Development of a volcanic risk assessment

Transcription

1 Development of a volcanic risk assessment information system for the prevention and management of volcanic crisis: stating the fundamentals F. Gomez-Fernandez Consiglio Nazionale delle Ricerche, CS Geol. Strutt. e Dinn. del Appennino, via S. Maria 53, Pisa, Italy gomez@dst.unipi.it Abstract The variety of constraints that conventional methods devised to account for volcanic risk have commonly faced, has limited the successful achievement of this kind of study. The detailed analysis and categorisation of the most common difficulties found by classical volcanic risk assessments has allowed us to identify the basic elements that risk calculation procedures would have to include to become efficient. Due to the operational improvement that the incorporation to the risk assessment context of technologies such as GIS and physical simulation models can provide, the development of a volcanic risk assessment information system for early prevention and management of volcanic crisis has been considered. Because of the lack of a previous extensive background on the application of GIS for these purposes, a previous study aimed at defining the procedures to be followed to analyse volcanic risk in the frame of a GIS has been carried out. In order to test the model devised, a pilot project devoted to assess the risk posed by lava flows at Tenerife island (Canary Islands, Spain) has been then carried out. Although the analysis of the results obtained indicates a good level of achievement of the objectives pursued, the complexity of the resulting calculation structure and the background knowledge required to manage it, make the system devised a tool difficult to master by the users that could eventually benefit of the methodology developed. These facts have called attention upon the need to improve the communication with the system through a customised interface, capable of satisfying the users' basic information requirements. To achieve this new goal, a methodology for object oriented design has been selected to define the basic architecture of the system. 1 Introduction A major aim pursued by classical volcanological studies has been the production of hazard zonation maps on which the potential area of influence of the volcanic phenomena considered and the existing socio-

2 112 GIS Technologies and their Environmental Applications economic data available (such as lifelines, population centres, etc.) are displayed together in order to obtain information about the potential losses in case of a volcanic crisis. The elaboration of such multiple hazard-multipurpose maps (Foster*) has made up a priority requirement for volcanic risk assessments as they serve as the departing point from which the evaluation process begins. The selection of such a complex way to display the information is based on the fact that, commonly, there is more than one phenomenon susceptible to occur at any volcano and that the risks created by each kind of impact pertain to more than one activity. As a result, there is the need to set in advance a clear series of criteria for representation of all the elements and phenomena included to ease the interpretation. Otherwise, it might become a difficult task either because there is an excess of information displayed on the map or a too schematic way to express it. Even taking into account the representation difficulties associated, this mapping approach is, anyway, the most useful to follow when there is the need to develop emergency, prevention and land use plans (Gupta & Joshf). Nevertheless, the elaboration process followed is basically time consuming and expensive due to the large amount of information required to produce these outputs (Alexander*), what makes it difficult to review or update the results of an assessment if unexpected events or new data enter into play in the calculation. Under this perspective, it would be desirable to find a way to review and improve the existing map production methods in order to provide an adequate solution to the current time and accuracy constraints faced by, among other disciplines, volcanic risk assessments (Gupta & Joshf). With this idea, we have considered the incorporation to the risk maps generation process of a specific set of computer based tools,- such as the Geographical Information Systems and the eruptive phenomena physical simulation models -, a feasible and realistic solution of the assessment problems found by classical studies. The final aim pursued by our study is the development of a volcanic risk assessment information system for early prevention and management of volcanic crisis. The process followed to state the fundamentals from which to construct such a system has been the object of this paper and is briefly introduced through the next sections.

3 GIS Technologies and their Environmental Applications A computer based volcanic risk assessment methodology The successful level of performance that GIS methodologies application has provided in other areas of risk assessment (e.g. epidemics control, dispersal of toxic substances, etc.) and the substantial improvement in the knowledge of the behaviour of volcanic phenomena that existing physical simulation models have provided, have served us as the basis to consider that the combination of both tools for volcanic risk assessment purposes might provide a dynamic and powerful way to solve the common constraints to produce information that these studies have usually faced (G6mez-Fern&idez*). GIS can contribute to improve the efficiency with their capacity to (1) store, retrieve and manage the large volumes of data to be analysed, (2) devise automatic data processing routines to allow fast calculation and upgrading of the information and, (3) produce the high quality outputs required for assessment purposes. On the other side, physical models have provided the way to simulate eruptions and to obtain information on the extent and magnitude of their effects (Pareschi & Berstein*), having already been considered the possibility of integrating them into the GIS architecture to help with hazard calculation (Lam and Swayne^). Nevertheless, although computerization can help handle the large amount of information needed, it can also lead to artificiality unless the ultimate goal pursued by the studies is clearly stated and the methodology to follow to achieve our objectives is detailed previously (Alexander*). For this reasons, due to the new working environment that the incorporation of GIS and physical models offer to volcanic risk assessment in comparison with conventional methods, the design and testing of a methodology, where the elements and procedures to be followed to produce the information required by the assessments were clearly identified, has become a primary step in order to achieve the improvement of the current production methods. 2.1 Methodological background Classical volcanic risk assessments have usually been forced to appeal to a variety of calculation methods that require to gather and analyse large amounts of data of diverse nature. Furthermore, the scarce data availability that usually characterises volcanic areas and the limited technical means that conventional methods

