Resilience Loss and Terrestrialization of the Ñeembucú Wetlands (Paraguay) Is Driven by a Climatic Pincer and Agricultural Expansion

Subtropical wetlands in the South American Chaco-Pampa transition are critical biodiversity reservoirs facing unprecedented thermal and hydric stress. Using a 39-year remote sensing time series (1985–2023), this study quantifies land-cover transitions and ecosystem resilience in the Ñeembucú Wetlands Complex, Paraguay. Our analysis reveals a severe degradation trajectory, marked by an 18.10% contraction of permanent wetlands. This decline is driven by compound hot and dry events acting as a “climatic pincer”—a strong negative spatial coupling between multi-decadal thermal anomalies and precipitation deficits (R = −0.60, p = 0.014). A synchronized ecological regime shift in 1999–2000 marked a transition to a warmer, low-frequency hydrological state, increasing drought phase duration by 73.5%. Post-1999, the ecosystem exhibited definitive Critical Slowing Down signals, with Lag-1 Autoregressive (AR1) coefficients surging to ρ = 0.85 (p < 0.001). Crucially, a sequential temporal lag was revealed: the hydro-climatic breakpoint initiated a climate-induced drying phase that created a ‘latent colonization window’ of accessible soils. This pre-weakened state subsequently facilitated aggressive mechanized agricultural encroachment nearly a decade later, locking the system into a degraded alternative state. To evaluate spatial risk, a binary logistic regression modeled terrestrialization probability as a function of the Martonne Aridity Index, confirming that aridity significantly amplifies wetland loss. Subsequent bivariate clustering categorized regional districts into distinct functional risk groups. These findings provide a robust predictive framework for understanding neotropical wetland collapse, highlighting the urgent need for proactive, resilience-based conservation.