Reducing water scarcity by improving water productivity in the United States
Water is a scarce resource utilized by farmers, cities and industries to advance their economic activity. As population increases and the effect of climate change intensifies, competition among multiple stakeholders will exert additional pressure on already over exploited resources. According to the US Government Accountability Office, four out of five states in the United States will face water scarcity somewhere in their state in the coming decade.
Historically, water scarcity has been managed by focusing on supply augmentation; either by storing excess water in reservoirs through construction of dams or by diverting water from regions with excess water to regions with water scarcity. In addition to the high infrastructure cost of building dams, they disrupt river ecology. Additionally, as dams age, there is an increased risk of failure and additional costs associated with dam removal. Even more concerning is the possibility that there may not be enough water to satisfy the demands of all users. As an example, the Colorado River Basin does not have enough water to meet the demands of all its users. The water levels in Lake Mead and Lake Powell, the two largest artificial reservoirs in the United States in terms of water capacity, have remained far below the maximum level due to a decreasing supply of rainwater and snowmelt and increasing demands. This has motivated many water researchers and practitioners to focus on demand management to tackle water scarcity.
To reduce the demand, we must understand the spectrum of water usage for different activities. My research as a civil engineering student in the lab of Dr. Landon Marston at Virginia Tech focuses on understanding water usage by agricultural crops in the United States, with the goal of reducing water usage. One of the strategies of reducing demand is “benchmarking”, where similar water users are grouped together and target benchmarks of productivity are set for each group by choosing the productivity of better than average performers. In the case of water usage, a better than average performer would utilize less water than others within their group. To ensure fair comparison, water users with similar environmental and technological profiles are compared.
What if all water users adjusted their water productivity to match their industry benchmark level? How much water would be saved and where? With the assumption that water users with similar environmental and/or technological profiles have the potential for similar levels of water productivity, we established water productivity benchmark levels for the median (50th percentile), top quarter (25th percentile) and top decile (10th percentile) of water users within each industry and for each crop. A benchmark level at 50th percentile means that all water users whose water productivity is lower than 50% of similar water users improve their water productivity to the 50th percentile. Improving water productivity has the potential to save water without reducing economic activity. We incorporated water savings into a national hydrological model (WaSSI) and found that streamflow depletion can be reduced on average by about 6 percent by moving unproductive water users to the median water productivity within their industry and streamflow depletion can be reduced by 23 percent if unproductive water users adjust their water productivity to match the top decile of water users within their industry.
One of the limitations of benchmarking techniques is that it does not consider the economic or technical feasibility of shifting water users with low water productivity to higher water productivity. It simply demonstrates the existence of highly productive water users and points to a range of options that a user might select from. Rather than prescribing a solution, it assumes that each water user is better suited to make that decision. Additionally, water savings resulting from improved productivity do not necessarily translate into actual savings. In some cases, the saved water is utilized by the water user to further advance their economic activity. For instance, a farmer might use their water ‘savings to grow more water intensive crops or increase cultivated area. Nevertheless, the benchmarking technique allows us to estimate the upper limit of water savings that can be realistically achieved by comparing water users in the same industry.