Advancing Water Security and Environmental Sustainability Through Evaluation of Water Use From the Field to State-Wide Scale

The United States (US) has experienced a surge in water shortages and droughts in recent times. Water shortages can result from population growth, climate change, inadequate water management policies, and the improper use of available technologies. The existing data and research on water use associated with water management policy structures are limited. Many states in the US follow strict regulations on water discharge into streams to enforce water quality standards; however, water withdrawal restrictions from streams are limited and inadequate in terms of water management at times of low flow. In states such as Virginia (VA), the Virginia Department of Environmental Quality (VDEQ) requires a Virginia Water Protection (VWP) permit for all water withdrawals from VA's surface waters. However, under certain provisions of VWP regulations, users are exempted from having a permit. Such permit exemptions exist in many states and present a severe challenge to water supply management. Chapter 2 compares the impact of permit exemptions on surface water availability and drought flows and compares these impacts to the relatively well-studied risks presented by dry climate change and demand growth in Virginia (VA). It was observed that in some regions, the impacts under the exempt user scenario were higher than those under the dry climate change scenario. In addition, water supply managers and government agencies use user-reported water withdrawal data to develop water management programs. Irrigated agriculture is the largest source of water consumption in the US. However, water-reporting regulations exempt users from withdrawing water for irrigation under a certain threshold. Moreover, as water is not metered, users often do not report their irrigation water use, resulting in considerable uncertainty about the impacts of irrigation withdrawals, which could potentially impact other water users, lead to water shortages or conflicts, and negatively impact stream ecology. Chapter 3 focuses on developing a novel methodology for quantifying unreported irrigation water withdrawals using publicly available USDA-Census and USDA-IWMS datasets. This method was used to evaluate the unreported water withdrawals in the VA. Finally, water use practices at the field level intersect with other environmental issues at a larger scale. For example, irrigation practices can influence nutrient uptake and transport at the field level. Insufficient water for irrigation, especially during critical growth stages, results in yield and economic losses and reduces agricultural productivity. However, excessive irrigation can lead to wasted water and energy as well as runoff and leaching of nutrients and agricultural chemicals. Therefore, the adoption of technological advancements at the field scale can reduce the amount of water needed to fulfill the needs while mitigating any nutrient impacts on the soil due to the excessive use of water. This is highly important when fertilizer prices are always high. Chapter 4 focuses on quantifying the impact of the use of short-term weather forecast data in irrigation scheduling on nutrient and water use efficiency in humid climates: experimental results for corn and cotton. It was found that irrigation scheduling using short-term weather forecast data is helpful for improving the nutrient and water use efficiency of corn. For cotton, nutrient and water use efficiency are highly influenced by irrigation and precipitation with respect to the growth stage.