WaterSip is a diagnostic software tool that identifies the evaporation sources and transport pathways of precipitation or water vapour over a target area based on Lagrangian model output. In addition to the geographic location, WaterSip identifies select thermodynamic properties of the moisture sources, during atmospheric transport, and during arrival over the target area. WaterSip software thereby employs the Lagrangian diagnostic algorithm for quantitative moisture source accounting of Sodemann et al. (2008b). The software tool requires output from Lagrangian particle dispersion models or trajectory models as input for the diagnostic. Moisture sources are then identified from changes in specific humidity along these trajectories at each output time step. The ratio between changes in specific humidity and the specific humidity of the air parcel allow to estimate the quantitative contribution of a moisture source to the air parcel at a specific time and location. Together with the temporal sequence, this provides the basis for identifying moisture source contributions to the final precipitation. WaterSip also identifies and aggregates further thermodynamic and geographic properties of the moisture source and during the moisture transport. Designed to operate on large datasets of regional to global domain-filling trajectories, WaterSip provides the results of the moisture source identification as gridded information in a variety of output files in netCDF format. This paper describes the relevant methodological foundations, the technical set-up and configuration, and provides a consistent example case study to illustrate the use and interpretation of the software tool and its results. Importantly, key uncertainties and caveats are described and discussed throughout the text. Users of WaterSip should be aware of these uncertainties to obtain a valid and reliable interpretation of the diagnostic results.
Reference publication
Sodemann, H.: The Lagrangian moisture source and transport diagnostic WaterSip V3.2, EGUsphere [preprint], https://doi.org/10.5194/egusphere-2025-574, 2025.
Software repository
The WaterSip source code is hosted at https://git.app.uib.no/GFI-public/watersip.
Associated datasets
Sodemann, H. (2025). Source code of the Lagrangian moisture source and transport diagnostic WaterSip V3.2.1 (v3.2.1b). Zenodo. https://doi.org/10.5281/zenodo.17360464
Sodemann, H. (2025). Particle position output from the FLEXPART dispersion model for a test case for use with the WaterSip moisture source diagnostic (2.0.1) [Data set]. Zenodo. https://doi.org/10.5281/zenodo.16813429