Climate-driven redistribution of foxtail millet (Setaria italica) suitability in China revealed by biomod2 ensemble models: implications for dryland crop adaptation.

Foxtail Millet (Setaria italica) is one of China's earliest domesticated cereal crops and remains important for dryland farming, germplasm conservation, and climate-resilient agriculture. However, climate warming and altered precipitation regimes may reshape its agroclimatic suitability and challenge traditional production regions. Here, we integrated 1, 948 cleaned occurrence records with climatic, topographic, soil, and UV-B radiation variables, and used the biomod2 ensemble species distribution modelling framework to predict the potential suitable distribution of S. italica across China. Projections were conducted under the historical baseline and CMIP6 BCC-CSM2-MR future climate scenarios for SSP1-2.6, SSP2-4.5, SSP3-7.0, and SSP5-8.5 across the 2030s, 2050s, 2070s, and 2090s. The selected EMwmeanByTSS ensemble showed good discrimination ability and acceptable predictive performance, with validation ROC and TSS values of 0.863 ± 0.011 and 0.581 ± 0.022, respectively. Annual precipitation (bio12, 29.61%), elevation (elev, 28.07%), minimum temperature of the coldest month (bio06, 14.23%), and UV-B seasonality (uvb2, 10.93%) were the dominant predictors, jointly contributing 82.82%. Under the historical baseline, the total potential suitable area was 4.09 × 106 km² (44.22% of China's land area), with highly suitable areas concentrated in the North China Plain, eastern Loess Plateau, and southern margin of Northeast China. Under future SSP scenarios, the total suitable area increased to 4.29 × 106 - 4.87 × 106 km², representing a 4.77%-18.87% increase. Expansion was mainly projected along the northern and peripheral margins of the current suitable region, while contraction occurred along southern, southwestern, and transitional margins. The suitability centroid shifted slightly northward to northwestward from northern Henan toward southern-central Shanxi, with net displacement of 113.33-232.79 km by the 2090s. Overall, future suitability is projected to show a pattern of stable core areas, marginal expansion, localized contraction, and limited centroid migration. These findings provide a spatial basis for stable production-region protection, regional variety trials, germplasm conservation, and climate-adaptive dryland agricultural planning.