Refugees and IDPs fit into a global category of extremely structurally vulnerable people that are missing from standard poverty assessments, officially uncounted or uncountable using traditional census and survey methods . These include highly mobile populations, internally displaced by war and environmental hazards ; itinerant labourers; urban poor in informal settlements ; unauthorised migrants living in countries where they do not hold citizenship ; guest workers ; the homeless and institutionalised ; rural nomadic, pastoralist or landless populations ; and Indigenous Peoples and forest-dwelling communities . Frequently living without social safety nets, such as health care and formal education, these uncounted or 'missing millions' are vulnerable to problems associated with acute and chronic poverty, such as the spread of infectious disease and malnutrition . Because these 'missing' populations are not counted, they are frequently not a part of planning , including adaptation planning. In any particular national context, these missing populations may represent a small fraction of the population , however cumulatively hundreds of millions of people may be missing from official estimates . Over the last decade, techniques for estimating the locations, numbers and socioeconomic status of missing populations have moved beyond census and nationally representative household surveys, leveraging advances in satellite imagery  and data from mobile digital devices .
IPCC
Climate Change 2022: Impacts, Adaptation and Vulnerability
IPCC Report