AGRICULTURAL IRRIGATION WATER DEMAND
Georgia's Major and Minor Crops
2011 through 2050
The data and reports below were prepared under University of Georgia contracts with the Georgia Environmental Protection Division and the Georgia Environmental Facilities Authorities (038952-01 and 038950-01). The purpose of the contracts was to prepare forecasts of irrigation water demand that will meet the needs of the agricultural sector for the Georgia economy during the first half of this century. The projections cover the row and orchard crops as well as most vegetable and specialty crops that cover more than 95% of Georgia's irrigated land.
The UGA team who prepared this forecast include: Dr. James E. Hook, Crop and Soil Sciences and NESPAL; Dr. Gerrit Hoogenboom and Dr. Joel Paz, Department of Biological and Agricultural Engineering; Dr. Jeffrey Mullen and Dr. John Bergstrom, Agricultural and Applied Economics; and Dr. Mark Risse, Biological and Agricultural Engineering-Extension.
They were assisted by Dr. Melba Salazar and Dr. Axel Garcia y Garcia, BAE; Ruohong Cai, AAE; and Shane Conger and Annie Horak, NESPAL; and Adam Speir, CES.
Projected Agricultural Water Withdrawals
|Agricultural irrigation water demand was projected for groundwater and for surface water sources for the years 2011, 2020, 2030, 2040, and 2050. 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. Summaries are provided by Water Planning Regions and Counties, as well as DNR's designated Local Drainage Areas. Additionally, reports with individual county data provides the monthly withdrawals, number of systems and area irrigated by selected equipment, major sources, projected irrigated field area, and seasonal irrigation application depths for major crops.|
Summary of AWD contract development, approach, and public involvement, May, 2010.
Irrigation Withdrawals by WPR
Summary of annualized irrigation withdrawals by source
as expected for wet, normal, and dry years.
Summarized from detailed county reports (next).
Irrigation withdrawals and details by counties
Details of crops, irrigated acres, water sources,
and irrigation depths, county-by-county.
Irrigation Withdrawals by Local Drainage Areas
Summary of annualized irrigated withdrawals by source
expected for wet, normal, and dry years
as partitioned by defined LDA boundaries.
Presentation on Ag Water Demand
Summary of approach and data as presented at the 3rd meeting of the Regional Water Councils, September, 2009.
How were these projections made?
Withdrawal quantities were computed for each county or drainage area as the product of three values:
The product, monthly withdrawals (acre-inches) by crop, was summed for the county or drainage area. To be consistent with other water planning efforts, acre-inches per month was converted to million gallons per day (MGD) by converting to gallons/month and dividing by the days in the month. For annualized summaries, withdrawals in million gallons were summed for the year and divided by 365 days.
- Projected irrigated area for a crop (acres),
- Predicted monthly irrigation application depth (inches),
- Proportion of irrigation water derived from a source (fraction).
|Overview of Agricultural Water Use and Demand Forecast|
A "50,000 ft" view of irrigation in Georgia and the forecasting methods used for the future water needs projection
(as presented during 2nd Water Council Meetings in June, 2009.) (A PowerPoint Presentation - 2003 ppt version)
Irrigation Development in Georgia
A timeline of irrigation development and growth in Georgia
and information about irrigation system types used here.
Projected irrigated area for a crop:Projected irrigated area is the product of current irrigated field area in a county or drainage area (acres) X proportion of existing irrigated area of each crop (fraction) X projected growth rate for each year for that crop (fraction).
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 major rotation 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.|
Projected growth rate for each year for each crop was based on the arithmetic average of projections from three economics based 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. Five major crops - corn, cotton, peanut, soybean, and pecan - were included in these three models. These crops make up 85% of Georgia's irrigated crop area.
Vegetable and specialty crops like sod, ornamental nurseries, and berries make up much less of Georgia's water demand than the major crops. Nonetheless, the water demand created by these valuable crops is significant in many areas of Georgia. 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 that they would continue to be produced in the areas where there are now grown and future growth rates would equal the aggregate growth rate of the five major crops. In this way, water demand for vegetable and specialty crops could be included with major crops for total water withdrawal computations.|
|Further Explanations and Data Sets.|
For more complete explanations, data sets used in making these acreage projections,
and data sets produced as intermediary information.These include detailed
irrigated area information in GIS and tabular formats
Predicted monthly irrigation application depth :
||Irrigation amounts were computed and summarized statistically to represent monthly applications that would be needed to meet normal crop water needs in wet, average, and dry years. For each major crop type, irrigation schedules and monthly totals were computed for the weather conditions that existed 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. We prepared summaries for wet, normal and dry years and kept them separated in our demand forecasts. Planners need to be aware of the full range of normal irrigation water demand, since accomodations are needed for all conditions. |
In examining values presented for wet, average, and dry years 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 an irrigation, availability of water from source supplies like ponds and streams, and other factors. In recognition of observated irrigation patterns, we reduced irrigation demand 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 our computations, surface irrigators use 70% as much as those using wells.|
|Further Explanations and Data Sets.|
For more complete explanations, data sets used in making these irrigation depth predictions.
