Measuring water security with hydro-economic classification

The IIASA-developed hydro-economic classification evaluates watersheds, countries, or regions using a combination of hydrological complexity and economic-institutional coping capacity [1]. In this way, it can identify vulnerable regions where the prevailing hydro-climatic conditions for human water use are complex and economic-institutional coping capacity is low.

Hydrological complexity is defined on the basis of four indicators:

• A measure of water availability, defined as total renewable water resources per capita
• A measure of the relative intensity of water use, defined as the ratio of annual water withdrawal for agriculture, industry, and the domestic sector to the total renewable water resources
• The runoff variability, defined as the variation in monthly runoff for a 30-year period showing both inter- and intra-annual variability
• A measure of the dependency on external water resources, defined as the ratio of external (i.e. from outside national boundaries) water resources to total renewable water resources.

All four indicators were compiled based on data and model calculations consistent with the Representative Concentration Pathways (four greenhouse gas concentration trajectories), and the Shared Socioeconomic Pathways (five possible paths human societies could follow over the next century), which together provide the foundation for global climate modeling.

For economic-institutional coping capacity, researchers selected GDP per capita as a measure of economic strength and financial resources available for investing in risk reduction and adaptation. Although there are some exceptions, GDP per capita can also often provide a proxy for the availability and efficiency of institutions to cope with complex hydrological conditions.