Effects of irrigation and drought on Illinois ground-water resources are examined. Irrigation water use for five soil types is estimated from a monthly water budget model on the basis of precipitation and temperature data. Irrigation water use from each township with irrigated acreage is added to municipal and industrial ground-water use data and then compared to aquifer potential yields. A statewide geographic information system is used for the spatial analysis. The model is tested for sensitivity to climate variation; seasonal water deficits are calculated by using data from extreme growing seasons and extended droughts. The effect of increasing the amount of irrigated land is also considered. The effects of variable irrigation demand on ground-water resources are expressed as use/yield ratios, to highlight regions most susceptible to ground-water stress because of drought or increased irrigation. Results show that irrigation is a substantial seasonal consumptive ground-water use in Illinois. but effects are localized and highly dependent on climate variability. Some potential for seasonal or temporary overpumpage may exist in the most heavily irrigated areas during years with below-normal precipitation or during extended droughts. However, theaquifers being used for irrigation appear to be able to recover from high seasonal demands for irrigation water without suffering significant depletion. Exceptions to this may occur during extended drought periods, especially if widespread expansion of irrigation practices occurs. Reference: Bowman, Jean A., and Mark A. Collins. Impacts of Irrigation and Drought on Illinois Ground-Water Resources. Illinois State Water Survey, Champaign, Report of Investigation 109,

Abstract: Effects of irrigation ,and ,drought ,on Illinois ,ground-water ,resources ,are examined. ,Irri- gation,water ,use for five soil types ,is estimated ,from ,a monthly ,water ,budget ,model ,on the ,basis ofprecipitation, and ,temperature ,data. Irrigation ,water ,use ,from ,each ,township ,with ,irrigated acreage,is added ,to municipal ,and ,industrial ,ground-water ,use ,data and ,then ,compared ,to aquifer potential,yields. A statewide ,geographic ,information ,system ,is used ,for the spatial ,analysis. The model,is tested ,for sensitivity ,to climate ,variation; seasonal ,water ,deficits are calculated ,by using data,from ,extreme ,growing ,seasons ,and ,extended ,droughts. ,The effect ,of increasing ,the amount ofirrigated,land ,is also ,considered. ,The effects of variable ,irrigation demand ,on ground-water ,re- sources are expressed as use/yield ratios, to highlight regions most susceptible to ground-water stress because ,of drought ,or increased ,irrigation. Results show ,that irrigation ,is a ,substantial ,sea- sonal,consumptive ,ground-water ,use ,in Illinois. but ,effects are localized ,and ,highly ,dependent ,on climate,variability. Some ,potential ,for seasonal ,or temporary ,overpumpage ,may ,exist in the ,most heavily,irrigated ,areas during ,years ,with ,below-normal ,precipitation ,or during ,extended ,droughts. However, theaquifers being used for irrigation appear to be able to recover from high seasonal de- mands,for irrigation ,water ,without ,suffering ,significant ,depletion. ,Exceptions ,to this ,may ,occur during extended drought periods, especially if widespread expansion of irrigation practices occurs. Reference: Bowman, Jean A., and Mark A. Collins. Impacts of Irrigation and Drought on Illinois