yrs Indefinite Total valid cases :

Covered time period

En E 1

-- Time interval

1

En E 1

Horizon of Prediction

En El

a. input-output models;

b. scenario;

c

.

analytical;

d. statistical functions;

e. decision models.

Because they s c o r e d only a few times, they have not been included in Table 11.

I t should b e mentioned t h a t t h e models in t h i s listing

are

not absolutely exclusive.

Table

11.

Optimization and Simulation of Economic-Ecological Models

Total Total

a. Optimization X X I 1 ^X I ^{X X I X} I X X ( X ( ⁴⁴ 1 ²⁴

b. Simulation _-- 1 _---- ^{X X} _---- ^~ "1 _---- ^{X X} _---- ^{X X L ~} _--- XI ^{X X} 1 ²⁷ 1 ⁴⁷

---L-

---- ---

Distribution: 23 25 12 10 3 6 1 71* 71*

Total valid cases: 80

*Due to double-counting

Economic submodels often use optimization techniques, whereas ecological submodels are applied with simulation techniques t o a g r e a t e r extent. The combi- nation of a n economic simulation submodel with

a

single ecological optimization model does not exist. The o t h e r combination, however, i s quite popular.

One way t o indicate t h e size of a model, r e l e v a n t in both ecological and economic models i s t h e number of endogenous ( s t a t e ) variables. Question 6.5 focused on t h i s model c h a r a c t e r i s t i c . The r e s u l t s are presented in Table 12.

T h e r e a p p e a r s t o b e a g r e a t e r tendency towards small- and medium-sized models r a t h e r than towards l a r g e r models. However, one should note t h a t t h e number of v a r i a b l e s p e r submodel i s indicated. Two submodels of t y p e b may imply close

to

200 variables!

Table

12. Number of Endogenous Variables in Economic-Ecological Models

Distribution: 34 19 4

17 2

5 5 1 2

Total valid cases: 89

3.

ECONOMIC-ECOLOGICAL MODELS

3.1. Introduction and Definitions

In this section, twelve types of economic-ecological models (see Table 6) are characterized and discussed. These -types have been defined based on t h e struc- t u r e and relationships of t h e submodels. Together they give a

m o r e

precise description of t h e preliminary definition of economic-ecological models as given in Section 1.1 of this paper.

Based on t h e results of this survey a more elaborate definition of economic- ecological models has been developed. I t

w a s

assumed t h a t wherever mentioned in t h e questionnaire t h e submodels (economic and ecological) were recognized by t h e respondents as describing t h e respective systems. I t w a s , however, not clear, whether t h e submodels denoted as "simple" would be recognized

as

real ecological o r economic models by any of t h e ecologists o r economists, respectively.

I t a p p e a r s t h a t many modelers consider

an

economic model with a n emission variable as economic-ecological, possibly equating t h e terms "environmental" and

"ecological". In t h e

same

fashion ecological models with a pollutant as input are sometimes called economic-ecological, apparently on t h e grounds t h a t t h e pollutant comes from t h e economic production o r consumption process.

A s t h e IvM-IIASA p r o j e c t progressed, t h e different meanings attached t o t h e term economic-ecological became more t r a n s p a r e n t and e a s i e r

to

distinguish from each o t h e r . It became obvious through t h e study of t h e model documentation t h a t a

"simple" ecological submodel could contain e i t h e r

a

single (or s e v e r a l indepen- dent) pollution indicator(s) o r biotic variables such as animal population o r vege- tation biomass. Depending on t h e definition of "ecological", t h e submodel would be considered

as

such. If "ecological" implies

a

related

set

of variables, then none of t h e simple submodels should c a r r y t h a t name. If i t implies t h a t next

to

some physico-chemical variables (abiotic)

at least

one biotic variable should be includ- ed, then some of t h e 'simple' ecological submodels

are

not ecological but physico- chemical only. Furthermore, even some 'complex' ecological submodels may not be truly ecological if t h e

latter

meaning is followed. These considerations f o r t h e ecological submodels have t h e i r c o u n t e r p a r t on t h e economic side.

