The Solar Paradox: Pure Social Diffusion and Competitive Resource Capture in Semi-Arid Irrigated Land Expansion

Solar-powered irrigation is expanding rapidly across semi-arid regions, but the mechanisms through which this technology diffuses in informal groundwa- ter economies—where the majority of wells operate without permits—remain poorly understood. We address this gap through a spatiotemporal analysis of 3,201 solar wells identified via satellite census in Sidi Bouzid, Tunisia, combined with 10,000 control points. Cox proportional hazards models re- veal that terrain accessibility is the dominant spatial determinant: slope reduces the adoption hazard by 66% (HR = 0.339, p < 0.001), with prox- imity to urban centers (HR = 0.700) and lower elevation (HR = 0.718) also significant. Bass diffusion model estimation yields a near-zero innovation co- efficient (p = 0.001) alongside a high imitation coefficient (q = 0.679)—the first documented case of p ≈ 0 in agricultural technology diffusion, indicating a complete absence of institutional influence over the adoption process. We attribute this to a multi-layer governance failure in which legal barriers, fi- nancial exclusion, and extension collapse block all formal technology transfer channels. A neighbor effects model reveals that higher local adopter density slows subsequent adoption (HR = 0.606, p < 0.001), creating an apparent paradox with the high aggregate imitation. We reconcile this through a Com- petitive Diffusion Framework distinguishing an aggregate-level Information Effect from a local-level Congestion Effect linked to aquifer stress. The Fi- nance Law 2025’s pivot to retroactive regularization of unauthorized wells confirms that informal diffusion has outpaced regulatory capacity, marking a transition from administrative exclusion to fiscal capture in Tunisia’s ground- water governance.