4 114 GIS Technologies and their Environmental Applications have at disposal to process these data, have in many cases led the studies to assume certain methodological simplifications that have ultimately hindered the achievement and completion of accurate risk assessments (G6mez-Fern3ndez & Arafia-Saavedra^). The lack of a widely accepted standard methodology to follow to carry out volcanic hazard and risk assessments has prevented us from having a development basis from which to select and adapt its most relevant features to the GIS working environment. For this reason, there has been the need to peer review the complete set of assessment methods followed by classical studies in order to identify the most significant elements required to carry out volcanic risk estimation and to devise a way to represent these elements into the GIS frame. The procedure followed to carry out these tasks has been based on the principles and techniques proposed by cartographic modelling methodologies (e.g. Tomlin*), which have given us the possibility of decomposing hierarchically the problem of risk assessment into each of its components. 2.2 Methodology design As afirststep in the development of the methodology, a detailed analysis of the factors and variables that play a major role in volcanic risk and the way they relate to each other has been required. The results obtained from this analysis have served us as the departing point from which the databases and the operations required to carry out the volcanic risk assessment in the frame of a GIS have been identified. The methodology designed makes use of a series of parameters called volcanological and environmental variables to identify the eruptive phenomena taken potentially place at a vent of our selection, together with their eruptive styles and the conditions existing for the dispersal of their products (G6mez-Fem&ndez*). This set of data provide the input parameters to the corresponding physical simulation models, which provide the way to calculate the distribution of the products of a certain phenomenon of our interest. The simulation process produces an hazard map called commonly risk scenario (figure 1), where the results of the calculation are usually represented in probabilistic terms. The analysis of the potential effects of the eruption simulated on the elements located in the area identified by the risk scenario constitutes the

5 GIS Technologies and their Environmental Applications 115 VOLCANOLOG1CAL VARIABLES ENVIRONMENTAL VARIABLES Potential Eruptive Styles Conditions for dispersal of the products PHYSICAL ERUPTION MODELS RISK SCENARIO POTENTIAL RISK Value of goods and properties Vulnerability SOCIO-ECONOMIC VARIABLES SUSCEPTIBILITY VARIABLES Figure 1. Schematical representation of the process designed to assess volcanic risk

6 116 GIS Technologies and their Environmental Applications last stage of the risk assessment process. To achieve this objective, information on the value of the goods, properties and population of the area affected and on the vulnerability of each of them against the phenomenon represented in the risk scenario must be acquired. This information is provided by means of a series of socio-economic variables. The results of confronting the scenario with the socio-economic variables provide information on the potential risk, understood as the measure of the value that can be lost or affected directly or indirectly as a consequence of a certain event. 2.3 Methodology application In order to check the design of the calculation structure developed, to test its efficiency and accuracy and to identify the main constraints faced when applied to an actual assessment, a pilot study at Tenerife island (Canary islands, Spain) has been carried out. The aim pursued by this analysis has been: (1) to assess the risk posed by lava flows proceeding from the occurrence of effusive eruptions occurring at several points of the island and, (2) to compare the potential distribution of the flows and the extent of damage produced depending on the location of the eruptive vents selected and the socio-economic characteristics of the areas affected (G6mez-Fern ndez*). With this purpose, the model developed has been implemented in a system where ILWIS has been used as the GIS software basis. Due to the fact that the study has been limited to the assessment of one eruptive phenomenon, only the databases and the physical model required to carry out lava flows risk analysis have been considered for inclusion in the system (figure 2). In the process of construction of the system, special emphasis has been given to the production of outputs in order to assure that the time, interpretability and accuracy constraints found by conventional methods could be solved. To provide comprehensible information regarding the results of the simulation and of the potential risk assessment process, the system implemented generates automatically for each event simulated a series of graphical and tabular outputs that provide information on: (1) the potential distribution of the lava flow paths identified by the model together with additional contextual information to aid interpretation, (2) the distribution and characteristics of each of the socio-economic variables located in the potential affected and buffer areas and an estimate of their potential losses and, (3) a synthetic potential risk map that

7 CIS Technologies and their Environmental Applications 117 SOCTOECONOMIC DATABASES POPULATION I ROAD NETWORK HYDRAULIC INFRASTRUCTURES LAND USES ENARIO V S ianalysis x IB o ^c i 03 & t I 3 H ^ Q 2 WA FLOW I 3 s x 0 SIMULATI * o OLCANOLOCICAJL DATABASJ ERUPTIVE STYLES t WATER INTERVENTION SUSCEPTIBILITY t i 1 DIGITAL ELEVATION MODEL 8 o

