TECHNICAL REPORT - The Water Cycle and the Economy - March 2023

6 THE WATER CYCLE AND THE ECONOMY | 1 This technical note provides details of the calculations and data sources in relation to Figure 2.2, ‘‘The water cycle, global water consumption by sector and blue water consumption exceedance’’, within “The What, Why and How of the World Water Crisis’ Review and Findings of the Global Commission on the Economics of Water” review prepared for the UN 2023 Water. [...] Minimum If we use the lowest estimate of global groundwater depletion of 84 km3/year (after Scanlon et al., 2023) and use the lowest estimate of blue water consumption in irrigation (after Rosa et al., 2020) of 1,083 km3/year or 77 km3/year, we obtain a lower bound estimate of unsus- tainable (exceedance of the sustainable limit) global blue consumption of 161 km3/ year. [...] Maximum If we use the highest estimate of global groundwater depletion of 304 km3/year (after Wada and Bierkens, 2014) and use the highest estimate of blue water consumption in irrigation of 1,550 km3/year (after Molden, 2007: 6) we obtain an upper bound estimate of unsustain- able (exceedance of the sustainable limit) global blue consumption of 414 km3/year. [...] Their estimate of global water exceedance is total blue water consumption estimated at 4,370 km3/year (3,563 km3/year for agriculture and 807 km3/year for other water consumption) LESS the estimated blue water planetary boundary of Steffen et al. [...] THE WATER CYCLE AND THE ECONOMY | 5 Hoekstra and Mekonnen (2012: 3234) estimated for 1996-2005 total (blue and green) water consumption of 9,087 km3/year, of which 6,684 km3/year is green water and 2,403 km3/year is blue water (which includes 1,378 for grey water).