Agent-based simulation of the spatial evolution of the historical population in China

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  • 1. Jing Wu, Zheng Wang Institute of Policy&Management, Chinese Academy of Sciences 09/01/09
  • 2.
    • The origin of Chinese population is in the Yellow River basin, but now people resident all over China. What’s the main driving force that makes people move around ?
    • The population in North China exceeded that in south in early ancient times, but the pattern reversed with more population in south less in north nowadays. Why? When did it happen?
    • 94.4% of the total population lives in the east, occupying 36% of the total area of China, whereas only 5.6% of the population lives in the west, taking up 64% of the land. What’s the reason for the uneven?
  • 3. 09/01/09
  • 4.
    • The population system keeps interacting with external factors, such as climate conditions and social disturbances, for which the relationships are difficult to calculate from numerical analyses.
  • 5.
    • Studies in historical geography have incorporated computer modeling and simulations into analytical techniques that attempt to explain how observed social phenomena may have emerged.
      • Kohler et al. (2000)
      • Dean (2000)
      • Christiansen and Altaweel (2006)
  • 6.
    • ABS-CA hybrid model
    • CA is used to simulate the geographic environment in raster format
    • ABS is used to simulate the population individuals who can perceive the environmental conditions and migrate autonomously in cellular space given the collected environmental information.
  • 7.
    • There are three different spatial scales involved in the model: agents, cells, and provinces
    09/01/09 Figure 1 The relationship between spatial scales
  • 8.
    • Agents represent population individuals who migrate and settle down in a cell.
    • Cells are the fundamental units that represent geographic space and settlement locations. A set of cells belonging to the same geographic region is defined as a province.
    • Provinces are used to store macro information about the cells within them, including the gross production of potential agriculture, the total area available for agriculture, and the population.
  • 9.
    • The geographic background of the model consists of 227×297 raster cells based on a land-cover layer of China, and a layer of rivers is also included to construct the environmental infrastructure
    • Each raster cell is defined as a residential unit (RU) in which the population can reside, except for the cells occupied by rivers.
  • 10.
    • Null : The cells that do not satisfy residential demands are in the “Null” state
    • Potential : Those with favorable environmental conditions but without any population yet are in the “Potential” state , and can be occupied by population individuals.
    • Existent : If one or more individuals live in a cell, it is in the “Existent” state.
  • 11.
    • Null: Each cell is in the null state when initialized.
    • From Null to Potential: If there is more than one river cell in the Moore neighborhood with radius 1, then the central cell changes to the Potential state.
    • From Potential to Existent: When any population settles in a Potential RU, the potential RU updates its state to Existent.
  • 12.
    • the agent-based model is composed of a population system and three assistant sub-systems: social, climate, and agricultural sub-system.
    09/01/09 Figure 2 The composition of agent-based model
  • 13.
    • Changes in the regional agricultural productivity supply motivate people to move between provinces for better living conditions
    • With the change of annual rain fall and average temperature , we calculate the agricultural productivity for each year by the following equation:
  • 14.
    • Four of the most famous and largest migration waves are considered:
      • the migration after the YongJia turmoil from 307 A.D. to 312 A.D., called the “Yongjia Migration,”
      • the migration after the AnShi turmoil from 755 A.D. to 763 A.D., called the “AnShi Migration,”
      • the migration after the JingKang turmoil in 1127 A.D., called the “JingKang Migration.”
      • the migration in 1671 A.D. to 1776 A.D., named the “Huguang Migration.”
  • 15.
    • Summary of the migration waves
    09/01/09 *:Source from Ge, Cao, & Wu (1993); **: Source from ***: Source from Wu(2001); ****: Source from Chen( 2005)
  • 16.
    • Initialization : 60 million individuals are assigned to 31 provinces according to the real provincial population density in 2 A.D. from historical research by Ge (1986).
    • Growth :The total population grows at a constant rate of 0.15%
  • 17.
    • Interaction between provinces :
      • Attraction: The motivation for population migration is differences in living conditions, especially agricultural supply.
      • Repulsion: The populations of other provinces are taken as the factors that prevent population agents from moving into a province.
      • T ij , the spatial interaction between province j and province i , is written following Wilson (1967):
  • 18.
    • Moving:
      • If the target RU is in the Existent state, then the agent will move in;
      • If the target RU is in the Potential state, then the agent will move in and the cell switches to the Existent state; and
      • If the target RU is in the Null state, then the agent continues to move and chooses a new target in the immigratory province.
  • 19.
    • The correlation coefficient between the simulation population of each province and the real statistical record in 2003 is 0.97, which shows the significant correlation between the two datasets.
  • 20. 09/01/09 Figure 4 The simulation distribution of population in 713A.D. Figure5 The simulation distribution of population in 1820A.D.
  • 21.
    • The spatial difference in North-south population distribution is emerged in about 918A.D.
    • The Anshi migration made the most significant contribution to the north-south population pattern inversion.
  • 22.
    • The phenomenon of 94% of the population living in east with 6% in the west began in about 1246 A.D. After that time, the proportion in the east has remained at around 94% to 95%.
    • Driving force:
      • The discrepancy of agricultural potential productivity in east-west have determined the final population distribution;
      • The climate change from 1230 to 1260 A.D. made the most contribution to the East-west pattern formation, which result in a warm and humid climate in the east leading to high agricultural density and a centralized population, and a cold and dry climate in the west causing a low and widely dispersed human population.
  • 23.
    • From 2 A.D. to 500A.D., the population’s center of gravity moved sharply toward the southeast, indicating that the population in the southeast increased .
    • From 900 A.D. to 1300 A.D., the population’s center of gravity continued moving toward the south, with only small changes in longitude. This reflects the stability of the population distribution in the east-west direction during this period.
    • After 1300 A.D., the population’s center of gravity shifted in both longitude and latitude in small range. Population distribution runs to stable.
  • 24.
    • Agent-based simulations in historical geography can not only reproduce the dynamic evolution of a historical phenomenon, but can also be used to develop scenario tests for further analysis.
    • The north-south population distribution is shaped in about 918A.D. contributed by the Anshi migration most.
    • The east-west population distribution is shaped in about 1246A.D. promoted by the climate change in 1230-1260 most.
  • 25.
    • Thanks for your attention!