8 118 GIS Technologies and their Environmental Applications includes the information regarding the magnitude of the potential losses of each element affected by the flows and attached explanation tables (figure 2). 2.4 Methodology constraints and future developments The results provided by the application of the methodology have been discussed and analysed taking into account: (1) the conditions established for the implementation of the model, (2) the characteristics of the methodology devised to carry out volcanic risk assessment and, (3) the computer tools selected for its development (G6mez-Fern ndez*). This thorough analysis has provided us the way to identify the constraints that the method devised has found for the achievement of the objective pursued with the incorporation of GIS and physical models to the volcanic risk assessment calculation, i.e. the improvement of the methods to produce information. Basically the methodology devised has provided the way to surmount the time, interpretation and accuracy constraints faced by classical assessments, due to the sensible reduction achieved for the calculation times, the improvement on the quality of the outputs produced and the establishment of a clear identification of the variables and procedures that play a role in the risk assessment process. In spite of the substantial improvement that the methodology devised has signified in general terms, there are two features that need to be accounted for in future developments as they have been revealed as fundamental to give an operational character to the assessment method. First, there would be the need to consider a complete physical integration of the simulation models into the structure of the system as, at this phase of the study, its independence has slowed down the process of calculation, due to the need to create additional procedures to exchange data and parameters between them and the GIS. Furthermore, during the application of the system it has been stressed the need of an adequate user interface to provide communication between the user and the system. Without it, advanced technical skills to manage the tools used and the methodology devised are required, what makes it a technique difficult to access by inexperienced users. Therefore, the development of an operational and powerful information system will depend basically on the achievement to include these goals in its design.

9 GIS Technologies and their Environmental Applications Statement of the volcanic risk assessment information system development strategy The development of the methodology for volcanic risk assessment that has been presented through the previous section has provided us with an efficient solution to the performance constraints that classical studies used to find to produce volcanic hazard or risk maps. Moreover, this practice has allowed us (through the application of the methodology to a specific case study) to acquire a basic technical knowledge of the needs that a general user would expect from a system of these characteristics, speaking in terms of: (1) the way to communicate with the system and to require information from it, (2) the kind of information expected to obtain from the calculation processes and, (3) the way to display these results. At this point, the main aim to be achieved by future research work has passed to be the development of an information system capable of achieving the specific series of system requirements which can be extracted from the analysis of these needs. The adoption of this perspective can help us also to solve the troubles faced during the application of the methodology. To carry out this task, the assumption of an object oriented approach to develop the software has been considered the most efficient way to construct a solid system architecture. Nevertheless, due to the wide user community that can benefit from the such a system (civil defence officers, insurance companies, land use managers, etc.), all of them with a different scope of the information required from it, we have limited by the moment the scope of the application to the production of the information required to elaborate volcanic risk prevention and management plans. Acknowledgements The labour presented in this paper has been carried out,firstunder the auspices of the Teide Project: European Laboratory Volcano, funded by the Environment Programme of the EU-DG XII (Science, Research and Development) and, currently under a Marie Curie Research Training Grant, awarded by the same sources. Thanks are also due to the researchers involved in the Teide project, to the Cabildo Insular de Tenerife, the Institute Geogrdfico Nacional and to the local and national Protecci6n Civil services, either at its headquarters or their branches at the Canary Islands.

10 120 GIS Technologies and their Environmental Applications References [1] Foster, H.D., Disaster planning: the preservation of life and property, Springer, New York, [2] Gupta, R.R & Joshi, B.C., Landslide hazard zoning using the GIS approach - a case study from the Ramganga catchment, Himalayas. Engineering Geology, 28, pp [3] Alexander, D., Natural Disasters, UCL Press, [4] G6mez-Fern&idez, P., Desarrollo de una Metodologia para el Andlisis del Riesgo Volcdnico en el Marco de un Sistema de Informacion Geogrdfica, PhD Thesis (unpub.), Facultad de Ciencias Geol6gicas, Universidad Complutense de Madrid, [5]Pareschi, M.T. & Berstein, R., Modeling and image processing for visualization of volcanic mapping, IBM Journal of Research and Development, 33 (4), pp ,1989. [6]Lam, D.C.L. & Swayne, D..A., Integrating database, spreadsheet, graphics, GIS, statistics, simulation models and expert Systems: experiences with the Raison system on microcomputers. NATO ASI Series G26, pp , [7] G6mez-Ferndndez, F. & Arafia-Saavedra, V., Design and development of a GIS volcanic risk assessment methodology for the prevention, management and mitigation of volcanic crisis, Submitted. [8]Tomlin, C.D., Cartographic Modelling, Geographical Information Systems, eds. D.J. Maguire, M.F. Goodchild & D.W. Rhind, Vol. 1, pp , 1991.