water resources assessment

World of Salt: Total Global Saltwater and Freshwater Estimates
Estimates of global water resources based on several different calculation methods have produced varied estimates. This graphic illustrates the proportions of saltwater and freshwater that make up the earth's water resources, and explains where these resources are located.

2. Global Freshwater Resources: Quantity and Distribution by Region
Glaciers and icecaps contain approximately 70% of the world's freshwater, but groundwater is by far the most abundant and readily available source of freshwater. This graphic illustrates the quantity and distribution of the world's freshwater resources in glaciers and icecaps, groundwater, and in wetlands, large lakes, reservoirs and rivers.
3. Major River Basins of the World
Rivers form a hydrological mosaic, with an estimated 263 international river basins covering 45.3% of the land surface area of the earth, excluding Antarctica. This graphic shows the locations of 26 of the world's major river basins.
4. Major River Basins of Africa
This graphic shows the locations of 13 major river basins in Africa.
5. The World's Water Cycle and Estimated Residence Times of the World's Water Resources
The water cycle consists of precipitation, evaporation, evapotranspiration and runoff. This graphic explains the global water cycle, showing how nearly 577 000 km3 of water circulates through the cycle each year. A table of estimated residence times of the world's water shows the estimated times that water resources exist as biospheric water, atmospheric water and so on.
6. The World's Surface Water: Precipitation, Evaporation and Runoff by Region
The world's surface water is affected by different levels of precipitation, evaporation and runoff in different regions. This graphic illustrates the different rates at which these processes affect the major regions of the world, and the resulting uneven distribution of freshwater.

7a. River Runoff through the 20th Century
River runoff is cyclical in nature, with alternating cycles of wet and dry years. These graphics show the average annual volumes of river runoff by continent and the deviations from average amounts of runoff for most of the 20th century.
7b. River Runoff through the 20th Century
7c. Variations in River Runoff by Continent through most of the 20th Century
8. Global Sediment Loads: Suspended Sediment Discharged by Region
Asia exhibits the largest runoff volumes and, therefore, the highest levels of sediment discharge. This graphic shows the amounts of suspended sediments discharged every year in the major regions of the world.

9. Biological Oxygen Demand (BOD), 1976-2000 and Freshwater Alkalinity, 1976-2000
Biological oxygen demand is an indicator of the organic pollution of freshwater. Alkalinity is another indicator of freshwater quality. These graphics compare the concentrations of these two factors in the major regions of the world for the periods 1976 to 1990 and 1991 to 2000.
10. Global Average Nitrate Levels and Global Dissolved Phosphate Levels
Average concentrations of nitrate at major river mouths have not changed significantly between 1976 to 1990 and 1991 to 2000. There have been some changes, however, in phosphate concentrations at major river mouths. These graphics compare nitrate levels and phosphate levels for 1976-1990 and 1991-2000, and illustrate the changes that have occurred between the two time periods.
11. Global International Waters Assessment (GIWA) Case Studies.
The Global International Waters Assessment (GIWA) is an example of a comprehensive strategic assessment designed to identify priorities for remedial and mitigatory actions in international waters. This graphic shows GIWA case studies for the Black Sea, the Amazon, the Great Barrier Reef and the Agulhas Current.

12. Global International Water Assessment Tools for Better Monitoring of the World's Water Resources
GIWA's assessment tools for monitoring the world's water resources, incorporating five major environmental concerns and application of the DPSIR framework, are now beginning to yield results of practical use for management decisions. This graphic explains the GIWA Assessment Methodology and GIWA's main environmental concerns.
13. The DPSIR Framework (Driving Forces- Pressures- Impacts- State- Responses)
The DPSIR framework is used to assess and manage environmental problems. This graphic explains the DPSIR process.
Global Water Withdrawal and Consumption
Freshwater use is partly based on several socio-economic development factors, including population, physiography, and climatic characteristics. This graphic illustrates freshwater use from 1900 to 2000 for the world's major regions, and projects freshwater use for 2000 to 2025.

15. Evolution of Global Water Use and Industrial and Domestic Consumption Compared with Evaporation from Reservoirs.
Throughout the 20th century, global water use has increased in the agricultural domestic and industrial sectors. Evaporation from reservoirs has increased at a slower rate. Projections indicate that both global water use and evaporation will continue to increase.
16. Freshwater Withdrawal by Sector in 2000
The agricultural sector is by far the biggest user of freshwater. This graphic shows the relative percentages of water use by the agricultural, industrial and domestic sectors in 2000.
17. Global Freshwater Withdrawal: Country Profiles Based on Agricultural, Industrial and Domestic Use
This graphic makes it possible to compare water use by the agricultural, industrial and domestic sectors at the national level.
18. Water Supply and Sanitation Coverage
The supply of safe drinking water and the provision of sanitation are management issues that raise concerns of inequitable service provision, particularly in developing countries. This graphic shows water supply and sanitation coverage in urban and rural areas, and compares global water supply and sanitation coverage with that of developing countries.