Lag-aware integrated agricultural drought index using satellite precipitation products

Agricultural drought poses a growing threat to food security and water resource management; however, conventional drought indices often fail to capture the temporal dynamics of drought propagation and lag between index signals and agricultural impact. This study proposes the integrated agricultural drought index (IADI), a lag-aware framework for spatially continuous agricultural drought assessment using satellite-based precipitation data over South Korea. Five satellite precipitation products were first evaluated against observations from 56 ground stations for 2010–2023. Drought frequency, duration, and severity were then derived from SPEI-3, SPEI-6, SPEI-12, and SMI using run theory across 4012 grid cells for 1996–2024 and combined into index-specific drought severity indices. Temporal alignment between each index and observed agricultural droughts was quantified using receiver operating characteristic–area under the curve (ROC–AUC) analysis across 60 administrative districts. The resulting lag information was subsequently incorporated into three objective weighting schemes through a response adjustment coefficient that penalized larger temporal offsets. The results showed that CHIRPS v3.0 achieved the best overall performance and was selected as the precipitation input. All indices achieved AUC values above 0.7. SMI and SPEI-12 showed mean leading lags of −1.00 and −2.97 months, respectively, whereas SPEI-3 and SPEI-6 showed concurrent to slightly lagging responses. The resulting IADI classifications were highly consistent across the three weighting schemes, with 90.65% of grid cells assigned to the same drought class. The spatial distribution of IADI values also broadly corresponded with historical agricultural drought records. The proposed framework may provide a lag-informed approach for agricultural drought monitoring, with potential applicability to other regions where satellite-based precipitation data and agricultural drought reference records are available.