Boundary-Layer Characterization Projects: USCRN

U.S. Climate Reference Network

Changes in the climate can influence economic prosperity, national security, and human and environmental health. Businesses, citizens, communities, governments, and international organizations are requiring accurate and high quality meteorological observations and forecasts to assess and adapt to current and potential threats associated with climate variability.

ARL has a long-term partnership with the NOAA National Centers for Environmental Information to operate and maintain the U.S. Climate Reference Network (USCRN). This network provides long-term robust climate observations that are necessary to document climate change trends for the United States. The USCRN provides high quality, reference-grade measurements of critical climate measures such as air temperature, precipitation, winds, land surface temperature, and solar radiation and translates that information for decision-makers to understand how and why climate has changed and what changes might occur in the future. ARL’s activities focus on:

  • advancing the quality and quantity of reference observations;
  • evaluating select observing systems for their ability to satisfy ongoing and evolving climate requirements;
  • improving the understanding of air-surface interactions; and
  • analyzing long-term observational datasets and models to understand climate variability and change.

ARL manages, operates, and maintains the 143 stations of the USCRN which includes 143 stations in the lower 48 (114); Alaska (25); Hawaii (2), and (2) in Canada. These stations provide long-term robust climate observations that are necessary to document climate change trends for the United States. The current plan is to extend the number of stations in Alaska to 29-30 by the end of fiscal year 2026. The network is now entering its third decade of service, having begun initial operations in 2002.

Researchers at ARL’s ATDD perform installation as well as extensive evaluation and maintenance of the array of instruments and the infrastructure for the USCRN. Additionally, ARL conducts energy, water, and greenhouse gas flux measurements and analyzes their relationships. A predictive understanding of the surface energy budget and related feedbacks is critical to the understanding of climate forcing factors at the land surface and the ability to credibly predict future conditions, especially those related to water resources.

ARL designs, evaluates, and maintains the array of instruments and the infrastructure for the USCRN to provide the Nation with a climate-quality benchmark observing system that meets national commitments to monitor the climate of the United States for the next 50-100 years. As a key participant in climate observing networks, both nationally and internationally, ARL develops methods for measuring climate parameters with high accuracy and reliability. The Lab also conducts long-term field studies to improve the understanding of interactions between the atmosphere, the land surface, and plants, which leads to better climate and weather predictions.

Wood fencing obscures an instrument on top of a mountain
Close-up of a USCRN station's precipitation gauge and wind shield. Credit: NOAA
Wood fencing obscures an instrument on top of a mountain
Close-up of a USCRN station's precipitation gauge and wind shield. Credit: NOAA
U.S. Climate Reference Network (USCRN) records an all-time USCRN maximum temperature was set on Sunday July 11, 2021 at the station in Stovepipe Wells, CA with a record of 128.6°Fahrenheit; that coupled with the highest ever daily minimum temperature recorded in North America of 107.7°F (and second most globally), resulted in the highest ever average daily temperature ever observed on the planet of 118.1°F as depicted in the hourly temperature profile,

Soil Moisture

Ten year range of soil moisture measurements for Merced, CA, as captured by USCRN data.

Soil moisture is a critical land surface variable as it impacts a range of climatological, agricultural, and hydrological processes. Soil moisture observations can forewarn of impending drought or flood conditions before other more standard indicators are triggered. These measurements are useful for applications ranging from agricultural monitoring to weather prediction, and from drought to flood forecasting.

Soil moisture data from the NOAA Air Resources Laboratory’s (ARL) is available on the US Climate Reference Network (USCRN) website as well as  through the redesigned US Drought Portal. The portal,, is hosted by NOAA’s National Integrated Drought Information System (NIDIS), was re-launched under a revised National Coordinated Soil Moisture Monitoring Network. The new network was designed to integrate soil moisture data from sources across federal and state in-situ networks, such as USCRN; remote sensing data; and other modeling capabilities.

Since 2008, NIDIS, ARL and the National Centers for Environmental Information (NCEI) have collaborated to install and manage not only the soil moisture sensors but also the data acquisition integration, data ingest, and quality control for soil observations at 11 out of the 114 sites in the CONUS. ARL installs and maintains USCRN, a network of 198 climate monitoring stations with sites across the continental US (CONUS), Alaska (23; with an eventual 29-30 sites), and Hawaii (2). These stations use high-quality instrumentation to measure the primary variables of air temperature, precipitation, wind speed, soil moisture and temperature (CONUS only), and other secondary variables such as ground temperature, solar radiation, and 1.5m level wind speed to ensure quality control of the primary measurements. The entire suite of quality controlled USCRN data, including soil moisture data, are also available via NOAA’s NCEI.

