Refining effective precipitation estimates for a model simulating conservation of groundwater in the Mississippi Delta Shallow Alluvial Aquifer

Author(s): Wax, C.; Pote, J.; Thornton, R.

The shallow alluvial aquifer in the Mississippi Delta region is heavily used for irrigation of corn, soybeans, and cotton, as well as for rice flooding and filling aquaculture ponds in the prominent catfish industry. Water volume in the aquifer is subject to seasonal declines and annual fluctuations caused by both climatological and crop water use variations from year-to-year.

Available climate, crop acreage, irrigation water use, and groundwater decline data from the 19 counties in the Delta were used to construct a model that simulates the effects of climatic variability, crop acreage changes, and specific irrigation methods on consequent variations in the water volume in the aquifer. Climatic variability was accounted for by predictive equations that related annual measured plant water use (irrigation) to total growing season precipitation amounts. This derived relationship allowed the application of a long-term climatological record (50 years) to simulate the cumulative impact of climate on groundwater use for irrigation.

The relationship between rainfall and anticipated crop water use was initially estimated by a simple regression between total growing season rainfall and measured irrigation water use for the period 2002-2007, with a resulting R2 value of 0.93. Adding data from 2008 caused R2 to drop to 0.63. It was recognized that total growing season rainfall was not representative of the timing, or episodic nature, of rainfall compared to plant water demand day-by-day through the growing season. To account for this timing issue, weekly rainfall amounts were compared to weekly expected crop water demand to produce an effective rainfall estimate. The resulting improvements are shown. This effective rainfall compared to irrigation use is expected to provide a much-improved rainfall-irrigation coefficient for use in the model.

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Technical Sessions

Session I Sedimentation
Session II Weather/Climate
Session III Coastal Resources
Session IV Surface Water Management
Session V Wetlands
Session VI Education
Session VII Management/Planning
Session VIII Wetlands
Session IX Delta Groundwater
Session X Nutrients
Session XI Delta Water Resources
Session XII Ports

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