The International Soil Moisture Network (ISMN): A data service providing free access to in situ observations

Soil moisture is a key variable impacting land–atmosphere interactions, hydrological extremes, ecosystem processes, and agricultural productivity among others. Reliable in situ observations are essential for understanding soil moisture dynamics and for evaluating satellite-based products and land surface models. However, ground-based soil moisture measurements are often scattered across independent networks and remain difficult to access in a harmonized form. The International Soil Moisture Network (ISMN) was established to overcome these limitations by providing a global, freely-accessible repository of quality-controlled in situ soil moisture observations. Its mission is to support Earth system science, remote sensing validation, and model development through standardized and traceable soil moisture data.

The ISMN collects soil moisture time series from a wide range of regional, national, and international monitoring networks. Contributing datasets are harmonized in terms of format, metadata, and temporal resolution and undergo a consistent quality control procedure. The database includes multi-depth measurements across diverse climates, land cover types, and soil conditions, complemented by ancillary site information. Data are distributed through a dedicated web interface (https://ismn.earth), enabling efficient data discovery and use for large-scale and local studies.

Ongoing efforts are focusing on expanding the database by incorporating additional stations and data providers from institutional or governmental sources, as well as enhancing data quality and consistency to support more robust long-term analyses. Further resources are directed towards fortifying the operational system and improve usability to better serve our users. Beyond research applications, the ISMN increasingly contributes to the data-to-value chain of international initiatives that are led by the World Meteorological Organization (WMO), the Food and Agriculture Organization (FAO), and the Global Climate Observing System (GCOS). One example is the contribution of ISMN data to WMO’s annual State of the Global Water Resources report, supporting global assessments of hydrological conditions.