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

Tarek Gasmi, Ramzi Guesmi, Slim Ben Abdelbari, Ghaith Hammami

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.