April 1, 2006 Using census data, satellite images, aerial photographs, and computer simulations, a NASA scientist estimated that turf grass is the single-largest irrigated crop in the United States, three times more than corn. Experts say the environmental benefits of lawns' carbon dioxide intake are not enough to offset the impact of water usage.
MOFFETT FIELD, Calif.--Many Americans spend a fortune trying to maintain a healthy lawn. But one scientist says it's more important to help conserve the water supply than to keep grass green year round.
Growing up in Italy, Cristina Milesi never enjoyed a green lawn since yard space there is a luxury. So, when the NASA scientist moved to Montana, she was shocked by what people do for a luscious lawn.
Cristina Milesi, a remote-sensing scientist at California State University-Monterey Bay and at NASA/Ames Research Center in Moffett Field, Calif., says, "I would see all the sprinklers starting every evening punctually and watering half of the driveway, half of the walkway, and then a little bit on this lawn."
Lawns are the single-largest irrigated crop in the United States, three-times more than corn. Milesi cringed at the waste of such a precious resource. So, she used census data, satellite images, and aerial photographs to estimate how much turf grass was in the 48 contiguous states. Then, she applied a computer simulation that revealed the environmental impact based on care of the grass.
"We really undervalue water as a resource,ý Milesi says. What she found was surprising. While lush lawns take in lots of water, they also take in carbon dioxide. Experts, however, say this is not enough of a benefit to keep a beautiful lawn. Conservation is now mandatory in some cities, and homeowners are even paid to switch to native plants and grasses.
Other ways to save water is to program sprinklers for three to four minutes at sunrise and sunset, don't water during the heat of day or in windy conditions, and soak the ground no more than four inches deep.
WHAT IS DROUGHT? Drought is a common feature of climate, occurring in areas all over the globe: it is the result of too little rainfall over an extended period of time, often causing water shortages. What exactly constitutes a drought depends in part on what is normal for the region: a drought in the Amazon rainforest may occur after only a week without rain, whereas the Sahara desert can go for weeks with no rainfall and still not be considered to be afflicted with drought.
HOW A DROUGHT COMES ABOUT: Drought doesn't have a single cause; rather, it happens as several contributing factors converge all at once. But the most immediate cause is high atmospheric pressure. When the air sinks, producing high pressure, this keeps clouds from forming, so there is less humidity and therefore less rainfall. This is often seasonal in many regions of the world, but the Sahara and Kalahari deserts in Africa, and Asia's Gobi desert, for example, experience high pressure for most of the year. How long a drought lasts depends on how the air and sea interact to transfer moisture to the air, and how much moisture the soil retains in a given region, among other factors.
PREDICTING A DRY SPELL: Because there are so many factors that come into play, scientists can't really predict a drought in a particular region more than a month or so in advance. To make a prediction, they need to be able to forecast both rainfall (precipitation) and temperature, yet climate patterns change all the time as the result of the slightest shifts in conditions.
TIPS FOR SAVING WATER:
- Turn off the faucet while shaving or brushing your teeth
- Wash only full loads of dishes and laundry
- Fix dripping and leaking faucets and toilets
- Take shorter showers
- Wash cars less frequently
- Keep fire hydrants closed
- Water lawns and gardens on alternate evenings, not every day
- Raise your lawn mower blade height; longer grass needs less water
The American Geophysical Union contributed to the information contained in the TV portion of this report.