A system for supporting decisions in emergency situations
1. IntroductionTaking of correct decisions in the emergency situations, such as flood or spilling of dangerous chemicals may save human life and property. Taking of such decisions occurs under severe stress. Decisions have to be taken quickly, and the potential mistakes may have catastrophic consequences. That is why it is essential to prepare beforehand the principles of proceeding for the cases of all the potential threats in order to be able to properly react in every such situation. It is necessary to train future decision makers, so as to provide them with knowledge on the ways of reacting to hazards. It is necessary to carry out preparatory analyses and prepare for reaction to threats, due account being taken of the technical and financial possibilities.
Earlier preparations are often neglected, because they require bearing some cost. Yet, this cost is incomparable with the losses that can arise by neglecting the preparations.
The ProDec (Procedures for Decisions) software has been elaborated within the framework of the TRANSCAT Project, whose purpose is to develop the system for supporting decisions in transboundary catchment management.
2. The principles of functioning of the ProDec system
The ProDec system makes use of simple decision rules of the following
If a definite threat takes place
then undertake a definite action
The states of threat or hazard are recognised on the basis of the current values of the observed indicators. In order to state whether an emergency state actually takes place, we have to check whether the indicator values are contained in definite intervals. So, on the basis of known values of indicators we check what kinds or degrees of threats may occur, and then, by applying the decision rules we determine the list of actions corresponding to these kinds or degrees, i.e. to the state identified.
The novelty in the ProDec system is constituted by the use of fuzzy logic to define the decision rules, and more precisely - to define the degrees or states of threat or emergency on the basis of the indicators observed. The precise intervals of vlues, which define the degree of emergency, have been replaced by the intervals with fuzzy borders.
Fig.1 Example of definition of verbally designated water level "states" with the use of "fuzzy" interval of values (in red: the ranges of values corresponding most to a given verbal designation).
By employing fuzzy logic we gain additional information in doubtful situations, especially when th current values of the indicators are close to the limits of the intervals indicating a proper emergency state. We obtain, as the result of application of the fuzzy decision rules, the list of actions together with their degrees of belongingness to the set of actions to be actually implemented. If the degree of belongingness or membership in this set is equal 1, then this action should unconditionally be carried out. The closer the membership degree to 1, the stronger the indication to implement a given action. The closer the membership degree to 0, the lesser the need for carrying out a given action.
The present description of the ProDec system and its use refers to the application for water-related emergencies and actions, but of course, the system can be used in any appropriate context.
3. The structure of the ProDec system
The ProDec system is composed of two parts:
In the first part the set of decision rules is prepared. On the basis of the measured or forecasted values of indicators, like, e.g. water level or forecasted precipitation, the rules determine whether emergency situation would arise. For various degrees of emergency and kinds of states the rules determine the actions to be undertaken. So, for instance, in case of the threat of local flooding assistance ought to be secured in salvaging of property, while in case of indication of a large flood it will be necessary to carry out quick evacuation of the population.
The second part functions on the basis of the set of decision rules prepared with the use of the ProDec's first part. Knowing the current values of the indicators used to determine the degree of emergency, we apply these the decision rules, and obtain the set of suggested actions, to be undertaken (or considered) in a given situation.
4. The stages of development of the ProDec decision system
Preparation of the decision support system, whose functioning is based upon the decision rules, can be divided into the stages specified below. These stages are listed here in the sequence of their execution, but in the course of work there may arise the need of complementing and adding precision to the information prepared in an earlier stage.
4.1 Determination of the threats and actions
The very first step in the elaboration of decision rules is to establish the list of all the possible threats and degrees of emergency, as well as actions, which might be undertaken in oder to deal with the theats. It is important to give the threats and actions short names, but at the same time unambiguously, because these names will be used in the definition of the decision rules. If we envisage undertaking of different actions depending upon various degrees of emergency, we should treat these degrees as different "kinds of threat".
An example of threats that can be defined for a river valley is as follows:
And the examples of actions:
4.2 Division into subareas
In order to correctly elaborate the decision rules we must divide the area under threat into the subareas featuring similar degrees and character of hazard. In case of floods this division results mostly from terrain relief, but it may also be associated with the nature of land use, administrative breakdown, etc.
A too detailed division requires definition of a high number of decision rules, and so we should distinguish only such subareas, over which the hazards are clearly different, and the ones, which require different actions in the case of emergency. Thus, for instance, we can distiguish the areas situated close to the river channel within the floodplain, which are often flooded, and the areas, which are flooded only sporadically. On the op of this, we can determine the urban areas in view of the necessity of taking additional actions.
4.3 The choice of measured quantities
Rational decisions can be taken only on the basis of available information. When designing a decision making supporting system we have to make choice of the quantities, that will constitute the basis for decision taking. Obviously, information on these quantities has to be always available and up to date, since otherwise our decisions risk to be completely erroneous. While defining the decision rules, we will often perceive the need of organising or complementing the system of monitoring the emergency situations, which would regularly provide information needed for decisin taking.
For purposes of determination of the degree of flood threat over a given area we can use the measurements of water level and flow upstream from the area, as well as the current forecasts of precipitation.
4.4 Definition of the degrees of emergency
In order to conclude whether we actually deal with flood emergency we have to know the current values of the indicators selected in the preceding step as the basis for taking of decisions. Depending upon the locations of values of these indicators in terms of appropriate value intervals we will conclude whether we deal with actual emergency or not. In the ProDec system we assign the ranges of indicator values telling names (like, e.g., high level, normal level, low level, alarm level, etc.), and the emergency state is defined with a simple and legible logical expression.
