Calculation of specific assets

After evaluation of the asset values for each land use type a connection with the catchment area has to be made. This could be done using the method of regionalisation. This method to calculate the flood damage potential is composed of three steps:

  • determination of asset value per land use type in [] 
  • identification of corresponding land use areas in[m] 
  • intersection of statistical-economic data and land use types to calculate the specific asset value in [/m] 

The main advantage of this method is that no time-consuming mircoscale object orientated determination of asset values is used. This approach bases only on statistical governmental data as well as on the classification of different land use types. But, the calculated damages do not represent real damage. More detailed calculations are only feasible in case of micro scale investigations. Data collection in case of object related damage assessment is time-consuming. Nevertheless, this method is applied when it is necessary to assess the damage potential of objects like hospital, landmarks, and so on.

Method of Regionalisation

Using digital information (GIS) to identify the corresponding land use types the specific damage for each land use type can be calculated. Applying a Geographic Information System, it is possible to combine all necessary data for determination of damage potential like:

  • inundation areas with water depth
  • land use distribution
  • specific asset values
  • damage functions 

The key idea of the method is the conversion of all relevant information in raster data.

For the program run following equation can be considered:

On the basis of the damage functions the damage within each grid cell  can be calculated by the following equation:

with jiD, = specific damage for grid cell [i,j] in (/m), C percentage of damage in depend-ence of land use category Ln and the water depth h=Lnj,ii,j in grid cell [i,j] in [%] andLnV = specific as-set/capital stock for each land use type Ln in [/m].

Result of this damage assessment in a raster in which for each cell the specific damage in /m is calculated. Total damage for a flood event can be determined by summarising the values for each cell and multiplying with the affected area. The annual damage [/m/a] can be evaluated also for each cell of the raster.

The result of such a grid cell oriented damage calculation is demonstrated inthe figure on the left. It shows the spatial distribution of specific damage for a certain flood event and a given region affected by flood. Multiplying this specific damage with the area of the grid cell and adding up this value for all grid cells gives the total damage for this area and flood event.

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