Monthly Water-Budget Components for Roi-Namur, Kwajalein Atoll, Republic of the Marshall Islands, 2000-12

The zipped folder (Monthly_water_budget_Roi-Namur_2000-12.zip) associated with this metadata file contains 156 polygon shapefiles. Collectively, the 156 shapefiles contain spatially distributed estimates of groundwater recharge and other water-budget components, in inches, for Roi-Namur, Kwajalein Atoll, Republic of the Marshall Islands, for each month and year during 2000–12. The name of each shapefile indicates the year and month of the water-budget components contained in the shapefile.

The month-year estimates of recharge and other water-budget components summarized in each shapefile were summed from daily water-budget components that were computed using a water-budget model. The equations of the water-budget model that we used for Roi-Namur were the same as those (equations 1–16) described in Johnson and others (2014). Johnson and others (2014), available at (https://pubs.usgs.gov/sir/2014/5168/) and hereinafter U.S. Geological Survey Scientific Investigations Report (USGS SIR) 2014-5168, describes a water-budget model used for the island of Maui, Hawaii. In USGS SIR 2014-5168, the “Conceptual Model” section has a general description of the water-budget model, and the “Model Calculations” section has a detailed description of the equations and variables used in the model. Several water-budget components considered in the Hawaii water-budget model described in USGS SIR 2014-5168 were excluded from the water-budget model for Roi-Namur. Fog interception and irrigation were excluded because they were assumed to be negligible. Water leakage from water-storage tanks was excluded because leakage rates were not known (Chugach Management Services, Inc., written communication, 2014). Water leakage from the rain water-catchment basins and water-transmission systems also was excluded. According to a soil database published by the U.S. Department of Agriculture, Natural Resources Conservation Service (2014), soils on islands of nearby atolls (Maloelap, Aur, Majuro, Arno, and Mili) have “very low to negligible runoff.” Although this soil database does not have soil information for islands of Kwajalein Atoll, we assumed soil properties for Roi-Namur were similar to those on islands of nearby atolls. Therefore, runoff to the ocean from all surfaces was excluded because it was assumed to be negligible owing to the island’s porous soil. Runoff from impervious surfaces, however, was quantified in the model as “excess water” that was assumed to either be captured by catchment systems for storage or flow to pervious surfaces.

This abstract and the attribute definitions in this metadata file have descriptions of the input data we used in the model for Roi-Namur. Prior to computing recharge, we subdivided the island of Roi-Namur into 68 polygons, which we refer to as subareas, and which are represented in each shapefile. An explanation of the methods used to create the subareas is included in this metadata file in the description for the Subarea_ID attribute. The water-budget model computed daily groundwater recharge and other water-budget components separately for each of the 68 subareas. The attributes associated with each polygon include monthly estimates of rainfall, forest-canopy evaporation, rain water captured from the airport runway, surplus rainfall-catchment water discharged to the ground near the airport runway, potential evapotranspiration, actual evapotranspiration, total evapotranspiration, natural recharge from rainfall, artificial recharge from surplus rainfall-catchment water, and total recharge. For each attribute, this metadata file includes a description of how it was estimated in the water-budget model.