Historic efficiency improvements would meet only a fraction of the projected gap

Projected Freshwater Supply Shortfall in 2030. 2030 Water Resources Group, 2009

Agricultural yields in both rain-fed and irrigated areas grew at an annual rate of about 1 percent between 1990 and 2004, a major driver of overall water productivity improvements. A similar rate of improvement occurred in industry. Were agriculture and industry to sustain this rate of improvement through 2030, it would address only 20 percent of the supply-demand gap, leaving a large deficit to be filled. Similarly, a business-as-usual supply build-out, assuming constraints in infrastructure rather than in the raw resource, will address only a further 20 percent of the gap. Even today, a gap between water demand and supply exists when some amount of supply that is currently “borrowed” from environmental requirements is excluded, or when supply is considered from the perspective of reliable rather than average availability.

The impacts of global climate change on local water availability, although largely outside the scope of this study, could exacerbate the problem in many countries. While such impacts are still uncertain at the level of an individual river basin for the relatively short time horizon of 2030, the uncertainty itself places more urgency on addressing the status quo challenge.

[Jim] Note that “Existing accessible, reliable supply” is taken to be constant to 2030. Color me skeptical.

Charting our water future: Economic frameworks to inform decision-making [pdf]

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