| Archives | Main Page | Graphics Intensive Version | Home |
| Roundup |
|
Finally, a better way to estimate crop water use Irrigators who want to transfer their water rights to non-agricultural users can oftentimes sell only as much water as their crops have historically required. These growers need precise figuresÑas do producers planning for the irrigation requirements of new varieties or crops. Yet estimates of water "consumed" by a crop have historically been based simply on air temperature: the hotter the weather, the more water the crop presumably used. But it's not just the heat, as they say. It's also the relative humidity, solar radiation, and wind speed that determine how much water a crop demands. (Photo above) Water pumped from the Snake River irrigates potatoes in a field near Glenns Ferry. David R. Frazier Photography At the University of Idaho's Kimberly Research and Extension Center, water resources engineer Rick Allen is adding that data to existing temperature and precipitation data for each of 110 local weather stations statewide. Using the "Penman equation"Ñoriginally adapted to Idaho conditions by USDA-Agricultural Research Service soil scientist Jim WrightÑAllen extrapolates the local humidity, radiation, and wind speed data from a historical base of these measures collected at about 10 regional weather stations. The result: each of the 110 local weather stations will have complete sets of weather data for the past 30 to 50 years. Producers can check estimated crop water-use figures for their nearest local weather station to learn how much water each of their own crops uses at peak demand and over the entire season. Allen expects to post the data on University of Idaho Web site www.kimberly.uidaho.edu this summer. The enhanced numbers should prove valuable to scientists conducting groundwater modeling studies as well as to growers. "Producers need to know how big to size a canal, a pump, or a pipeÑand how big a center pivot system needs to be," says Allen. And, when the next drought comes, the updated consumptive-use data should help water managers make better decisions. "If they know the amount of water that senior-right users actually consume, they may be able to mediate negotiations between senior- and junior-right holders so they won't have to shut off the junior users quite as soon," Allen says. "EconomicallyÑhopefullyÑit will be a more efficient system to manage." -Marlene Fritz
|