Built-up area and population density: Two Essential Societal Variables to address climate hazard impact.

Area of Science:

• Earth and Environmental Sciences
• Human Geography
• Urban Planning

Background:

• Essential Climate Variables are used for climate modeling.
• Understanding human activities and their interaction with climate is crucial for risk assessment and policy-making.
• Existing datasets lack fine-grained global data on human settlements and population distribution.

Purpose of the Study:

• To introduce Essential Societal Variables (ESVs): global built-up area and population density.
• To provide data for modeling human activities and the impact of climate-induced hazards on society.
• To support policy-making, crisis management, risk assessment, and monitoring of Agenda 2030 goals.

Main Methods:

• Utilizing Earth observation image archives and national population census data.
• Developing global built-up area and population density layers within the Global Human Settlement Layer (GHSL) project.
• Producing data with fine granularity for multiple epochs (1975, 1990, 2000, 2015) with plans for regular updates.

Main Results:

• Generated global built-up area and population density layers for four distinct time periods.
• Demonstrated the relevance of ESVs for analyzing urbanization processes and assessing exposure to natural hazards.
• Provided examples of ESV application in policy-making and crisis management.

Conclusions:

• Essential Societal Variables offer a valuable complement to Essential Climate Variables for a holistic understanding of global change.
• ESVs are critical for informing policy decisions related to climate change adaptation, mitigation, and sustainable development.
• The GHSL project's data facilitates monitoring progress towards Sustainable Development Goals and enhancing disaster risk reduction strategies.