Figure 5: Mean correlation coefficients for corn and soybean
yields.
The results also show that SPI-1 and SPEI-1 have limited predictive
value for soybeans but significantly influence corn yields. These
findings underscore the importance of selecting appropriate drought
indices tailored to specific crops and growth stages to enhance drought
forecasting and risk management strategies.
Spatio-Temporal Patterns of Drought
Indices
Figures 6–11 illustrate the spatiotemporal distribution of SPI-3,
SPEI-3, and PDSI values, providing insights into the geographical and
temporal variability of drought impacts on crop yields in Iowa.
SPI-3 and SPEI-3 Trends
Figure 6 shows the temporal trends of SPI-3 and SPEI-3, capturing
short-term precipitation anomalies and their combined temperature
effects. Positive values indicate wet conditions, while negative values
denote drought conditions. The 2012 drought is particularly notable,
with severe negative values reflecting extreme dryness. Wet years, such
as 2010 and 2014, correlate with increased crop yields, highlighting the
critical role of moisture availability.