As droughts rage and aquifers dwindle, people may wonder: Is there enough water to meet all our needs? Landsat satellites are helping to answer that question.
Water is one of the most important natural resources, one that’s long been considered inexhaustible. Yet changes in land use, climate, and population demographics are placing unprecedented demands on America’s water supplies.
Water Use Mapping
Using Landsat satellite data, scientists with the U.S. Geological Survey (USGS) have helped to refine a technique called evapotranspiration (ET) water-use mapping to measure how much water crops are using across landscapes and through time. These ET water-use maps are created using a computer model that integrates Landsat and weather data.
(This pair of ET water-use maps shows crop water use in California’s San Joaquin Valley in 1990 (left) and 2014 (right). Comparing the maps reveals changes in irrigation patterns during this period. Notice, for example, that water use intensified in many places (increase in blue areas) and some irrigated lands (green in 1990) transitioned out of agricultural production (reddish brown) by 2014.)
Crucial to the process is Landsat’s thermal (infrared) band. Thanks to that thermal band with its 100-meter resolution, water-use maps can be created at a scale detailed enough to show how much water crops are using at the level of individual fields anywhere in the country.
How Water-Use Maps Help
USGS scientists can map water use at different scales to address different water resource questions and concerns. Field-scale maps, for example, are powerful tools for estimating and managing water consumption on irrigated croplands. They can help answer questions such as:
- Where is water being used, how much, and by whom?
- Which types of crops are using the most, or least, water?
- Can water be used more efficiently without impacting crop yields?
Planning Today for Water Tomorrow
According to a recent Government Accountability Office report, 40 of 50 state water managers expect water shortages in their states between now and 2023. Addressing concerns about America’s water resources begins with a clearer understanding of water availability and water-use trends. Mapping water use based on Landsat satellite data has demonstrated immense potential at local and regional scales, and will soon become the basis for monitoring and assessing water use across the nation.