Water Resources of the United States: Agricultural and Environmental Issues

Introduction

• Water resources are valuable for human use including agriculture, industrial, household, recreational, and environmental activities.
• Only 2.5% of Earth's water is freshwater, with over two-thirds frozen in glaciers and polar ice caps.
• Global water demand exceeds supply, with 70% of water used for agriculture.
• Environmental change is impacting water resources due to the climate and hydrologic cycle.
• Increasing human population is leading to competition for water, resulting in the depletion of significant aquifers.

Water Resources and Geographical Context

• The U.S. has abundant water resources, with 4.5% of the world's population and nearly 8% of its freshwater resources.
• The Great Lakes contain six quadrillion gallons of water.
• The Mississippi River provides water to around 15 million people.

Factors Affecting Water Resources

• Population growth, especially in water-short regions.
• Urban migration increases water demand.
• The need for food security and better living standards.
• Competition between different uses of water resources.
• Pollution from factories, cities, and farmlands.

Availability of Water

• Water is a renewable resource but limited in availability per unit of time in any region.
• Most continents have an average precipitation of about 700 mm annually.
• Africa remains relatively dry despite 640 mm annual precipitation due to high evaporation rates.
• Water scarcity is significant in regions with less than 500 mm annual rainfall, affecting crop yields.

Groundwater Resources

• Around 30% of Earth's freshwater is stored as groundwater.
• Groundwater recharge is slow, with a typical rate of 0.1% to 3% annually.
• Groundwater provides 23% of global water usage.
• Overdraft of groundwater is a major issue, with withdrawals exceeding recharge rates.

Stored Water Resources

• Many U.S. dams were constructed in the 20th century to increase water availability.
• Sedimentation reduces dam capacity by an estimated 1% annually.

Water Use and Consumption

• U.S. freshwater withdrawals total around 1600 billion liters daily.
• 80% of water is sourced from surface waters, 20% from groundwater.
• Worldwide, 70% of withdrawn water is consumed and nonrecoverable.

Agriculture and Water

• Plants require water for photosynthesis, growth, and reproduction.
• Water use for different crops varies significantly.
• Irrigated crops require significant water but account for 40% of global food production.
• Energy costs for irrigation are high, affecting the economics of irrigated crops.

Soil Salinization and Waterlogging

• Salinization is a major issue with irrigation, concentrating salts in soil and affecting crop growth.
• Waterlogging impairs crop growth due to water accumulation in soil.

Water Contamination and Human Diseases

• 20% of the global population lacks safe drinking water.
• Untreated sewage is a major contamination source, leading to waterborne diseases.
• In the U.S., 40% of freshwater is unfit for drinking due to contamination.

Conflicts Over Water Use

• Increased freshwater withdrawals lead to conflicts within and between countries.
• 263 transboundary river basins share water resources internationally.

Using Water Wisely

• Agriculture should be the primary focus for water conservation incentives.
• Implementation of water-saving practices like drip irrigation is recommended.
• Governments need to control water pollution and manage water resources sustainably.

Additional Topics

• Related articles on water conservation, water cycle, emergency preparedness, and more.