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.