Proportion of irrigation water derived from a source:
||EPD permits wells, stream-side pumps, and pond pumps in their Agricultural Water Withdrawal Permitting program. Each source is identified by its geographic location. The fields receiving irrigation are not permitted. However, EPD and, in conjunction with the state-mandated agriculture meter program, GSWCC have been mapping irrigated fields and associating them with the permitted wells and pumps that supply them. Since the irrigated fields are visible on high resolution aerial images and thus are readily located within counties and drainage areas, the water source distributions can be computed for those counties and drainage areas. Newer, unmapped, irrigated fields are also visible. Many are located adjacent to or contain permitted water sources. When clearly linked, these fields were likewise identified by source.|
|To compute the fraction of a drainage area's or county's irrigation water supply, each field with known source was assigned a fractional water supply. Fields irrigated by wells only were assigned as 100% groundwater, those from surface, 100% surface, and those labeled as ponds refilled by wells were assigned 70% from groundwater and 30% from surface water. These later figures were obtained from Ag Water Pumping monitoring of 45 well-to-pond systems. From 1999 through 2004, these monitored systems pumped the equivalent of 70% of irrigation-applied water from their wells. |
Using the field area-weighted withdrawals from fields with identified sources, a water source fraction - percent from wells, percent from surface sources - was computed for each drainage area or county. These varied from those that obtained 100% of irrigation water from streams and ponds to those that relied almost entirely on groundwater sources. Within each drainage area or county, fields with unknown sources were assigned source ratios that equaled those for known fields in the drainage area or county.
Groundwater sources were further broken down by aquifer (or aquifers) tapped by the well. For most permitted wells, drilling logs, borehole and casing depths, and geologic charts were used by EPD to identify the aquifer uused wiuth each irrigated field. In the same way that water supplies were apportioned between surface and groundwater by permits associated with irrigated fields, groundwater was apportioned between aquifers by permits associated with irrigated fields. The fraction of withdrawal by aquifer was computed for drainage areas and counties.
|Further Explanations and Data Sets.|
For more complete explanations, data sets used in making these water source assignments.
|Ad hoc Water Use Reports for special sectors of the agriculture industry.|
Farm Animal Water Use in Georgia
Ad hoc report on water needs in the
animal production agriculture sector in Georgia.
Golf Course Water Use in Georgia
Ad hoc report on water needs for the
golf courses that hold agriculture permits.
Nursery & Greenhouse Water Use in Georgia
Ad hoc report on water needs in field and container
plant nurseries and greenhouses in Georgia.
How these Ag Water Demand Forecasts Compare with other Surveys and Forecasts?Few forecasts have been made for Georgia's agricultural water use sector in the past. However, for several areas of the state, water demand forecasts were made as part of the court ordered Comprehensive Study for the interstate Alabama-Coosa-Tallapoosa and Appalachicola-Chattahoochee-Flint River Basins water lawsuits.
Three surveys of agriculture water use have been regularly computed in past years. These are the US Geologic Survey's "Water Use in Georgia by County" prepared every five years, UGA's Cooperative Extension Service "Irrigation Survey" prepared every 3 to 4 years, and US Department of Agricultural "Farm and Ranch Irrigation Survey" prepared every five years as a followup to their Agricultural Census.
Previous Ag Water Forecast for Georgia
Ag Water Demand forecasts of planted acres compared with those
made by NRCS in 1996 for the ACT/ACT Comprehensive Study?
(Natural Resources Conservation Service (NRCS). March 1996. ACT/ACF River Basins
Comprehensive Study: Agricultural Water Demand. U.S. Dept. of Agriculture, Athens, GA.)
ACT/ACT versus AWD crop area forecasts for 2010, 2020, and 2050(Excel file)
|Previous Ag Water Use Surveys in Georgia|
USGS Water Use in Georgia for 2005
UGA CES Irrigation Survey for 2008
USDA Farm and Ranch Irrigation Survey for 2003
Last updated 6/29/2010 James E. Hook
Links reconfirmed 11/7/2012 JEH