Cause & Effect

The difference in
temperature between rural and urban areas,
depends on various factors:

  • Presence of circulating fresh air corridors.
  • Energy balance of materials used in built-up areas.
  • Limited evapotranspiration due to the reduction of permeable surfaces.
  • Albedo drop in urban environment (Susca et al. 2011).

POPULATION growth

According to a projection drawn up by the United Nations (UN, 2004), the world population will reach its peak in 2075, with over 9 billion inhabitants.
In line with this Trend, an increasing number of people are moving to large cities (54% according to the Department of Economic and Social Affairs, in 2014).
The highest levels of urbanisation (more than 70% of the total) have been reached and are continuing to grow predominantly in Europe, North America, Latin America and Oceania. The phenomenon is still contained in Africa and Asia but the figure is rapidly rising.
The percentage of people living in cities will increase to 66% by 2050.
By 2030, the rate of urbanised land is expected to triple with respect to the area surveyed in 2000, increasing by 1.2 million square kilometres (Seto et al. 2012).

URBANISATION AND ENERGY CONSUMPTION

In addition to urban areas and the population, energy consumption is also growing strongly. Cities currently consume 80% of the energy produced.
The effects of Global Warming and
growth in economic development will lead to a rise in demand for cooling systems.

Artificially cooled areas grew 12-fold between 2000 and 2020 and the demand for air-conditioned cooling is expected to rise 40-fold by 2100 (Lucas & Parisi 2013).

HUMAN IMPACT ON LAND

Human beings have been altering the Earth’s surface since time immemorial. Artificial changes in land use (tree felling, seed planting, mining and the construction of cities) have profoundly changed and deteriorated the Earth’s surface.
This specific period of time marked by human activity, has been called the “Anthropocene”.
Today, more than 50% of the Earth’s surface has been altered by humankind (Pedraza et al. 2012); between 1945 and 1995, for example, 17% of the primordial vegetated soil was degraded by deforestation and industrial activity (Daily 1995).
Research studies by Pedraza, Hooke & Martin-Duque (2012) show that by 2050, the world population will cover almost 50% of our planet’s available land.
Projections show that the percentage of land covered by the expansion of cities, among other activities, is significantly increasing.
Land degradation by humans is mainly due to population growth, urbanisation, economic interests and the production of food.

SOIL SEALING

Today, the ratio of sealed (impermeable) soil per inhabitant is 200 mq (IASS 2013).
It is predicted that the cemented and impermeable surface area in cities will triple by 2030 in developed countries (IASS 2013).

In addition to the increase in demand for living space due to population growth, the demand for space per capita is also on the rise.
These two trends will cause an increase in the number, size and density of cities in developed countries.

ALTERATION OF WATER CYCLE AND URBAN STORMWATER

The strong change in land use significantly affects available water sources.
Moreover, carbon dioxide (CO2), previously trapped in soil and plants, is released into the atmosphere, contributing to global climate change and warming. Soil sealing causes a noticeable localised increase in heat.
This phenomenon leads to a significant decrease in combined plant-soil evapotranspiration effect and consequent decrease in rainfall (Wei et. al. 2009). This chain of events results in heavy rainfall, floods and periods of drought (Pedraza eta al. 2012, Wei et al. 2009).
Studies (Kravcik et al. 2008) show that 50-65% of the earth’s water “returns” in the form of repeated precipitation in the same area (City).
Any variation/change in land use will inevitably alter the Water-Energy exchange cycle within the entire Earth’s atmosphere.
Changes in the global and local water cycle affect the world’s climate (Wei et al. 2009). Soil alterations primarily affect the local water cycle.