Figure 4: Annual correlation of soybean yield with different
drought indices.
From 2010 to 2015, notable shifts in climatic trends influenced yield
responses, as evidenced by increasing positive correlations with
shorter-term indices. After 2015, the influence of rapid precipitation
changes (as captured by SPI-1 and SPEI-1) became more apparent,
emphasizing the need for adaptive management strategies that consider
these dynamics.
Mean Correlation Analysis
Figure 5 presents the mean correlation coefficients for corn and soybean
yields with all drought indices over the study period. Soybeans
demonstrate stronger correlations with SPI-6, SPI-12, SPEI-6, and
SPEI-12, highlighting their dependence on long-term moisture
availability. These indices may serve as reliable predictors of soybean
productivity in Iowa under similar climatic conditions.
In contrast, corn yields exhibit less consistent correlations with these
indices, likely due to the crop’s greater sensitivity to short-term
drought conditions. Notably, EDDI shows a strong negative correlation
with corn yields, reflecting the crop’s susceptibility to high
evaporative demand during critical growth phases. This aligns with
corn’s higher water requirements and sensitivity to drought-induced
stress.