**1. Introduction**

Nutrients, such as nitrogen (N), are necessary in farming for raising crop and forage productivity, but they can also bring potential harm to the socioeconomic system. A hypoxic zone is a phenomenon where low dissolved oxygen (hypoxia) occurs in aquatic environments, which is primarily caused by excess nutrients running off or leaching from the contributing watershed. Over 400 hypoxic zones have been found in the world and the problem of hypoxia is worsening [1]. In the US, the environment and socioeconomic system of the Gulf of Mexico are impacted by hypoxia which has one of the largest hypoxic zones in the world [2]. Nitrogen (N) is one of the major contributors to the creation of the hypoxic zone of the Gulf of Mexico through the nitrates (NO3) lost from watersheds within the Mississippi River Basin, which moves downstream to the Gulf of Mexico [3]. Studies show that the state of Iowa, one of the major producers of corn, soybean, ethanol, and animal products, contributes a considerable amount of nitrogen loads to the Mississippi River basin [4,5]. As the largest producer of corn in the US, nearly 57% of Iowa's corn is used for ethanol production [6]. The manure produced by animal agriculture is also rich in nitrogen [7]. The current research aims at creating strategies and policies to mitigate the excess nitrogen originating from the Iowa food-energy-water (IFEW) system.

Climate variability has major effects on FEW systems. For example, extreme events, such as floods or droughts, can reduce water availability and quality. In southern East

**Citation:** Raul, V.; Liu, Y.-C.; Leifsson, L.; Kaleita, A. Effects of Weather on Iowa Nitrogen Export Estimated by Simulation-Based Decomposition. *Sustainability* **2022**, *14*, 1060. https:// doi.org/10.3390/su14031060

Academic Editor: Julian Scott Yeomans

Received: 11 December 2021 Accepted: 8 January 2022 Published: 18 January 2022

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Africa, infrastructure design is challenging due to multi-year drought [8]. Furthermore, changes in the weather impact energy usage and demands of human activities. Moreover, in the food system, the needs for livestock watering and crop fertilizer can be severely impacted due to climates changes. Though Iowa uses primarily rain-fed agricultural production, in other areas irrigation water for crops is also significantly impacted (both in supply and in requirements) by weather and climate. Arizona is a predominantly irrigated agriculture state and supplies food to at least six major cities. It is especially vulnerable to climate changes [9]. Therefore, it is important to investigate the effects of weather variability on the sustainable management of FEW systems.

It is important to capture the complex interactions of the different domains to determine the exported nitrogen of the system. In this work, weather, water, agriculture, animal agriculture, and energy are considered in modeling the IFEW system. The macro-level simulation-based IFEW model introduced in [10] to determine the surplus nitrogen in the state of Iowa is extended to include a crop-weather model using linear regression of historical weather parameters, which is based on a prior study [11]. Simulation decomposition (SD) [12,13] is used to visualize the effects of weather variability on the IFEW nitrogen export. Furthermore, SD analysis is used to distinguish the influences of different weather scenarios affecting the surplus nitrogen.

The next section gives the details of the IFEW system model and the SD analysis technique. The following section presents the numerical results of SD applied to the proposed IFEW simulation model for several weather scenarios. The last section summarizes the work and discusses potential future work.
