Effects of drought on soil moisture and water resources in Hawaiʻi

A large tree borders a view looking upslope across a dry grassy landscape.
Changes to water availability in forests and open grasslands are important to investigate if managers are to have a fighting chance to cope with future climatic changes. (Photo: AMair)

Droughts in the Hawaiian Islands can enhance wildfire risk, diminish freshwater resources, and devastate threatened and endangered species on land and in nearshore ecosystems. During periods of drought, cloud-water interception, or fog drip (the process by which water droplets accumulate on the leaves and branches of plants and then drip to the ground) in Hawai‘i’s rain forests may play an important role in providing moisture for plants, reducing wildfire risk within the fog zone, and contributing to groundwater recharge (the process by which water moves downward from the surface through the ground to the groundwater table) that sustains water flow in streams during dry periods. Estimates of the changes in water availability during periods of drought are critical to Hawai‘i’s water, forest, and wildfire managers and planners, as well as to agriculturists and ranchers for developing adaptive management strategies.

This study addresses this specific information need and will lead to a better understanding of the hydrologic impacts of drought throughout the State of Hawai‘i. Specific objectives of the study are (1) to estimate changes in soil moisture, evapotranspiration, and groundwater recharge during periods of drought for current and projected climate conditions, and (2) to estimate the combined impact of drought and reduced fog drip on soil moisture, evapotranspiration, and groundwater recharge.

The results from this study will inform resource managers of the potential impacts of climate change on water resources and the importance of fog drip in mitigating the impacts of drought. This study will also provide needed input for supporting science-based strategies for managing critical groundwater recharge areas and identifying areas vulnerable to wildfires. The results will be a great value to forest and water-resource managers, watershed partnerships striving to protect, preserve, and restore large areas of forested watersheds for water-resource and conservation values, and outreach agents seeking to reduce the threat of wildfire to ecosystems and communities by facilitating the sharing of fire knowledge.





Alan Mair
Hydrologist, USGS Pacific Islands Water Science Center