In summary, not all t h e models in t h e model s t r u c t u r e classes where a simple and a complex submodel

are

combined, can b e called integrated economic- ecological models.

In o u r definition, complex, i n t e g r a t e d economic-ecological models consist of submodels which

are.

accepted as adequately describing t h e s t r u c t u r e (and behavior) of economic and ecological systems respectively,

as

w e l l as t h e

struc-

t u r e and functioning of t h e interrelationships between t h e two systems. Models in which one of t h e two kinds of submodels consists of a n internally unrelated

set

of variables (combinations of simple and complex submodels) could still be called econonic-ecological if this loose

set

of variables i s accepted

as

a

clear

c h a r a c t e r - ization of key-elements of t h e pertinent scientific discipline.

Models in which t h e latter condition i s not

m e t

should, however, not be called economic-ecological. The various models in this group may still b e recognized

to

f i t in t h e r e a l m of environmental economics, environmental biology, r e s o u r c e economics, o r r e s o u r c e ecology. Although these kinds of models were not excluded in t h e survey (i.e.,

as was

s t a t e d explicitly in t h e p a p e r accompanying t h e ques- tionnaire f o r environmental economic, and environmental biological models) only relatively f e w questionnaires could clearly b e identified

as

representing any one of them.

The twelve types of economic-ecological models (see section 2.5) have been combined into four classes of models on t h e basis of t h e complexity of t h e submo- dels and each with t h r e e types of relations between economics and ecology. The f i r s t class, simple models, is only represented by 4 models. This does not provide enough information f o r unambiguous conclusions. The same is t r u e f o r t h e t h i r d class, complex economic plus simple ecological submodels; h e r e only 5 models are available

to

c h a r a c t e r i z e t h e class. In t h e second class (complex ecological with simple economic submodels) and t h e fourth class (complex economic-ecological models) 1 2 .and 60 models are included respectively. The discussion w i l l mostly refer t o these two classes of models. For each of t h e twelve types

w e

have sum- marized t h e s c o r e s on model p r o p e r t i e s such

as

application, testing, dynamics, technical purpose (intended use, i-e., optimization o r simulation), model size, and geographical scale of t h e system modeled.

3.2. Characteristics by Type of Economic-Ecological Models

In Table 13, t h e distribution of p r o p e r t i e s o v e r t h e twelve types of economic- ecological models is presented. Scores are indicated p e r model type and aggregat- ed p e r class of models. The majority of t h e types and

classes

of models r e p r e s e n t - ed in t h e survey have been applied in

a

general o r specific policy case. The ma- jority of t h e models in classes 2 and 4 have also been tested in one way o r another (see Table 5), 91X in class 2 and 68.5% in class 4.

-

¹⁸

-

Table 13.

Properties of Economic-EcologicaI Models

Y = yes ST = static OP = optimization ME = medium RE = regional N = no CS = comparative static SI = simulation LA = large N A = national MI = mixed DY = dynamic SM = small LO = local GL = global

Geographical Scale

B-m

Complex Models

LO

1

1 1

Size

4

2 9

3 7

SM

1 1

1 purpose

1 1

4 1 8

1 2

c

Submode 1s Economic Ecological

El--El

m

H-+l

Simple Models

Dynamics

1 5

1 7 2 7

3 7

ME RE

1 MI

1 1

OP

1 Tested?

L A NA GL

ST 1

1

SI

1

1 1 1 1 1 3 1

1

Applied?

