Georgia farmers will need 20 percent more water than they're currently using to produce their crops during the next four decades, according to a University of Georgia report released this past summer.

The report, which forecasts water needs from 2011 through 2050, was commissioned by the Georgia Environmental Protection Division and produced by a team of university crop and weather specialists. The purpose of the report is to provide information to the state's water council, which will consider the report as they develop water plans for their regions. These plans will then be added to the overall state plan, in addition to forecasts for population and economy, energy use, land use and water and wastewater demands.

The projection covers pecans and major row crops like cotton, peanuts, corn and soybeans, which account for 85 percent of the state's current irrigation water needs. Also included are vegetables, orchards, blueberries, sod farms and nurseries.

According to the report, the kind of long-term data needed to make econometric projections using national, regional or Georgia models has never been collected for these crops. Projections of irrigated area for these crops simply assumed they would continue to be produced in the areas where they are now grown and future growth rates would equal the aggregate growth rate of the major crops. In this way, water demand for vegetable and specialty crops could be included with major crops for total water withdrawal computations.

Each year's projection includes a wet year, a normal year and a dry year because water planners must prepare for the range of weather conditions that might reasonably be encountered in future years. For example, if 2011 is a dry year from spring through fall, farmers will need 800 million gallons of water per day from underground sources and 300 million gallons per day from surface sources, according to the forecast. If 2050 is a dry year, they will need 1 billion gallons per day from underground sources and 400 million gallons per day from surface water.

Additionally, reports with individual county data provide the monthly withdrawals, detailed crop projections, current irrigated field area, and seasonal irrigation application depths for major crops.

Current irrigated areas were measured on 2007-2008 aerial imagery using fields that had been identified as irrigated by farmers, the Georgia Environmental Protection Division's Agriculture Water Permitting Unit, the Georgia Soil and Water Conservation Commission's Agriculture Meter Program and University of Georgia Ag Water Demand GIS efforts. These visible, irrigated field areas were easily labeled by location within sub-watersheds and counties with standard GIS tools. Those labels enabled summaries to be made for regions with hydrologic and with political boundaries.

Proportion of existing irrigated area of each crop was taken from the 2008 UGA Cooperative Extension Irrigation Survey. This assured that the initial (or baseline) irrigated crop types were consistent with those observed in each county in 2008.

It's expected that future irrigation will occur in areas where the practice is already established, especially in southwest Georgia, where the majority of the state's row crops and vegetable are produced. The area's water needs are supplied by the Floridan aquifer, one of the largest water supplies in the United States, starting near Georgia's fall line and running east into extreme South Carolina and south through Florida.

The projected growth rate for each year for each crop was based on the arithmetic average of projections from three economics-based computer models. The models predicted total Georgia production area for each crop based on United States, Southeast Regional and Georgia data. The national predictions, from USDA, reflect market conditions and worldwide demand for major commodities. The Regional and Georgia models better reflect choices among crops as made by Southeast and Georgia farmers.

For each major crop type, irrigation schedules and monthly totals were computed for weather conditions during each of the years from 1950 through 2007. These represent some extreme droughts as well as some years where little or no irrigation would have been used.

In examining values presented for wet, average and dry years, the report states, it is important to recognize that these represent means of irrigation that could be expected by farmers in that county. Individual fields may receive more or less irrigation depending upon timing of rain received at the field, farmer's yield goals, costs for setting up and applying irrigation, availability of water from source supplies like ponds and streams, and other factors.

In the report, irrigation demand was reduced for farmers using only surface water for their irrigation. These farmers are limited by water available in streams or rainfall that refills their ponds. In dry periods when irrigation is needed, these supplies are often inadequate. Typically, and in forecast computations, surface irrigators use 70 percent as much as those using wells.

Looking at historical trends, irrigation use increased dramatically in Georgia in the 1970s and 1980s, when irrigated acres jumped from 200,000 to 1 million. In the time since then, there has been a steady increase in irrigation use, to the current 1.5 million acres.

The UGA team who prepared this forecast include: James E. Hook, crop and soil sciences and NESPAL; Gerrit Hoogenboom and Joel Paz, department of biological and agricultural engineering; Jeffrey Mullen and John Bergstrom, agricultural and applied economics; and Mark Risse, biological and agricultural engineering-Extension. They were assisted by Melba Salazar and Axel Garcia y Garcia, BAE; Ruohong Cai, AAE; and Shane Conger and Annie Horak, NESPAL; and Adam Speir, CES.