Bio-physical vulnerability can be well understood in GIS framework by considering contributing factors like soil type, slope, geomorphology, size of sub-watersheds and runoff at outlets, drainage pattern, land use/land cover, aquifer etc etc. In GIS by assigning weightage to each factors, weighted overlay analysis gives a composite scenario of the study area which can be further reclassified as high, medium and low flood zone. On the other side in case of social vulnerability how it can be workout at census village level by considering about 15 relevant social indicators? Finally social vulnerability map can be superimposed to corresponding physical vulnerability level i.e high, medium and low to achieve whole vulnerability.
What I gather from your post is that you are clear what you have to do. The only point about which you want to know about social vulnerability. There are possible two methods: typological and single index. In the typological approach you divide each of fifteen criteria of social vulnerability using the same method as you have applied in flood intensity zoning or standard deviation method wherein adding and subtracting half of the standard deviation to men you will get medium class and above the upper limit will be high class and vice versa. In this way by superimposing 15 maps you will get a typological map of regions at different level of social vulnerability and then by superimposing this map on physical vulnerability map you will have a detailed picture of cause, intensity and types of social vulnerability. In the case of sing index of social vulnerability case you make construct a composite index. In order to avoid negative values, from all the values of fifteen variables should be subtracted the minimum values of the respective variables and divided by the respective range e.g., x1-x1min/ximax-x1min. It will render all the variables to addition as they will become scale free. By adding all the variables variable-wise you will get final composite index. Choosing a method classification, divide this index into three classes of high, medium and low social vulnerability and again super impose on the map of physical vulnerability. In this method, there will be information loss and you will have no idea which of the social aspect will be most or least affected where. Good Luck.
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Thanks Mohammad Firoz Khan Sir for your valuable and an appropriate answer. let me try to get composite index as you suggested.
There are also many parameters drainage basins, which even can tell the arrival times of flooding from parts of the basin, to a point could be the event of flooding versus settlers in risk areas or zones interaction.
Many of these mathematical methods were proposed by Horton from you 50s of last century and his group, other something after a big advantage of these were developed, is that you can compare several basins in the same region.
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