I just received a PR email from Veolia Water's publicity folks touting the release of a new report (although it is dated February 2013 - guess I am on the 'D-List' with Kathy Griffin) from the Columbia Water Center and Veolia, America's Water Risk: Water Stress and Climate Variability'.
I think some of the material from this report was presented here.
Here is an infographic:
From the infographic page at Growing Blue:
According to Upmanu Lall, the director of Columbia’s Water Center, many of the tools which are currently developed to help businesses assess water risk “actually understate the risk of climate variations.” Lall noted that in addition to water scarcity projections, certain areas should also consider their exposure to drought, since droughts will magnify any problems created by water scarcity.
In developing this study, Columbia researchers first developed a new water research metric that they call the Normalized Deficit Cumulated (NDC) index. The index pulls from more than 60 years of precipitation data and the current water use pattern for the United States in order to better depict the discrepancy between water use and availability.
The study clearly shows that decision-makers need to be thinking beyond the problems of water scarcity, to the way drought will affect regions that are already facing problems. Said Lall, “Droughts will create an additional impact that needs to be understood, because drought magnifies the effects of scarcity.”
Explanation of the Normalized Deficit Index (NDC)
Two risk metrics were developed to capture the influence of within year dry periods (Normalized Deficit Index – NDI) and of drought across years (Normalized Deficit Cumulated – NDC). The NDI is computed as one number for each year using historical daily rainfall data for the area and current daily water needs. It measures the maximum cumulated water shortage each year during the dry period that needs to be provided for from ground water or from surface water storage or transfers from other areas.
The NDC is computed as one number over the historical climate record. It represents the largest cumulative deficit between renewable supply and water use over the entire period. Consequently, it reflects the stress associated with multi-year and within-year drought impacts at a location. Given that 60 years of historical climate data were used, the maximum of the NDI (i.e. the worst single year), and the NDC (i.e., the effect of a string of bad years) may have an average recurrence interval of approximately 60 years. The NDI data provides insights into other recurrence intervals as well.