Emerging climate–yield re-coupling in overexploited date palm oases: satellite evidence from a 22-year temporal decoupling index in southern Tunisia

Tarek Gasmi , Ramzi Guesmi, Slim Ben Abdelbari, Soura Boulaares, Sajeda Albarghati

Southern Tunisia's date palm oases have quadrupled production over two decades while extracting fossil groundwater at more than twice the sustainable rate, a trajectory whose consequences remain undetected by conventional monitoring. We analysed the 2002–2024 satellite, climate, and ground record across four governorates to test whether this irrigation buffer — the aquifer's capacity to absorb climate variability on behalf of the crop — is still intact or already degrading.

The buffer is still largely effective: no satellite or climate covariate carries a learnable signal about interannual yield anomalies, and every model we tested performs worse than a naive trend baseline. But the resource sustaining that buffer is disappearing. GRACE/GRACE-FO terrestrial water storage has declined by 16.6 cm since 2002, with the aquifer approximately stable through the mid-2000s and then declining at roughly 1 cm per year. And in Kébili, the governorate with the most overexploited aquifer (229% of renewable resources), the buffer is already cracking: per-hectare yield has become progressively more sensitive to vapour pressure deficit over the study period (HAC-corrected p < 0.001), a signal that strengthens after area normalisation (Δ|r| = +0.444) and is robust to detrending method and placebo-feature tests, though it emerges from an exploratory scan and does not survive FDR correction in the full grid. Tozeur shows a similar pattern; Gafsa's signal is tentative.

In these oases, satellite monitoring detected the onset of buffer degradation years before any decline appeared in the production record, suggesting that the primary value of earth observation in aquifer-dependent agriculture lies in tracking buffer integrity rather than predicting yields.