Five centuries of urban growth: Impacts on food security and soil functionality

• Santiago’s growth (1541–2017) reduced reduced soil productivity equivalent to feeding 2.5 million people annually. • Between 1930 and 2017, 94.5% of this productivity loss occurred. • The greatest losses were between 1985 and 2002. • By 2020, fruit orchards replaced grain cropland, reducing the potential to feed 1.6 million people annually. Urban expansion poses a global threat to soil and food security, particularly as cities often grow on highly fertile agricultural lands. This study examines the impacts of Santiago de Chile’s urban growth from its founding in 1541 to recent years, focusing on soil functionality and its implications for food security. We estimate the biocapacity of soils by disaggregating the Yield Factor from district to soil series level, applying crop mapping based on their phenology and texture image analysis. We then analyze the impacts of urban expansion on soil security by reconstructing soils impacted by urbanization at various periods. Field results indicate correct mapping accuracy of 69% and 81% for wheat and maize, respectively. The urban historical expansion of Santiago primarily covered highly productive soils, with 92% of the soil series exceeding the world average soil productivity, and 64% being at least twice as productive. Urbanization has reduced the potential to feed 2.5 million people per year. In comparison, the recent expansion of fruit orchards on the remaining agricultural grain crop land could have fed an additional 1.6 million people if used for staple crops. These findings highlight the effect of applying severe trade-offs in land use decisions, with 94.5% of the loss of soil productivity occurring between 1930 and 2017. Recent periods implied the greatest loss considering annual rates, with 1985-2002 being almost three times greater than 1930-1985 and 2002-2007 being 2.5 times greater. These findings underscore the urgent need for soil security perspectives in urban planning to safeguard both local and global food systems.