Y 1

1 2

MI

1

1 DY

1 CS Y

1

2

1 4

N

2

2 2

3

4

MI

1 N

3

6 3 2

3 7

2 2 1 1 1 2 1 1 2 1

8

1 2 1 4

1 6 1 4

1 8 1 6

2 4 2 1 3 4 2 4 2 2 4

2 2 1 6

1 9 2 5

2 9 3

7 1 2

1 5

2 1 1 1

1 2

1 7 6

7 6

6 2

9

2 1 3

I

The distribution of dynamic models in class 2 may a p p e a r odd; 9 out of 1 0 a r e mixed dynamichtatic o r dynamic/comparative static. However, all ecological sub- models in this class are dynamic, and all economic (simple) submodels but one are not dynamic. In class 4, completely dynamic models dominate (63%). More than 76%

of t h e ecological submodels and 67% of t h e economic submodels

are

dynamic. Only 4 (out of 59) models in this class are completely static. Given t h a t classes 1 and 3 do not offer

a

strong counter argument within this survey, i t seems t h a t the w a y to go i n economic-ecological modeling i s d y n a m i c , especially since t h e majority ap- p e a r s

to

b e tested and is applied in some context.

A s

to

(the distribution of) prescriptive (optimization) and descriptive/- predictive (simulation) models, t h e r e is onLy a s l i g h t l y greater number of p u r e s i m u l a t i o n models t h a n p u r e optimization models, w h i l e mizsd t y p e s a r e as common as s i m u l a t i o n models. The ecological submodeld a r e , in most cases, simu- lation models (83% in class 2, 71% in class 4). The economic submodels use optimiza- tion techniques in only 33% of t h e cases in class 2, but 62.5% in class 4.

Large models, defined as having

at

least one submodel with more than 100 en- dogenous variables,

are

relatively seldom used (8.5% in class 2, 13% in class 4, 14.5% overall). Most modelers a p p e a r

to

use models of medium size, defined as hav- ing submodels with up

to

100 endogenous variables, while t h e

small

models (i.e., submodels with less than 1 0 endogenous variables)

also

o c c u r quite frequently.

The next model c h a r a c t e r i s t i c in Table 13 is t h e geographical scale of t h e sys-

t e m

f o r which t h e models were developed. The survey did not produce many models for national and global systems. Given t h e problem of t h e representativeness of t h e sample, w e feel t h a t conclusions cannot b e drawn yet about t h e lack of economic-ecological integration

at

t h e important national level.

I t is obvious from t h e numbers in Table 13 t h a t t h e most common geographi- cal scales for modeling a r e regional a n d local. The focus on local and regional systems is even s t r o n g e r than c a n be concluded from Table 13, since 9 out of 13 (in class 4, and 2 out of 4 in class 2) "mixed scales" models

are

combinations of region- al and local.

3.3. Fields o f Application o f Economic Ecological Models

In Table 14, t h e fields of application of economic-ecological model types are indicated.

It

should b e noted t h a t , as remarked in relation

to

Table 3, many modelers have indicated t h a t t h e i r models

are

applicable o r applied in more than one field. The survey sample of models evidently c o v e r s

a

broad r a n g e of applica- tion fields (see also section 2.3). From t h e survey, i t h a s not become clear which types of models are s t r i c t l y developed f o r specific fields. However, t h e following observations may clarify t h e situation shown in t h e Table.

"Simple" ecological submodels are not found in applications in agriculture, forestry, nature conservation, diseases, p e s t s and soil. They are only r a r e l y used in fisheries ( 1 out of 19), land use (2 out of 38), outdoor r e c r e a t i o n ( 1 out of 15) and

water

problems (1 out of 43). "Simple" economic submodels a p p e a r not t o b e used in applications for problems of non-renewable r e s o u r c e s , and only in 1 out of 20 cases for energy problems and 1 out of 1 4 cases f o r

air

problems. In t h e sur- vey, t h e "simple" ecological submodels form only 11% of t h e ecological submodels, and t h e "simple" economic submodels only 30% of all economic submodels. This im- plies t h a t these observations can hardly b e taken as a basis f o r t h e state-of-the-

art.

Table

1 4 .

Fields of Application of Economic-Ecological Models

T o t a l 4 3 B 1 9 38 1 5 2 0 1 6 24 4 1 0 4 3 2 0 1 4 1 4

Given t h a t t h e complex economic-ecological m o d e l s with two-way connections form 58% of t h e sample, a

closer

look

at

t h e s e models r e v e a l s t h a t they are used relatively

more

often in all applications e x c e p t diseases (only 25%). A s t o agricul- t u r e , 58% of t h e applications are complex two-way economic-ecological models, in o t h e r fields more t h a n 71% (up t o 87.5% in f o r e s t r y ) .

