The indicators used to calculate the GAIN Index are based on vulnerability and readiness aggregations down to the raw data themselves. An explanation of the methods used to convert the raw data into the scores can be found on this part of the GAIN website.
The map on the website of the index will give you an interesting 15-years-overview of the World’s vulnerability to climate-change.
You will find more informations here.
(Screenshot from http://index.gain.org/)