Nonlinear response of human ecology to Holocene climate change in Africa

The African Humid Period (AHP; ∼14.8–5.5 kyr BP) transformed the Sahara from a hyperarid desert into a wooded savanna, enabling widespread human habitation. Yet links between hydroclimatic variability and demographic response remain poorly understood at the continental scale. Here, we integrate multi-proxy paleoclimate records (leaf-wax hydrogen isotopes (δDwax), oxygen isotopes (δ¹⁸O), and diatom assemblages) from 36 sites with 15,007 radiocarbon-dated archaeological assemblages, to reconstruct climate–human dynamics across northern and tropical Africa over the past 16 kyr. Statistical modeling and time-series analyses reveal that major humid maxima (12–10 kyr BP) coincided with continent-wide population expansions (11–5 kyr BP), while mid- to late-Holocene aridification triggered nonlinear settlement–hydroclimate responses characterized by threshold behavior, multi-centennial lags (∼0.5–1.5 kyr), and progressive Saharan abandonment with southward demographic shifts tracking north–south moisture gradients. Regional Random Forest models using expanding-window validation indicate moderate predictive skill (R² ≈ 0.47), suggesting structured but non-deterministic climatic influence on settlement intensity. Hidden Markov modeling identifies three recurring demographic regimes—expansion (16–6 kyr BP), transitional reorganization (6–4 kyr BP), and contraction after ∼4 kyr BP—consistent across most macro-regions and robust to alternative model specifications. These findings demonstrate a nonlinear and regionally asynchronous Holocene climate–human linkage driven by ecological thresholds, adaptive lags, and latitudinal gradients, with implications for understanding long-term climate vulnerability.