Linking water-balance simulation and multiobjective programming: land-use plan design in Hawaii

In the Hawaiian Islands, planners and public officials have decided recently to raise the permissible level of urban development in central Oahu. The decision is opposed by many on the grounds that it threatens agricultural land as well as the sustainability of groundwater supply. A two-part procedure is presented for exploring the impacts of such development and designing urban-expansion patterns that minimize them. First, a water-balance simulation model is used to calculate groundwater recharge as it varies with land use and location within the area. The difference between recharge and withdrawal is computed, and any changes are then estimated for different land uses. This information is then incorporated into optimization models having objectives related to agricultural land retention, groundwater balance, and residential population growth. The models generate alternative land-use expansion plans and show the trade-offs among objectives. The consideration of slightly suboptimal (dominated) solutions allows a significant expansion in the range of such alternatives. The results suggest that, if future agricultural development does not occur on currently nonagricultural land, then both agricultural land and groundwater sustainability will suffer significant adverse effects under the new population limits.