Battling Drought: The Science of Water Management

Despite nearly 200,000 square miles of reservoirs to store more than 1,400 cubic miles of water—a

globe. A planetary boundary for freshwater resources needs to secure water flows to regenerate precipitation, support terrestrial ecosystem functioning and services (such as carbon sequestration, biomass growth, food production, and biological diversity), and also ensure the availability of water for aquatic ecosystems.

Each year, the global water cycle delivers 110,000 cubic kilometers of water over land in the form of rain, sleet, and snow. (These values are approximate; various models have produced different estimates.) About 64 percent of that precipitation returns to the atmosphere through evaporation or transpiration (the use of water by plants, crops, grass