WWAP introduced the WWDR 2021 by building on the condensed literature review (Annex 2), the draft ‘storyline’ (Annex 3), and an initial compilation of potential ‘main messages’ (Annex 4). These background documents prepared by WWAP constituted the discussion material for the workshop by describing the theme and scope of the WWDR 2021, highlighting technical considerations and illustrating sources of information.