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.