A Damage and Loss Assessment (DaLA) is usually created after a disaster. The standard DaLA methodology was developed by the UN Economic Commission for Latin America and the Caribbean (UN-ECLAC) in 1972, and has evolved with various international organisations since. Simply, it is a methodology for approximating damage and losses due to a disaster, basing calculations on a country’s economy and individual livelihoods to define the needs for recovery and reconstruction.
A Damage and Loss Assessment includes the following:
In this module we will learn how to calculate some of the basic data used in a DaLA, and use various QGIS functions to design a thematic map that shows damage and loss.
The BPBD has created a guide for damage and loss assessment for Indonesia, which defines varying degrees of damage and the economic impact of individual elements. Parts of this definition are shown here:
Notice that there are several elements at work here. First, damage to different types of infrastructure is “valued” differently. To put losses into monetary terms, the loss of a bridge has a loss value as does the loss of a public building or a private home. Then, depending on whether a feature suffers heavy, medium or low damage, a multiplier is applied to determine the value of the loss.
By adding up all of the damage it is possible to assess the total damages caused by a disaster. In the remainder of this module, we will calculate the value of the losses in our Sirahan project, and see how we can display them graphically using our map, based on the damage suffered in each hamlet.
We will create a damage and loss assessment map using our data from Sirahan village that we have been working with throughout this unit.
We will assume that all the buildings in the area_terdampak_Sirahan layer (hazard zone) suffered heavy damage from the disaster. Let’s create a spatial query to filter out these buildings.
We now have a group of buildings selected which we are assuming will suffer heavy damages. According to the BNPB Guide, we can assess the loss of heavily damaged buildings at a rate of 1.8 million Rp. per square metre, and the multiplier factor is 70%. Our formula for calculating losses is:
Total Building area x Loss Value per m² x Multiplier factor
Therefore we want to calculate:
Total Building Area x 1.8 million Rp. x 70%
in order to get a calculation of the value of total losses.
We will use the Intersect Geoprocessing tool, so that we can combine attributes from our district layer with the selection of buildings we have just made.
We will be using a QGIS plugin called Group Stats in order to calculate damages by each hamlet within Sirahan. You must be connected to the internet to install this plugin.
The Group Stats window will appear.
We’ve calculated the damaged area and we’ve created a table with damage data for various hamlets in Sirahan. Now let’s implement our losses formula in the same way.
“Damage” * 1800000 * 0.7
Your new column is now filled with information calculated from this formula, which assesses the value of losses in Rp for each individual building.
Now let’s calculate losses per hamlet using the Group Stats again.
Now we will join the tables that we created to our Batas_Desa_Sirahan attribute table and then use them to add new columns to the file.
- Join layer: BNG_Damages
- Join field: Nama_Dusun
- Target field: Nama_Dusun
- Join layer : BNG_Losses
- Join field: Nama_Dusun
- Target field : Nama_Dusun
We will conclude by representing these damage and loss values as a chart in QGIS.
The resulting map will look like this:
The size of each bubble represents the loss values in each hamlet. The bigger the size, the heavier the losses. Creating a map with this sort of chart can be an effective way to communicate the impact of a disaster. Now you can lay out your map, and then create another map showing Losses.