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1. Center Pivot Irrigation Systems as a Form of Drought Risk Mitigation in Humid Regions

   Cooley, Daniel; Smith, Steven M. (January 2022, AMERICAN AGRICULTURE, WATER RESOURCES, AND CLIMATE CHANGE)

   Libecap, Gary D.; Dinar, Ariel (Ed.)

   Farmers in humid states of US, traditionally reliant on rainfall, have more than tripled irrigation since 1978. We examine this trend in Illinois where there has been a nearly threefold increase in center pivot irrigation system (CPIS) installations since 1988. Specifically, we analyze where and when CPIS installations occur and their benefits in terms of crop yield, irrigated acreage, crop selection, and changes to drought-related insurance payouts. To do so, we create a novel data set derived from a deep learning model capable of automatically identifying the location of CPIS during drought years. The results indicate CPIS installations are significantly more common over alluvial aquifers after droughts. Some evidence supports CPIS leads to corn appearing more often in the corn-soy crop rotation. Counties with a higher presence of CPIS do not have higher average crop yields. However, in drought years CPIS presence does have a significant positive effect on corn yield and a significant negative effect on indemnity payments for both soybeans and corn. The results provide insights into an emerging trend of irrigation in humid regions, raising potential policy considerations for crop insurance and signaling a potential need to address water rights as demand increases. 

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2. Increased Dependence on Irrigated Crop Production Across the CONUS (1945–2015)

   https://doi.org/10.3390/w11071458  

   Smidt, Samuel J.; Kendall, Anthony D.; Hyndman, David W. (July 2019, Water)

   Efficient irrigation technologies, which seem to promise reduced production costs and water consumption in heavily irrigated areas, may instead be driving increased irrigation use in areas that were not traditionally irrigated. As a result, the total dependence on supplemental irrigation for crop production and revenue is steadily increasing across the contiguous United States. Quantifying this dependence has been hampered by a lack of comprehensive irrigated and dryland yield and harvested area data outside of major irrigated regions, despite the importance and long history of irrigation applications in agriculture. This study used a linear regression model to disaggregate lumped agricultural statistics and estimate average irrigated and dryland yields at the state level for five major row crops: corn, cotton, hay, soybeans, and wheat. For 1945–2015, we quantified crop production, irrigation enhancement revenue, and irrigated and dryland areas in both intensively irrigated and marginally-dependent states, where both irrigated and dryland farming practices are implemented. In 2015, we found that irrigating just the five commodity crops enhanced revenue by ~$7 billion across all states with irrigation. In states with both irrigated and dryland practices, 23% of total produced area relied on irrigation, resulting in 7% more production than from dryland practices. There was a clear response to increasing biofuel demand, with the addition of more than 3.6 million ha of irrigated corn and soybeans in the last decade in marginally-dependent states. Since 1945, we estimate that yield enhancement due to irrigation has resulted in over $465 billion in increased revenue across the contiguous United States (CONUS). Example applications of this dataset include estimating historical water use, evaluating the effects of environmental policies, developing new resource management strategies, economic risk analyses, and developing tools for farmer decision making. 

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3. Divergent changes in crop yield loss risk due to droughts over time in the US

   https://doi.org/10.1088/1748-9326/ad7618  

   Rathore, Lokendra_S; Kumar, Mukesh; Moftakhari, Hamed; Ganguli, Poulomi (September 2024, Environmental Research Letters)

