DOI: 10.5066/p9hghws4
title: Frequency characteristics of soil moisture, evapotranspiration, and climatic water deficit for Kauaʻi, Oʻahu, Molokaʻi, Maui, and the Island of Hawaiʻi, for a set of rainfall and land-cover conditions

description: These shapefiles represent the frequency characteristics of soil moisture, evapotranspiration, and climatic water deficit for Kauaʻi, Oʻahu, Molokaʻi, Maui, and the Island of Hawaiʻi for a set of water-budget scenarios that characterize unique combinations of rainfall and land-cover conditions. Four water-budget scenarios were developed to quantify the effects of drought on soil moisture, evapotranspiration, and climatic water deficit for each island as follows: (1) a reference condition, the Non-Drought scenario, consisting of rainfall conditions during 1990–97 and 2003–06 and 2020 land cover, (2) rainfall conditions representative of the driest periods during 1920–2012 and 2020 land cover, (3) rainfall conditions representative of non-drought conditions during a future dry-climate condition and 2020 land cover, and (4) rainfall conditions representative of the driest periods during a future dry-climate condition and 2020 land cover. For Oʻahu, Maui, and the Island of Hawaiʻi, a total of six additional water-budget scenarios were developed to quantify the added effects of drought and reduced cloud-water interception on soil moisture, evapotranspiration, and climatic water deficit as follows: (1) rainfall conditions representative of the driest periods during 1920–2012 and Conversion 1 land cover, (2) rainfall conditions representative of the driest periods during 1920–2012 and Conversion 2 land cover, (3) rainfall conditions representative of non-drought conditions during a future dry-climate condition and Conversion 1 land cover, (4) rainfall conditions representative of non-drought conditions during a future dry-climate condition and Conversion 2 land cover, (5) rainfall conditions representative of the driest periods during a future dry-climate condition and Conversion 1 land cover, and (6) rainfall conditions representative of the driest periods during a future dry-climate condition and Conversion 2 land cover. The future dry-climate condition is a Representative Concentration Pathway projection during 2071–99 with a total radiative forcing of 8.5 Watts per square meter by the year 2100 (RCP8.5 2071–99 projection) described in Elison Timm and others (2015). Conversion 1 land cover is a hypothetical land-cover condition in which roughly 50 percent of shrubland and forest areas within the cloud zone are converted to grassland, for which cloud-water interception is considered to be negligible. Conversion 2 land cover is a hypothetical land-cover condition in which 100 percent of shrubland and forest areas within the cloud zone are converted to grassland.
 
Monthly time series estimates of soil moisture, evapotranspiration, and climatic water deficit for each model subarea were computed for each scenario using the water-budget code known as WATRMod, a Water-budget Accounting for Tropical Regions Model (Oki, 2022). Monthly time series estimates of soil moisture, evapotranspiration, and climatic water deficit were used to compute the relative frequency for each model subarea for selected moisture-stress levels, where relative frequency describes the decimal fraction of months that soil moisture or evapotranspiration is less than or equal to (or climatic water deficit is greater than or equal to) the selected moisture-stress levels. A value of 0.074 was selected as the moisture-stress level for monthly mean soil moisture, expressed as a fraction of available water capacity. A value of 0.96 inches was selected as the moisture-stress level for monthly evapotranspiration. Climatic water deficit is defined as the evaporative demand that exceeds available water and is calculated as the difference between potential evapotranspiration and evapotranspiration. A value of 0.77 was selected for monthly climatic water deficit, expressed as a fraction of potential evapotranspiration.
 
The shapefile attribute information associated with each subarea present an estimate of the relative frequency of soil moisture, evapotranspiration, and climatic water deficit for each drought scenario, and select geographic and land-cover attributes. Brief descriptions of the relative frequencies and other attributes are included in this metadata file. Refer to Mair and others (2024) for further details of the methods and sources used to select the moisture-stress levels and determine the relative frequencies of soil moisture, evapotranspiration, and climatic water deficit, and characterize the other attributes.