Abstract We present a new climatology of Martian water vapor column abundance derived from nadir dayside observations made by the Nadir and Occultation for MArs Discovery (NOMAD) instrument suite as part of the ExoMars Trace Gas Orbiter (TGO) mission. H 2 O vertical column densities are retrieved by applying an Optimal Estimation inversion scheme to the near‐infrared reflectance factor spectra acquired by the NOMAD Limb, Nadir and Occultation (LNO) channel over Martian Years 34–38 (April 2018–June 2025). By correcting for saturated absorption lines and using an improved Acousto‐Optical Tunable Filter (AOTF) calibration, H 2 O vertical columns retrieved from diffraction orders 167 and 169 quantitatively agree with co‐located MGS/TES (Thermal Emission Spectrometer) and EMM/EMIRS (Emirates Mars Infrared Spectrometer) independent observations, in terms of seasonal and latitudinal variations. A good agreement is also obtained with the GEM‐Mars General Circulation Model, except at high northern latitudes during the Aphelion season, where the current GEM‐Mars version underestimates the H 2 O summer peak. The geographical distribution of the retrieved H 2 O column abundances is characterized over the different Martian seasons and shows the typical patterns observed by previous space‐borne infrared instruments, such as the Pole‐to‐Pole transport and some local enhancements correlated with the topography. Our retrievals nevertheless indicate a more marked difference between Northern and Southern Hemisphere H 2 O column summer peaks. The seasonal cycle is also found to be stable from year‐to‐year, except during and after the Martian Year 34 global dust storm, where significantly smaller column abundances are observed compared to the same period in Martian Years 35–37.
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