Water Resources Research Act Program

Details for Project ID 2008HI224B

Improving Water Resource Assessment in Hawai`i by Using LiDAR Measurements of Canopy Structure to Estimate Rainfall Interception

Institute: Hawaii
Year Established: 2008 Start Date: 2008-03-01 End Date: 2010-02-28
Total Federal Funds: $20,987 Total Non-Federal Funds: $43,242

Principal Investigators: Thomas Giambelluca

Project Summary: Water resources in Hawaii continue to experience increasing demand, putting pressure on existing sources and increasing the need for better estimates of resource capacity (Oki 2002). For ground-water sources, in particular, reliable estimates of sustainable yield limits are critically important. Groundwater recharge estimates, in turn, are needed to determine accurate safe yield limits. Recharge is highly spatially variable in Hawaii (Giambelluca 1983), because of extreme gradients in precipitation and evapotranspiration (ET). The accuracy of recharge estimates in Hawaii has been limited by a lack of direct measurements of ET within forested recharge areas. Recent research has improved our knowledge of stand-level ET in Hawaii and pointed to the need to better understand interception loss, the amount of rainfall intercepted by leaves and stems and subsequently evaporated (Giambelluca et al. in prep.). The amount of interception loss, which can vary from 10 to 50% of incoming precipitation (Roth et al. 2007), is strongly influenced by canopy structure, especially canopy gap fraction, leaf, stem and epiphyte storage capacity, and branch angle (Rutter et al. 1975; Gash 1995), and, hence, is highly variable across the forested landscape. Alien trees, some of whichsuch as Psidium cattleianum (strawberry guava)are highly invasive, are markedly different in structure from native trees, such as Metrosideros polymorpha (ohia). Very little is known about the rate and spatial variability of interception loss and the effects of alien tree introductions on interception in Hawaii. The traditional method for measuring interception, based on canopy water balance, is difficult and very limited in spatial coverage. But, recent advances in ground-based and airborne LiDAR technology offer the promise of spatially-distributed estimates of interception using a physically-based approach (Roth et al. 2007). The objective of this project is to utilize a newly-acquired LiDAR system and existing state-of-the-art field measurement facilities to develop and test a new method for estimating interception in Hawaiis native and invaded forests.