Water vapour (H₂O) in the atmosphere is a key component of the Earth’s hydrological cycle, critical in shaping the global environment and supporting life on Earth as we know it. Manifold physical processes thereby help redistributing the water from the oceans to the land involving the formation of clouds, precipitation, and extreme weather events. Water vapour also has a key role in constraining the Earth’s energy balance. It is the single most important natural greenhouse gas in the atmosphere and constitutes a strong positive feedback to anthropogenic climate forcing from carbon dioxide (CO₂). The water vapour feedback is critically important in understanding past and determining future climate change and its global and regional impacts. It is due to its importance, that GCOS has identified water vapour as an essential climate variable (ECV). However, the properties of the Earth’s atmospheric water vapour distribution challenge not only climate research, but also Earth Observation science, from instrument development to retrieval science. ESA’s Water_Vapour_cci project will help to consolidate our knowledge of past changes as derived from observations and to establish climate data records for use in climate research. 

The ultimate objective of the Water_Vapour_cci is to generate new global high-quality climate data records of both total column and vertically resolved water vapour, which are homogeneous in space and time, work towards fulfilling GCOS requirements, and respond to the user needs of the climate research community in the best possible way.  

At the same time, Water Vapour_cci will optimise the temporal and spatial resolution of these climate data records with respect to the assessed limitations of available observing systems and quantify uncertainties that are useful to the end users. Water Vapour_cci will also analyze climate variability and trends in atmospheric water vapour on different spatial and temporal scales, and consistency between observations and theoretical expectations using comparisons to ERA5 and climate models in the CMIP context, in order to advance our scientific understanding of the importance of water vapour in the climate system and to support climate services such as C3S.

The contribution of KIT is the validation of the level-2 vertically resolved stratospheric data records of the individual participating instruments. The data records are provided in the data format used within all CCIs (WP2.6).

Water vapour profiles from WAVAS SAtellite component in HARmonized format (WAVAS_SAHAR) - Version 2