Scenario - Based Prediction of U.S. Water Withdrawal and Consumptive Water Use

<p>U.S. water withdrawals have increased slowly since 1980, despite significant growth in the population and economy during this period. This implies that other factors have contributed to offsetting decreases in water withdrawals. The economic input-output life cycle assessment (EIO-LCA) model was used to estimate the total water withdrawal for 135 industrial summary sectors for 1997 and 2002. The change in water withdrawals for the economy from 1997 to 2002 was allocated to changes in five governing factors — population, GDP per capita, water use intensity, production structure, and consumption pattern — using structural decomposition analysis (SDA). The changes in population, GDP per capita and water use intensity increased total water withdrawal, while the changes in production structure and consumption pattern decreased water withdrawals from 1997 to 2002. Consumption pattern change was the largest net contributor to the change in water withdrawals. The counter balancing of these factors is what has kept U.S. water withdrawals relatively constant. To project U.S. water withdrawal for the next 20 years, four scenarios were developed for each of the five governing factors based upon available predictions or historical trends. The total water withdrawals for U.S. 66 aggregated industrial sectors for 2013-2030 were projected using the EIO-LCA model with fixed and changing economic structure, respectively. The structure and consumption pattern were held constant at the 2012 level and the other three factors were varied across time in the EIO-LCA model with fixed economic structure, while all five governing factors were changed across time with changing economic structure. The maximum projected total water withdrawal is 370 trillion gallons for 2030, which is more than 2.5 times the 2005 U.S. water withdrawal, corresponding to a scenario with maximum growth assumptions for all factors considered. The medians of total water withdrawals projected by the models with constant vs. evolving economic structure for 2013-2030 follow a continuous increasing trend, and the projected median values by the two models are comparable. The median of total water withdrawal will reach around 180 trillion gallons in 2030, about 1.2 times the 2005 U.S. water withdrawal. The variance in GDP per capita and water use intensity were the two most significant contributors to the uncertainty in projected total water withdrawals for U.S. industrial sectors. The distinction of consumptive and non-consumptive water use is important for water resource management and assessment of availability and quality of water sources. Consumptive water use coefficients (ratio of consumptive water use to water withdrawal) were estimated by aggregated industrial sectors based on available data. The projected total consumptive water uses for all industrial sectors range from 45-47 trillion gallons in 2013 to 23-51 trillion gallons in 2030 using the EIO-LCA model with fixed economic structure. The median total consumptive water use is projected to grow at an average annual rate of 0.5% during this period. The effects of changes in cooling technology for thermoelectric power generation and irrigation technology for agriculture on changes in consumptive water use for other sectors during 2013-2030 were investigated. Changes in cooling technology do not impact consumptive water use projections for most sectors, but do impact power generation-related sectors. Shifts in irrigation technology do not only affect consumptive water use for agriculture, but also affect significantly the consumptive water use for sectors requiring agricultural products as important supply chain components.