Groundwater recharge estimates for the United States part of the Salish Sea Basin, northwestern Washington

This data release documents estimates of groundwater recharge for the U.S. portion of the Salish Sea Basin in northwestern Washington. A U.S. Geological Survey Soil-Water-Balance (SWB) model (Westenbroek and others,2018) was developed for Hydrologic Unit Code 17110 to simulate the spatial distribution of net infiltration below the root zone on a daily time step from January 1, 1980, through December 31, 2020. As with all numerical models, the SWB model output has uncertainties. Hydrologic numerical models exhibit inherent uncertainty arising from input datasets, model structure, calibration parameters, and the scenarios being simulated (Singh and others, 2024). For example, the unsaturated zone between the root zone and the water table is not simulated in the SWB model, which may contribute to differences between simulated net infiltration and the amount of water that ultimately reaches the water table (Westenbroek and others, 2018). When the water table is at the land surface, calculated net infiltration cannot enter groundwater that is already saturated. To address these issues and other model uncertainty, a bias-correction process was implemented to adjust SWB net-infiltration to be consistent with groundwater budget constraints.

This data release includes three child items:

A. "Uncorrected Soil-Water-Balance model for the United States part of the Salish Sea Basin, northwestern Washington" - This child item contains model documentation and all SWB model input and output files.

B. "Bias correction method for the Soil-Water-Balance model output for the United States part of the Salish Sea Basin, northwestern Washington" - This child item includes files related to the bias correction process, including a detailed readme file outlining the methods and the final bias correction surface.

C. "Bias corrected Soil-Water-Balance model output for the United States part of the Salish Sea Basin, northwestern Washington" - This child item provides final annual average recharge estimates for 2011–2020 derived from bias-corrected SWB model output.

References:

Singh, V.P., Singh, R., Paul, P.K., Bisht, D.S., and Gaur, S., eds., 2024, Hydrological processes modelling and data analysis: A primer: Singapore, Springer Nature Singapore, 285 p.

Westenbroek, S.M., Engott, J.A., Kelson, V.A., and Hunt, R.J., 2018, SWB Version 2.0 - A soil-water-balance code for estimating net infiltration and other water-budget components: U.S. Geological Survey Techniques and Methods, book 6, chap. A59, 118 p., https://doi.org/10.3133/tm6A59.