DOI: 10.5066/p9zacz6h
title: Long-term monotonic trends in annual groundwater metrics in the United States through 2020 (ver. 3.0, September 2025)

description: The U.S. Geological Survey (USGS) Water Resources Mission Area (WMA) is working to address a need to understand where the Nation is experiencing water shortages or surpluses relative to the demand by delivering routine assessments of water supply and demand. A key part of these national assessments is identifying long-term trends in water availability, including groundwater and surface water quantity, quality, and use.  This data release contains Mann-Kendall monotonic trend analyses for annual groundwater metrics at 54,932 wells located in the conterminous United States, Alaska, Hawaii, and Puerto Rico.

The groundwater metrics include annual mean, maximum, and minimum water level and the timing of the annual maximum and minimum groundwater level. These metrics are computed from groundwater water levels from publicly available data from the National Water Information System (NWIS), the National Groundwater Monitoring Network (NGWMN) and the California Open Data Portal. Trend analyses are computed using annual groundwater metrics through the water year, which is defined as the 12-month period October 1, for any given year through September 30 of the following year  (for example, October 2019 through September 2020). Trends at each well are available for up to four different periods: i) the longest possible period that meets completeness criteria at each well, (ii) 1980-2020, (iii) 1990-2020, (iv) 2000-2020.

Annual mean, maximum, and minimum water-level metrics for wells screened in unconfined aquifers were determined only when a well's water-level time series was at least 70 percent complete.  Additionally, each of these time series must have at least 70 percent complete records in the first and last decade.  All longest possible period time series for wells in unconfined aquifer must be at least 10 years long and have annual metric values calculated for at least 70% of the years of the record.  Annual mean, maximum, and minimum water-level metrics for wells screened in confined aquifers were determined only when a well's water-level time series was at least 50 percent complete.  Additionally, each of these time series must have at least 50 percent complete records in the first and last decade.  All longest possible period time series for wells in confined aquifer must be at least 10 years long and have annual metric values calculated for at least 50% of the years in the last 10 years of the record.

Caution must be exercised when utilizing monotonic trend analyses conducted over periods of up to several decades (and in some places longer ones) due to the potential for confounding deterministic gradual trends with multi-decadal climatic fluctuations.

This data release contains:
six input files:
NGWMN_gwl_meta_v3.0.csv, the metadata from the National Groundwater Monitoring Network
NGWMN_gwl_data_v3.0.csv, the groundwater water level data from the National Groundwater Monitoring Network
NWIS_gwl_meta_v3.0.csv, the metadata from the National Water Information System
NWIS_gwl_data_v3.0.csv, the groundwater water level data from the National Water Information System
CA_measurements_v3.0.csv, the groundwater level data from the California Open Data Portal
CA_stations_v3.0.csv, the groundwater metadata from the California Open Data Portal

three output files:
GW_trendsout_v3.0.csv, the groundwater water level trend data from both the National Groundwater Monitoring Network and the National Water Information System  
GW_conf_bands_out_v3.0.csv, the confidence bands associated with the groundwater water level trend data from both the National Monitoring Network and the National Water Information System
GW_annual_mean_v3.0.csv

A .zip file containing all of the code used to compute these trends along with a README file with information on using the code


First posted - Feb 27, 2024 (available from author)
Revised - Jan 30, 2025 (version 2.0) (available from author)
Revised - September 22, 2025 (version 3.0)