Results and Discussion
This chapter presents the correlations between drought indices and crop
yields, their spatio-temporal variability, and the implication for
understanding drought impacts on agricultural productivity. The findings
are discussed in detail to highlight the significance of both short- and
long-term drought indices for corn and soybean yields. Insights into
climatic conditions, spatial patterns, and implications for drought risk
management are also explored.
Yearly Correlation of Corn Yields with Drought
Indices
Figure 3 illustrates the yearly correlation coefficients between corn
yields and various drought indices from 2000–2022. Shorter-term
indices, such as SPI-1 and SPEI-1, exhibit greater variability in
correlations, with significant swings in positive and negative values.
These trends indicate that corn production is susceptible to short-term
precipitation variability, particularly during critical growth stages
such as silking and grain filling. For instance, corn is highly reliant
on moisture availability during its reproductive phase, and a lack of
rainfall during these periods can result in substantial yield
reductions.
In contrast, longer-term indices like SPI-12 and SPEI-12 reflect the
cumulative impact of extended moisture conditions. These indices capture
broader seasonal or yearly precipitation trends, which align with the
water requirements of corn during the entire growing season. Notably,
sharp peaks and troughs in 2005, 2012, and 2018 correspond to years of
significant climatic anomalies. For example, the severe drought of 2012,
widely regarded as one of the most impactful droughts in U.S. history,
resulted in significant negative correlations across most indices,
underscoring the vulnerability of corn to prolonged droughts.