Book Description

Land use plays an integral role in the water cycle because human impact on land cover directly affects water resources and other ecosystem processes on both short and long time scales. When these impacts are quantified, it may be possible for water users to enhance their water resources by compensating upstream land owners for specific land-management actions. In this dissertation, I consider the effects of land cover on water resources through the framework of hydrologic ecosystem services and consider the synergies and tradeoffs in managing for the quantity, quality, location, and timing of available water as well as for other ecosystem services. In many water-limited environments, increasing groundwater recharge is a primary consideration in watershed management. The Kona area on the leeward side of Hawai'i Island, where rainfall on the mountain slopes is the sole source of water for coastal communities, provides a useful case study. A water balance approach is used to determine the influences of vegetation on recharge. Over 18 months, from the summer of 2006 through the winter of 2008, I measured precipitation, including rainfall and cloud interception, and modeled evapotranspiration, using a Penman-Monteith model based on hourly meteorological measurements and direct measurements of stomatal resistance and stem water potential. There is no runoff in these highly permeable basalt watersheds, simplifying fluxes in and out. The recharge to rainfall ratio at these sites is close to one. Differences in recharge between vegetation types are due largely to direct interception of cloud water by native Hawaiian forest, as the unusual combination of relatively high radiation and low vapor pressure deficit in conjunction with lack of water stress causes evapotranspiration at all sites to be low. Precipitation influxes are heavily weighted by infrequent, large storms. I quantify the effects of land-use change on pumping expenses to the downstream community and weigh the private costs and benefits of land use change against the public costs and benefits as translated by avoided or additional costs to the water utility. Conversion of pasture land to plantation forest is potentially lucrative for the landowner, but it decreases recharge and thus carries public costs. The magnitude of the private benefits and public costs are similar, so a direct financial transaction between the utility and the landowner may be possible to improve overall welfare. Costs of conversion from open to dense forest carry much greater costs for the landowner than hydrologic benefits, but in this case non-monetary public benefits such as carbon sequestration, habitat for biodiversity, and non-timber forest goods are aligned with the hydrologic benefits and the full suite of benefits may have a large enough value to offset the costs and allow this conversion to go forward. This dissertation is unique in tying together a rigorous biophysical assessment with an economic analysis of both the costs and benefits of providing a hydrologic service. In so doing, it demonstrates a thorough hydrologic services assessment, providing a model for future ecosystem service assessments in Kona and elsewhere.