Fig. 3. Definition of the emergency state on the basis of known values of indicators (water level, precipitation forecast) by specification of the expression using the names of "fuzzy" intervals of values of theseindicators, such as Low, Normal, High, Emergency.
4.5 Formation and testing of decision rules
A decision rule is an assignment of action to the values of variables (indicators), here: defining the emergency state. Every degree or kind of emergency can be ascribed many actions, which should be undertaken after the respective emergency state had been identified on the basis of surrent values of the observed indicators.
Fig. 4. Decision rules
In the above example of the decision rules the state
"Flood alarm for the town of Głuchołazy"
has been ascribed the actions:
"Strengthening flood protection walls" and
"Announcement of flood alarm".
The state called "Flood alarm for the town of Głuchołazy" was defined beforehand through a logical expression, in which definite intervals of the masured indicators appear through appropriate names. If for the curent values of these indicators the logical expression is "true" (conditions are fulfilled) then the actions ascribed this state ought to be undertaken.
Since the conditions used in decision rules may be complicated, it is necessary to check, whether they indicate the actions conform to our knowledge and expectations. The ProDec system enables precise testing of the rules defined. Testing consists in preparation of a number of data sets corresponding to various situations and running the rules for these data.
Fig. 5. The set of tests and the values of indicators for the test called "High wate level, medium precipitation".
For the selected test ProDec verifies the decision rules for the provided values of indicators and shows the results indicating the actions to be undertaken. In case of the here illustrated test data the result points out the following actions:
Fig. 6. The result of the test run
For purposes of testing we can obtain a more detailed information, showing how the final result was generated:
Fig. 7. Detailed output from the test run of the decision rules.
The rows with the question marks correspond to the verified conditions (states). Number 0 against the grey background in the rows of this type means that upon the verification of conditions we have concluded that this state does not take place and none of the corresponding actions must be undertaken. The number 34 against the grey background in the row suggesting "Strengthening of the flood protection walls" defines the degree of membership of the respective set of data to the state "Threat downstream of Głuchołazy" on the scale between 0 and 100, meaning that the suggestion of carrying out this action is rather weak. If this value were 85 we could speak of a strong suggestion, and for 100 - of an absolute necessity of executing this action.
4.6 Detailed description of the actions
The final stage of preparation of the ProDec system to practical use is elaboration of the detailed descriptions of all the actions included. These descriptions ought to contain the following information:
Preparation of this information in the electronic form (possibly as web pages in HTML language) offers additional advantages. This information can then be easily accessed, found and updated.
The ProDec system facilitates elaboration of these descriptions by making available a simple editor of the WWW pages, with which legible pages can be created containing maps, figures, etc., without knowledge of the HTML language.
4.7 Installing the system
Upon the elaboration of the system with the help of the ProDec software supporting definition of the decision rules we obtain as the output a file containing the definitions of the decision rules (in the XML format) and a number of auxiliary files (in the HTML format), such as descriptions of actions, information on indicators, etc. Installation of the system reduces to the transfer of all these files over to the server, along with the software files for decision support (developed in the PHP technology), a standard component of the TRANSCAT TDSS system.
4.8 Final testing
After having installed the system we have to carry out the final tests, during which functioning of the system, completeness of information, and simplicity of use will be checked. For purposes of testing we can change the values of the indicators measured, appearing in the decision rules in order to analyse the reaction of the system to various scenarios.
Testing should be performed by the future users of the system or specially appointed teams. Testing should not be carried out by the developers of the system, since knowing well the functioning of the system they are much less likely to encounter the difficulties, which a user can run into, and which ought to be properly dealt with so as to make the system fully usable.
5. Using the results of modelling
When defining the decision rules in the ProDec system we make use first of all of the experience and knowledge of the persons dealing with a particular problem, here flood protection, on the given area. Knowing the current values of water levels and flows as well as precipitation forecasts we can determine the degree of threat and the necessary actions. This is altogether not an easy task, for the interrelatins between the indicators may be highly complex.
In order to elaborate the proper decision rules for flood hazard it is possible and advisable to use the models of surface water flow. These models use information on land relief and cover on the areas threatened with potential floods. Having similar current data as in the decision rules mentioned we can also apply models so as to predict the areas flooded and the potential destructions. Modelling allows for the complementing of knowledge neded to establish the decision rules.
Another solution consists in the direct use of modelling in the decision process. In this case the current values of the indicators are introduced as the input data of models and the output from models is used in the form of definite indicators in the decision rules.
6. Concluding remarks
The use of the modern techniques of fuzzy logic in the ProDec system alows for the formulation of the decision rules as legible phrases similar to those of the natural language. Owing to this it is easier to understand and analyse the principles of decision taking and improve the rules adopted.
No doubt elaboration of the decision rules constitutes a substantial effort. Yet, even undertaking of such effort can pay back by itself. Frequently during analysis various shortcomings are uncovered and proposals of new solutions emerge.
It is important to secure participation of several persons in the process of elaboration of decision rules in order to be able to confront various opinions and asessments concerning the evaluation of hazards and the best counteractions. Writing down the decision rules in a formalised manner and elaboration of the complementary documentation in the form of files accessible through internet facilitates communication and identification of various kinds of gaps and errors in the preparations.
ProDec - procedures
for decision making (editor & tester)
Developed in the framwork of TransCat project
Contact: Andrzej Ziolkowski