Soil moisture information is critical for weather and climate, runoff potential, flood control, soil erosion, prediction of crop yields, and reservoir management. Soil moisture plays an important role in the development of weather patterns and the production of precipitation. While there are other soil moisture networks, the USCRN is the only ground-based soil moisture network that spans the entire contiguous U.S. with a distribution of stations in nearly all the many different topographical, vegetation, and climate environments of the country.

Measuring Climate with the USCRN

Climate change is having wide ranging impacts to society and ecosystems globally. For example, climate change can alter rainfall, influence agricultural crop yields, affect human and animal health, cause changes to our oceans and forests, and even impact our energy supply. Environmental observations are fundamental to advance our understanding of how climate has changed, is changing, and will change in the future.

The U.S. Climate Reference Network (USCRN), developed by NOAA in the early 2000s, provides the Nation with long-term, high quality observations of air temperature, precipitation, and soil moisture and temperature collected in relatively stable and pristine environments. The USCRN’s measurements also provide critical anchor points for evaluating other observing networks, both public and private. Society and the economy benefit from the USCRN as its data are used in the decision support activities for a number of applications including weather warnings, water resource management, and reinsurance. Data are also used to improve both short- and long-term forecasts to protect lives and property.

In collaboration with NOAA’s National Centers for Environmental Information (NCEI), Air Resources Laboratory (ARL) researchers provide the overall management, engineering design and measurement capabilities and expertise for operating the USCRN stations, which includes the deployment and maintenance of the sites and regular calibration of the sensors. ARL also provides analysis of emerging sensor technologies for future applications. The near real-time and long-term archived data for all sites are served to the public by the NCEI. Unlike weather observing networks, USCRN was specifically designed with climate in mind, and the most unique feature is a triple sensor redundancy for air temperature, precipitation, and soil moisture and temperature, which is key in producing the highest quality climate data possible. The USCRN adheres to the Global Climate Observing System’s Climate Monitoring Principles as recommended by the National Research Council (NRC 1999)

Each station is strategically placed away from urban and suburban influences to avoid any possible locally-induced biases in the climate record. All of the stations in the contiguous U.S. are equipped with air temperature, precipitation, relative humidity (RH) sensors and soil moisture and temperature (the one exception being Torrey Canyon, Utah as it is built on solid rock). Soil sensors are installed in the Kenai, AK station, with research continuing on possibly extending these measurements into a more unique permafrost environment. Additionally, there are ancillary sensors measuring wind speed, solar radiation, ground temperature, and wetness to assist with the quality control of the primary air temperature and precipitation climate variables.

Station instruments on top of the mountain
USCRN station on Mauna Loa, Hawaii. Credit: NOAA
A metal grid structure surrounds a thin metal post, on top of which sits what looks like a metal bucket with a tapered top. Long, thin strips of metal hang in two circles, one inside the other, at the top of the structure, which is tethered to the ground by metal cables.
Rain gauge at a USCRN station. Credit: NOAA
Three pieces of monitoring equipment in a field
USCRN equipment at the University of Hawaii site in Hilo. Credit: NOAA Earth System Research Laboratory Global Monitoring Division


See the following reference for information about the status and assessment of the USCRN after 10 years of operation:

Diamond, H.J., T.R. Karl, M.A. Palecki, C.B. Baker, J.E. Bell, R.D. Leeper, D.R. Easterling, J.H. Lawrimore, T.P. Meyers, M.R. Helfert, G. Goodge, and P.W. Thorne, 2013: U.S. Climate Reference Network after one decade of operations: status and assessment. Bull. Amer. Meteor. Soc., 94(4); doi: 10.1175/BAMS-D-12-00170



Howard J. Diamond, PhD – USCRN Program Manager

National Oceanic and Atmospheric Administration
OAR/Air Resources Laboratory
NCWCP, R/ARL, Rm. 4215
5830 University Research Court
College Park, MD 20740