Population - WITNESS

Population is an endogenous model in WITNESS. The model is based on McIsaac (2017)1  with some modifications. First, the model is run on a one year time step instead of a five year time. Then, the population is divided in one year age groups instead of five year age range groups. Lastly, the birth rate equation has been modified by adding the influence of education on the number of children.

• Population dynamicThe population is divided in one year age-range from 0 to 100+ year old, with each year the population gets one year older. There is an amount of newborns that will represent the 0 age range, and there is also a certain amount of deaths per age category.
• Birth rateAccording to the United Nation definition, the age-specific birth rate is the "number of births to women in a particular age group, divided by the number of women in that age group". In our model, we look at the birth rate for the 15-49 age group, the young active population in childbearing age. The birth rate depends on Gross World Product, population and knowledge
• Death rateThe death rate is the number of deaths divided by the number of persons in a specific age category and year. Similarly to birth rate, the death rate per age category and year depends on Gross World Product and on population. Death rate is also impacted by climate in four principal ways, global warming affects crops by reducing yields and the micro/macronutrients contents of cereals, favors allergens and vector-borne infectious diseases such as malaria or dengue, increases risks of diarrheal diseases due to heat waves causing reduced access to safe water, and increases probability of heat waves that causes higher mortality related to cardiovascular or chronic respiratory diseases³. It is modelized following excess mortality function associated with climate change
• Working age populationThe working age population is the population in age to work, it is the sum of population in the 15-70 age range. It's used by macro-economy to define labor capability together with education
• Life expectancyLife expectancy at birth is the age-averaged proportion of surviving people, which is depending on GDP per capita.

For more informations, please see detailed specific documentation

Note: The documentation of WITNESS is 'in preparation' and is not yet 'published'!

Model Documentation - WITNESS
Appendices - WITNESS Mathematical model description - WITNESS Data - WITNESS References - WITNESS
Corresponding documentation
AIM-Hub BLUES C3IAM COFFEE-TEA DNE21+ GCAM GEM-E3 GRACE IFs IMACLIM IMAGE MESSAGE-GLOBIOM POLES PROMETHEUS REMIND-MAgPIE TIAM-UCL WITCH COFFEE-TEA
Previous versions
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Model information
Model link	https://www.witness4climate.org/world-environmental-impact-and-economics-scenarios/
Institution	Open-Source for Climate (OS-C), N/A, https://os-climate.org/transition-analysis/., Linux Foundation (LF), N/A, https://www.linuxfoundation.org/.
Solution concept	Systems dynamics based approach
Solution method	OptimizationSimulation-based optimization
Anticipation