Figure 8: Corn and soybean areas experiencing 2012’s drought in the US.
The U.S. National Drought Mitigation Center’s study in July 2012 (Figure 8) revealed that about 87% of soybeans cultivated in the U.S. were produced in regions affected by drought, as indicated by historical NASS crop production statistics (USDA, 2012). In addition, on July 31, 2012, Iowa’s drought coverage nearly reached 100% throughout the reproductive stage of soybeans, from flowering to setting pods.

Spatial Distribution Analysis

A detailed understanding of the spatial and temporal distribution of drought indices is essential for evaluating localized drought impacts on agricultural productivity. This subsection focuses on the spatio-temporal variability of key drought indices, including the Standardized Precipitation Index (SPI-3) and the Standardized Precipitation-Evapotranspiration Index (SPEI-3), across Iowa from 2000 to 2022. These indices provide critical insights into short-term precipitation anomalies and moisture demand, offering a comprehensive framework to assess trends, regional variability, and anomalies influencing crop yields over the study period.

Spatio-Temporal Patterns of Drought Indices

Figure 9 illustrates the spatial and temporal variability of the Standardized Precipitation Index (SPI-3) across Iowa from 2000 to 2022, providing insights into short-term precipitation anomalies. The maps reveal significant fluctuations in drought intensity, with severe and moderate droughts dominating 2003, 2012, and 2020, particularly in the southern and western regions. These patterns align with periods of persistent dryness, coinciding with notable yield reductions in these areas. Conversely, wet years like 2008, 2010, and 2014 show widespread excessive rainfall, which supported higher yields but also risked flooding, emphasizing the dual challenges of extreme moisture variability.
Figure 10 complements this analysis with the Standardized Precipitation-Evapotranspiration Index (SPEI-3), incorporating the effects of temperature and atmospheric moisture demand. While trends generally align with SPI-3, SPEI-3 highlights the amplified severity of droughts, particularly in 2012, due to elevated evapotranspiration. The index reveals critical differences during wet years like 2010 and 2014, underscoring the role of temperature in either mitigating or exacerbating drought impacts. Localized dry spells in 2007 and 2017 suggest regional climate variability influenced by changing atmospheric conditions.