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Water Vapour CCI Project


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.

Latest news 

WV_cci Progress Meeting 7 (18 June 2020)

The consortium members called in to an extra Progress Meeting in June. The 2nd Annual Review meeting has been pushed back to after the summer, so PM7 was held to present and discuss recent progress.

Earlier news


University of Vigo joins the WV_cci team (13 May 2020)

The University of Vigo, Spain, has joined the climate research group (CRG) of the WV_cci consortium. The Vigo team will assess both total column and vertically resolved water vapour products in order to characterise the moisture profile and moisture transported by atmospheric rivers and low-level jets.

WV_cci at the Fall AGU Meeting, December 2019 (4 February 2020)

The WV_cci team were represented at the 2019 Fall AGU Meeting in San Francisco by DWD and Spectral Earth. Their poster titled, "Analysis of water vapour clear-sky bias from satellite observations" can be viewed below.

WV_cci Progress Meeting 6 (30 January 2020)

Following on from acceptance of the five updated deliverables after PM5, the WV_cci team called in to a PM6 teleconference on 30 January 2020 to review progress before the 2nd Annual Review in the spring.

WV_cci Progress Meeting 5 (21 November 2019)

The upcoming Progress Meeting at the University of Reading marks the half-way point of the WV_cci project! Team members will attend and present recent progress, which includes updates to five Phase One deliverables.

1st WV_cci Annual Review (19 June 2019)

The 1st Water_Vapour_cci Annual Review took place at ECSAT, Harwell, UK, on 19 June 2019. Most of the team were in attendance, giving presentations on achievements during the first year of the project. All Phase One deliverables have been submitted and were subsequently accepted.


8th G-VAP Workshop, AEMET, Madrid, Spain (13/14 June 2019)

The overall objective of the workshop was to discuss results from the various G-VAP science activities, to discuss results achieved within the wider community, including latest retrieval developments, to foster cooperation and exchange and to discuss the next steps of G-VAP, in particular potential new activities.

See GEWEX for more information.

Phase One Deliverables now available (February 2019)

Documents from Phase One of the WV_cci project are now available to view on the Resources section of this page. The documents are:

  • User Requirement Document (URD)
  • Product Specification Document (PSD)
  • Data Access Requirement Document (DARD)

User requirements collected (November 2018)

User requirements have been collected from interested parties in recent weeks.

Documents from the first 6 months of the WV_cci project are in progress, ready for the 2nd Progress Meeting, to be held 13-14 December 2018, at DWD, Offenbach.

The documents are:

  • User Requirement Document (URD)
  • Product Specification Document (PSD)
  • Data Access Requirement Document (DARD)

About the project

The Water_Vapour_cci project aims at four key deliverables, which include Climate Data Records (CDRs) of both total column water vapour over land and ocean (CDR-1 and CDR-2), and vertically resolved water vapour (CDR-3 and CDR-4, see Figure 1). These CDRs will work towards satisfying key user requirements of the climate research community that are defined at the beginning of the project and updated throughout the lifetime of the project. If you want to get involved in the user group of our water vapour products and help define climate data record requirements, please contact the science lead of Water_Vapour_cci. Below follow short descriptions of the different CDRs.

Figure 1: Key deliverables: The climate data records derived from a range of instruments will include both total column (TCWV) and vertically resolved (VRes WV) information on water vapour.
Key deliverables. The climate data records derived from a range of instruments will include both total column (TCWV) and vertically resolved (VRes WV) information on water vapour.













CDR-1: A total column water vapour CDR that will be based on near-infrared (NIR) observations from MERIS, MODIS, and OLCI. The ECV will be spanning the time period 2002 to 2017 with a spatial resolution envisaged to be of 0.05°/0.5° and as daily averages. Key challenges are to harmonise the time series due to issues around calibration performance, long-term stability and inconsistency between the single sensor records.

CDR-2:  CDR-1 will then be combined with ocean observations from microwave imager measurements (e.g., SSM/I and SSMIS) from EUMETSAT CM SAF. The combined product will span the time period 2002 to 2017 with a spatial resolution of 0.05°/0.5° and as daily averages. The combined product makes use of the spatial complementarities of the land based NIR and ocean based microwave observations without changing the characteristics of the original products. Thus, the combined product has global coverage and will be jointly released by Water_Vapour_cci and CM SAF. Key challenges are to fill coastal and ice covered areas and to achieve consistency between both products.

CDR-3: A vertically resolved water vapour CDR for the stratosphere will be merged using a range of ESA, third-party, and NASA instruments (including SAGE II, HALOE, POAM III, Odin SMR, MIPAS, SCIAMACHY, GOMOS, ACE-MAESTRO, ACE-FTS and Aura-MLS) and spanning the time period 1985 to the end of 2019. This database will have monthly time resolution and represent a zonal mean database.

CDR-4: A second vertically resolved water vapour CDR spanning the troposphere and the stratosphere and being resolved latitudinally, longitudinally, and monthly will be merged from a tropospheric product (i.e., the IASI-based IMS product) and several stratospheric products from still operating satellite limb sounders (Aura-MLS, ACE-FTS, ACE-MAESTRO). Key challenge is the merging across the tropopause, which is the interface between the troposphere and the stratosphere with very complex dynamical, physical, and chemical properties, greatly challenging the performance of EO instruments.

The derived CDRs will be validated and fully characterized by our validation team (Val) and then passed on to our climate research group (CRG) who will perform dedicated process and climate studies which aim at testing the usefulness of the new products and derive new knowledge related to the study of water vapour in the atmosphere. 

Resources, data and documents


Key Deliverables documentation:


The project team

The Water_Vapour_cci consortium is based on a close collaboration between the following partners including retrieval scientists (EO), data analysts (Val), system engineers (SysEng), and climate experts (CRG):

  • Michaela I. Hegglin (science lead, Val) and Hao Ye (University of Reading, UK)
  • Marc Schröder (science co-lead, CRG), Rainer Hollmann and Ulrike Falk (DWD, Germany) (CRG)
  • Kevin Halsall and Pauline Cocevar (Telespazio VEGA, UK)(project management)
  • Olaf Danne and Carsten Brockmann (Brockmann consult, Germany) (SysEng)
  • Rene Preusker and Juergen Fischer (Spectral Earth, Germany) (EO)
  • Richard Siddans and Brian Kerridge (STFC Rutherford Appleton Laboratory, UK) (EO)
  • Kaley Walker (University of Toronto, Canada) and Chris Sioris (ECCC, Canada) (EO)
  • Alexandra Laeng, Gabriele Stiller, and Thomas von Clarmann (KIT, Germany) (Val)
  • Tim Trent and John Remedios (University of Leicester, UK)(Val)
  • Daan Hubert and Jean Christophe Lambert (BIRA-IASB, Belgium) (CRG)
  • Helene Brogniez (University of Versailles, France) (CRG)
  • Luis Gimeno (University of Vigo, Spain) (CRG)


Contact us / support

Use the following emails to contact the Water Vapour_cci team:

  • General and technical support: pauline.cocevar[at]
  • Scientific leads: m.i.hegglin[at]; marc.schroeder[at]
  • Project manager: pauline.cocevar[at]
  • ESA technical officer: simon.pinnock[at]