   Abstract Drought poses a major threat to agricultural production and food security. This study evaluates the changes in drought-induced crop yield loss risk for six crops (alfalfa, barley, corn, soybean, spring wheat, and winter wheat) between 1971–2000 and 1991–2020 across the contiguous US. Using a copula-based probabilistic framework, our results reveal a spatially heterogeneous change in yield risk to meteorological droughts, which varies with crop types. Regional analyses identify the largest temporal decline in yield risk in the Southeast and Upper Midwest, while the Northwest and South show an increase in risk. Among the considered anthropogenic and climatic drivers of crop productivity, changes in climatic variables such as high temperatures (e.g., killing degree days), vapor pressure deficit and precipitation show significantly stronger associations with changes in yield risk than irrigated area and nitrogen fertilizer application. Among the counties that observe drier drought events, only 55% exhibit an increase in crop yield loss risk due to drier droughts. The rest 45% show a decrease in yield loss risk due to mediation of favorable climatic and anthropogenic factors. Alarmingly, more than half (for barley and spring wheat), and one-third (for alfalfa, corn, soybean and winter wheat) of that the risk increasing regions have outsized influence on destabilizing national crop production. The findings provide valuable insights for policymakers, agricultural stakeholders, and decision-makers in terms of the potential ways and locations to be prioritized for enhancing local and national agricultural resilience and ensuring food security. 

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4. The Impact of Irrigation on Surface Nitrate Export from Agricultural Fields in the Southeastern United States

   https://doi.org/10.3390/land14020392  

   Ellenburg, W Lee; Cruise, James F; Ortiz, Brenda V; Suhs, Rachel (February 2025, Land)

   Agricultural runoff ranks second only to atmospheric deposition as a source of nitrogen pollution to streams in the southeastern United States. Climate-smart practices such as irrigation have the potential to reduce these impacts and provide resilience in the face of climate change. The purpose of this study is to evaluate the impact of irrigation amounts and fertilizer application strategies on surface nitrate export to surrounding steams. Data from an existing experiment on corn nitrogen fertilization in the Southeastern US was utilized and a crop simulation model was employed to simulate the water and nitrogen dynamics within the soil with particular emphases on nutrient uptake and residual nutrients. left in the soil after harvest under varying fertilization scenarios. A hydrologic and nutrient export model was developed to run in conjunction with the crop model to simulate lateral export from the fields. The results of this study indicate that climate and nutrient management are the dominant factors in determining surface nutrient transport under both rain fed and irrigated conditions, confirming previous studies. The overall results show that irrigation, on average, reduced nutrient export from the surface, especially in dry years. The effect is even greater if the nutrients are applied later in the year while irrigation is on-going. While this present study provides an initial look at the potential impacts of irrigation on nutrient export in humid areas, the available on-farm observational data is limited in its content. However, the results obtained support existing literature and provide further evidence on the impact of irrigation as a climate resilient practice and will help direct future studies in the region. 

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5. Addressing Challenges for Mapping Irrigated Fields in Subhumid Temperate Regions by Integrating Remote Sensing and Hydroclimatic Data

   https://doi.org/10.3390/rs11030370  

   Xu, Tianfang; Deines, Jillian; Kendall, Anthony; Basso, Bruno; Hyndman, David (February 2019, Remote Sensing)

   High-resolution mapping of irrigated fields is needed to better estimate water and nutrient fluxes in the landscape, food production, and local to regional climate. However, this remains a challenge in humid to subhumid regions, where irrigation has been expanding into what was largely rainfed agriculture due to trends in climate, crop prices, technologies and practices. One such region is southwestern Michigan, USA, where groundwater is the main source of irrigation water for row crops (primarily corn and soybeans). Remote sensing of irrigated areas can be difficult in these regions as rainfed areas have similar characteristics. We present methods to address this challenge and enhance the contrast between neighboring rainfed and irrigated areas, including weather-sensitive scene selection, applying recently developed composite indices and calculating spatial anomalies. We create annual, 30m-resolution maps of irrigated corn and soybeans for southwestern Michigan from 2001 to 2016 using a machine learning method (random forest). The irrigation maps reasonably capture the spatial and temporal pattern of irrigation, with accuracies that exceed available products. Analysis of the irrigation maps showed that the irrigated area in southwestern Michigan tripled in the last 16 years. We also discuss the remaining challenges for irrigation mapping in humid to subhumid areas. 

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