Optimal water allocation for joint sustainability of irrigated agriculture and urban growth
Date
2017
Authors
Mahmoudzadeh Varzi, Manijeh, author
Oad, Ramchand, advisor
DeJonge, Kendall, committee member
Grigg, Neil, committee member
Laituri, Melinda, committee member
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Abstract
Historically, agriculture was the main water consumer in Colorado. But the state's demand for water has increased because of rapid urban growth and development of oil and gas industry. Urban communities started buying agricultural water rights to satisfy their growing demands. However, alternative land uses for farms without water right are limited and often they are left fallow. Colorado's newly finalized water plan recognizes agriculture dry-up as one of the primary water challenges of the state and supports projects that explore alternatives to the permanent transfer of agricultural water rights to municipal and industrial users. This research has investigated deficit irrigation and limited irrigation strategies as methods of reducing farm water consumption as well as methods of temporary transfer of water, viable under Colorado's Water Law. These two sets of information formed a conceptual framework for defining an effective transfer method. An economic model was developed to determine optimal water partitioning between on-farm water uses and off-farm water renting. The model proves partitioning water is only optimal when crop water production function is concave; for linear functions the optimal option is to allocate all farm water to the most profitable. Field experimentation has determined the effect of water scarcity on agricultural production and revenue. In particular, crop yield response to water stress was quantified in experimental farms for three common crops in Colorado: corn, sunflower, and sorghum-sudangrass. The filed observations support a linear crop water production function for sorghum-sudangrass and a concave function for corn and sunflower with corn function being more concave than sunflower function. The economic model was used for South Platte River Basin to determine the minimum renting price of water for water partitioning to be optimal. The results show current renting prices of water in South Platte River Basin are too low and need to increase to more than six times before partitioning of water becomes a worthwhile practice. It was also concluded that two set of engineering tools are required for implementation of deficit irrigation; 1) tools to accurately apply desired amount of water, and 2) tools to measure farm consumptive use on a daily basis. At institutional level, Colorado Water Law's no-injury and anti-speculation rules need to be simplified for deficit irrigation to be a worthwhile alternative method to buy-and-dry.
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Subject
deficit irrigation
crop water production function