Sensing Droughts

E-mail Melanie Martella

You know, one of the things I love most about the Web is how easy it is to find information that you never knew existed. Case in point: a link to an excellent article from the USDA Agricultural Research Service (ARS) on evapotranspiration maps (maps of the moisture released from the plants and ground) that I found in a U.K. poultry farming magazine.

I have to admit, I'm not a huge fan of poultry except as a foodstuff. When I was a kid, the chickens on the farm next door to our house were dim and mean; the geese were terrifying; and the guinea fowl were decorative and so confused that they adopted a male pheasant as the leader of their flock. (The pheasant was no better; as far as we could tell he thought that the guinea fowl were female pheasants.) Just like farmers, however, I am a big fan of water and having enough of it. Last year, for example, was a bad, bad year for drought in several places in the U.S. and if you look at the Drought Monitor Map you'll see that parts of the west, midwest, and especially the southern U.S. are still wrestling with drought conditions and will continue to do so.

Drought conditions don't just spell trouble for farmers and residents, they also make wildfires more likely. In 2006, the National Integrated Drought Information System (NIDIS) Act was signed into law. As part of the effort to create the drought information system, the U.S. Drought Portal has been created, acting as a central information clearing house for drought conditions, forecasting, education, and support. So where does evapotranspiration and the mapping of same come in? It turns out that if you measure the land-surface temperature from space, and couple it with remote-sensing data on vegetation cover, you can get a good idea of how much evapotranspiration is occurring; wet soil is cooler than dry soil, stressed plants are warmer than healthy ones. The maps, generated from the Atmosphere-Land Exchange Inverse (ALEXI) computer model developed by Martha Anderson and Bill Kustas of the USDA ARS, are similar to traditional hydrologic maps but require less data and less complex mathematical models to produce. (I'd suggest reading the article "A New Way to Map Drought and Water Use Worldwide" in the February 2012 issue of the Agricultural Research Magaizine to get a better idea of why this model is so cool.)

With so many weather patterns changing, the ability to assess what's happening with your water supply helps with food production, water management, risk mitigation, and (eventually) with weather forecasting. ALEXI and the satellite data it uses could be a valuable tool in making these assessments but only if we maintain the satellites and their remote-sensing instruments.