PNNL

Abstract

This paper establishes three future projections of global municipal water use to the end of the 21st century: A reference business-as usual (BAU) scenario, a High Technological Improvement (High Tech) scenario and a Low Technological Improvement (Low Tech) scenario. A global municipal water demand model is constructed using global water use statistics at the country-scale, calibrated to the base year of 2005, and simulated to the end of the 21st century. Since the constructed water demand model hinges on socioeconomic variables (population, income), water price, and end-use technology and efficiency improvement rates, projections of those input variables are adopted to characterize the uncertainty in future water demand estimates. The water demand model is linked to the Global Change Assessment Model (GCAM), a global change integrated assessment model. Under the reference scenario, the global total water withdrawal increases from 466 km3/year in 2005 to 941 km3/year in 2100,while withdrawals in the high and low tech scenarios are 321 km3/ year and 2000 km3/ year, respectively. This wide range (321-2000 km3/ year) indicates the level of uncertainty associated with such projections. The simulated global municipal demand projections are most sensitive to population and income projections, then to end-use technology and efficiency projections, and finally to water price. Thus, using water price alone as a policy measure to reduce municipal water use may substantiate the share of municipal water price of people’s annual incomes.