Maintaining Irrigation Infrastructure Under Rising Climate Hazards: An Optimal Control Analysis of Financing Regimes with Reference to Vietnam

Irrigation networks in low-lying deltas are deteriorating faster than their design assumed, as salinity intrusion, floods and land subsidence add to ordinary wear. Whether they are kept in working order depends less on engineering than on how maintenance is financed and who decides when it is done. This paper builds a deterministic optimal control model in which a maintenance agency chooses the path of maintenance outlays to sustain the service capacity of an irrigation network whose deterioration rate rises with climate hazard intensity. Financing arrangements enter through two interpretable parameters: the social cost of one unit of maintenance funding and the discount rate applied by the deciding agency. The analysis is analytical and qualitative. We derive the steady state, the saddle-path dynamics and a complete table of comparative statics, and we state six propositions. Budget-cycle financing produces chronic under-maintenance, and the resulting gap separates cleanly into a financing component and a horizon component that call for different remedies. The horizon component widens as hazards intensify. Optimal maintenance spending is hump-shaped in the deterioration rate, and a short-sighted agency reaches the turning point, beyond which it lets the system contract, earlier than society would. The share of maintenance that farmers can afford to pay falls as hazards rise, a mechanism we call the climate squeeze on cost recovery. Finally, maintenance norms calibrated to historical deterioration erode capacity once hazards intensify. Read against Vietnam’s shift from irrigation fees to irrigation service prices, the results suggest that multi-year earmarked maintenance funds and affordability-capped prices are the main levers where hazards are moderate, while low-cost climate finance and planned transformation become decisive where hazards are severe.