Again, t h e sample i s such t h a t no f a r reaching conclusions c a n b e drawn from t h i s analysis. I t i s y e t r e m a r k a b l e t h a t t h e most complex t y p e of model dis- tinguished in t h e s u r v e y i s applied t o such a g r e a t e x t e n t in most traditional fields of application.

4.

POLICY ISSUES AND ECONOMIC-ECOLOGICAL MODELS

4.1. Introduction

In general, models are e i t h e r built f o r academic o r f o r policy purposes. Ac- cording

to

Websters Dictionary

a

policy is defined as: (1) a definite c o u r s e of or method of action, s e l e c t e d from among a l t e r n a t i v e s and in light of given conditions

to

guide and determine p r e s e n t and f u t u r e decisions; (2)

a

high-level o v e r a l l plan, embracing t h e g e n e r a l goals a n d a c c e p t a b l e procedures.

Policy making i s t h e n considered t o b e t h e p r o c e s s of shaping policy (i.e., planning), plus t h e a c t u a l choice between a l t e r n a t i v e (i.e., decision making) and t h e implementation of t h e s e l e c t e d a l t e r n a t i v e s (i.e., management). Both planning and management involve t h e prediction of impacts and developments in t h e system as t h e basis f o r evaluation a n d choice.

In environmental policy making t h r e e main t y p e s of p o l i c y objectives c a n b e distinguished:

1. Nature conservation objectives (summarized e.g

.

^{, as} minimum exploita- tion and damage of ecological systems);

2. Economic objectives (expressed, f o r example, as maximum production of goods and s e r v i c e s from ecological systems

at

t h e minimum cost);

3. Mixed objectives ( f o r example, maximum sustainable use of r e s o u r c e s , i.e., material, e n e r g y a n d information r e s o u r c e s , and s p a o e and environ- mental s e r v i c e s ,

at

minimum ecological damage and minimum cost).

Policy making involves e i t h e r a single objective o r various objectives. In- tegrated policy making

at

t h e i n t e r f a c e of economic a n d ecological systems is mul- tiobjective by definition. Policy i s s u e s

are

t h e policy

or

managerial questions

or

problems t h a t are a d d r e s s e d with one of t h e s e t h r e e t y p e s of objectives in mind.

For t h e evaluation of effectiveness of t h e d i f f e r e n t t y p e s of economic- ecological m o d e l s in a s s o r t e d policy applications,

a

classification of policy issues i s required. W e t h e r e f o r e introduce a clasdJ%cation oj'policy i s s u e s . I t i s based on a conceptual s e p a r a t i o n of t h e economic system from t h e ecological system.

These subsystems are considered t o b e connected by flows of m a t t e r , e n e r g y a n d information ( s e e Figure 1 ) .

The classification developed from t h i s simple concept of

t w o

subsystems and t h e i r connecting flows, consists of t h r e e classes, e a c h containing t h r e e subclasses.

The t h r e e classes follow t h e division of policy objectives mentioned above. The t h r e e subclasses

are

based on a distinction between input, output a n d throughput flows, and combinations of these.

Information, material a d energy resources

r -

€cologicel rubsystem

Economic subsystem C

Pollution, human bctivity in weation, construction planning and manepernent

Figure 1. Relationships Between Ecological and Economic Subsystems

The following classes of policy issues have thus been identified:

(a) Ecological Policy

Issue% (see Figure

2)

Class

1:

Ecological impacts of resource nse

The concern h e r e

is

as to what t h e ecological

effects

are of t h e ex- traction of resources from ecosystems (natural and managed) and which policies might lead t o minimization of t h e impacts.

Class 3: Ecological impacts of pollution and disturbance

The issues

are

t h e

effects

of various types of pollutants and of physical damage due t o human activity (such as in recreation and construction). The policies focus on control measures at t h e

re-

ceiving end.

