Aqueduct country and river basin rankings
Gassert, F., P. Reig, T. Luo, and A. Maddocks. 2013. “Aqueduct country and river basin rankings: a weighted aggregation of spatially distinct hydrological indicators.” Working paper. Washington, DC: World Resources Institute, November 2013.
Drought severity measures the average length of drought times the dryness of the droughts from 1901 to 2008. Drought is defined as a contiguous period when soil moisture remains below the 20th percentile. Length is measured in month and dryness is the average number of percentage points by which soil moisture drops below the 20th percentile.
(0-1): Low (<20)
(1-2): Low to medium (20-30)
(2-3): Medium to high (30-40)
(3-4): High (40-50)
(4-5): Extremely high (>50)