Surface Water




Current distribution of global surface water resources
The map was created by analysing more than three million satellite scenes from the USGS/NASA Landsat satellite programme archive (1984 through 2015). This is more than 1 823 Terabytes of data (equivalent to 546 million MP3 songs). From these data, global maps of surface water occurrence and change with a 30 m resolution were created by the EC-JRC.
Source: WAD3-JRC, 2018, based on Pekel, J.-F.


Global distribution varies dramatically in space and time

At the global scale, surface water is a dynamic resource1. While surface water is only one part of the global water resource, it is the most readily accessible for human use and provides wide-ranging ecosystem services. Over the past three decades, 3 % of the Earth’s landmass (4 476 571 km2) has been covered by water for at least some period of time. Permanent lakes and rivers comprise about 60 % of surface water, while the rest occurs as episodic events, including seasonal (e.g. monsoons) and sporadic (e.g. once every few years) events. Most surface water is freshwater, but there is no accurate data available on the proportions of fresh/brackish/saline waters.
When and where surface water occurs on the planet is critically important. Water availability is relevant to almost all socio-economic and environmental impacts of climate and demographic changes and has far-reaching implications for sustainability. The presence or absence of surface water on the planet’s landmass influences the physical climate system because it affects the exchange of heat, gas and water vapor between the planet’s surface and atmosphere. Surface water sustains ecological systems on which terrestrial life depends. It affects our capacity to grow crops and raise animals, underpins industrial processes, influences the movement of diseases and toxins, generates energy, can cause loss of life and damage to property and infrastructure and also has immense spiritual, recreational and cultural value in our lives. Surface water is therefore a fundamental land resource.
North America accounts for 52 % of the planet’s truly permanent water resources and 15 % of contemporary seasonal water, but has just 5 % of the human population. In contrast Asia, with 60 % of the human population, has only 9 % of the truly permanent and 35 % of the contemporary seasonal water. Africa and Latin America have almost the same share of the world’s permanent water at around 9 % each, though their populations are very different, with Africa (16 % of the total) supporting nearly twice as many people as Latin America (8.6 %). Europe, including Russia, with 10 % of the global population has 22 % of the permanent water and 18 % of the contemporary seasonal water.

Shares of global water surface area, human population and area equipped for irrigation by continent.
Source: WAD3-JRC: water surface; human population; irrigation.

Shares of global water surface area, human population and area equipped for irrigation by continent.
Source: WAD3-JRC: water surface; human population; irrigation.

Shares of global water surface area, human population and area equipped for irrigation by continent.
Source: WAD3-JRC: water surface; human population; irrigation.

Relative and absolute proportion of water transition classes for non-dryland and dryland areas.
Source: WAD3-JRC, 2018, based on Pekel, J.-F.

Since 1900, there has been a dramatic increase in the amount of land put under irrigation globally. The increase is particularly pronounced in south and east Asia. (AEI=area equipped for irrigation; HID=historical irrigation data set).
Source: Siebert et al., 2015.

The mass of water on Earth remains fairly constant over time, but its partitioning into the major reservoirs of ice, fresh water, saline water and atmospheric water varies depending on a wide range of climatic variables. The water moves from one reservoir to another, such as from river to ocean, or from the ocean to the atmosphere, by the physical processes of evaporation, condensation, precipitation, infiltration, surface runoff and subsurface flow.
Source: WAD3-JRC, 2018.