Class

5:

Ecosystem planning and management

This

class

contains issues dealing with total ecosystems throughput.

Management and. more abstractly, t h e planning

of

whole ecosys-

tems, manipulate both inputs and outputs

^as w e l l

as internal struc-

ture.

Figure

2.

Ecological Policy Issues

(b)

Economic Policy

Issues

( s e e Figure 3)

Class

2:

Economic impacts of resource development and exploitation The issues focus on t h e economic a s p e c t s of r e s o u r c e development:

both c o s t impacts and management of development activity'.

Claim

4:

Economic impacts of pollution

Economic a s p e c t s (e.g.

cost

and allocation) of output control, e.g., water pollution c o n t r o l c o s t , including planning a n d management a s p e c t s .

Class 6: Economic system planning and management

In t h i s class t h e issues of optimal allocation of r e s o u r c e input

to

t h e economy a n d aost-effective material balances are expected.

Figure 3. Economic Policy Issues

(c) Economic-Ecological Policy h e s (see Figure 4) Class

7:

Sustainable

use

of resources

The concern is, evidently, how

to

plan and manage r e s o u r c e use ac- tivity (including development) in such a way t h a t a long-term use is guaranteed, considering, e.g., cost aspects and changing demand.

Class 8: Sustainable use of environmental services

The objective h e r e may be phrased as optimal use of t h e ecological carrying and assimilative capacity in an attempt t o plan and manage f o r minimal negative impact of maximal use of t h e s t r u c t u r e and s p a c e offered by t h e ecological systems.

Class 91 Total system planning and management

The issues in this class involve complete cycles of input- throughput-output. The geographical scale (e.g., local and global) may differ as may t h e elements t h a t cycle in (or flow through) t h e system (energy, carbon, phosphates, biomass, pollutants).

4.2.

Policy

b e s

and Model Characteristics

The theoretical classification, presented in t h e previous section has been used

to

classify t h e questions and problems f o r which t h e survey models

were

designed. The questionnaire did not contain a question pertaining t o t h e policy is- sue a t which t h e model w a s addressed, since this a s p e c t of t h e survey w a s intro- duced later in t h e project. W e have t h e r e f o r e attempted t o identify t h e policy is- sues f o r each of t h e survey models through t h e documentation about t h e model and t h e project o r , in some cases, t h e model name. In Table 15 t h e distribution of poli- cy issues of t h e survey models o v e r t h e 9 classes i s given. A s i s obvious from t h e total, 15 studies could not b e classified d u e t o lack of reliable information.

Table 15.

Distribution of Respondents Over Policy Issue Classes

Clam. # U m I of respondent6

1 Ecological iqacts of resource we 5 2 monaric impact6 of rasource developwnt and we

3 Ecological i q a c t . of pollution and blsturbance 4 Econaric impacts of p o l l u t i o n

5 Ecoryrrytr planning and mnagemnt 6 ~ c - c r y s t r planning and ranagemnt 7 Sustainable we of resource6

8 Sustainable une of e n v i r o m n t a l rrervices 9 ~ o t a l s y s t r planning and r a n a g m n t

Total of cases where p o l i c y issues could be amse.sed 8 5

The g r e a t variety of policy issues, o r r e s e a r c h problems, which were found in t h e survey can b e found in Appendix I, t h e catalogue of model summaries. This ca- talogue lists t h e model descriptions by policy issue class. A t f i r s t glance, t h e models which are lumped together from a policy issue point of view look very dif- ferent. In o r d e r t o find out t o what extent similarities existed within and differ- ences between t h e models of t h e 9 policy issue classes, w e have examined t h e pro- perties, c h a r a c t e r i s t i c s , model s t r u c t u r e and fields of application of t h e s e groups of models.

For this analysis w e have chosen t o employ an identical format a s in Table 13 where t h e c h a r a c t e r i s t i c s of model types, classified by s t r u c t u r a l p r o p e r t i e s a r e listed. In Table 16, t h e f i r s t column shows t h e 9 policy issue classes in 3 groups, ecological, economic and economic-ecological policy issue classes.