Climate and Management Effects on Soil Infiltration and Runoff in Hawaiian Forests

Science Center Objects

Hawai‘i's precipitation is greatest in upland areas that are typically forested. This precipitation provides water for both people and ecosystems. Precipitation can either run off and contribute to streamflow, or infiltrate into the ground and provide water for plants, base flow to streams, or recharge to aquifers. The exact routing that water takes is controlled by many factors, including the duration and intensity of rain, topography, soil properties, and vegetation. The objective of this project is to understand how climate change and invasive species affect the potential infiltration of rain into aquifers.

Overview:

Movie of water level dropping in an infiltrometer used to measure water infiltration into the soil

Water level changing in an infiltrometer used to measure the rate of water infiltration into the soil. Infiltration rates were measured across forest sites in Hawai‘i. The red coloring was used at some sites where infiltration was slow enough that camera systems were used to log the rate of water level drop over time. In those automated measurements, the red food-grade dye made identification of the water level from digital images easier.

(Credit: Lucas Fortini, USGS - PIERC. Public domain.)

Hawaii's precipitation is greatest in upland areas that are typically forested. This precipitation provides water for both people and ecosystems. Precipitation can either run off and contribute to streamflow, or infiltrate into the ground and provide water for plants, base flow to streams, or recharge to aquifers. The exact routing that water takes is controlled by many factors, including the duration and intensity of rain, topography, soil properties, and vegetation.  The role of vegetation in the water cycle is multifaceted. In addition to transpiration, vegetation intercepts rainfall and cloud water, altering the flow of water from the top of the canopy to the ground. Vegetation can also affect the infiltration properties of soil. These changes can alter the routing of water, and thus establish a feedback between the vegetation ecology and watershed hydrology. Limited existing research indicates that native and invasive plant species may cause different hydrological responses. However, these responses generally are poorly understood and quantified.  In Hawaii, increased demand and competition for limited water resources has highlighted the need for better information on and understanding of how human and natural factors affect water availability. Population growth, climate change, and the increasing value attributed to ecosystem services (environmental processes that produce resources) call for a better understanding of the relation between forests and water resources. Models that simulate the flow of both surface water and groundwater through a watershed are emerging tools for water-resource management. However, statewide measurements of relevant soil properties that affect runoff and recharge, and a broad understanding of how forest composition and structure affect those properties are lacking. Existing information from Natural Resources Conservation Service (NRCS) datasets are valuable but are insufficient to evaluate the effect of vegetation type on runoff and recharge.

Objectives:

The objective of this project is to understand how climate change and invasive species affect the potential infiltration of rain into aquifers. We will used a geospatial framework to understand how geologic, ecologic, and climatic features influence the infiltration capacity of soils that underlie forests so that impacts from invasive species and climate change can be understood.

Study Area:

Across closed canopy ohia/koa forests in wet and mesic areas of the island of Hawai‘i and Kaua‘i.

 

Field crew gathered for a photograph in the forest

Field crew ready for data collection on soil infiltration rates of water in forests on the island of Kaua‘i.

(Credit: Kai‘ena Bishaw, Hawai‘i Cooperative Studies Unit. Public domain.)