Category: Freshwater Planetary Boundary

Blue, green, gray water flows and pools; river basins and modifications; groundwater; water sanitation

Water Supply and Sanitation

Binh thanh district, Ho Chi Minh, Vietnam  Photo by Anh Vy on Unsplash
  • The percentage of global population using at least a basic drinking water service rose from 81 to 89% between 2000 and 2015
  • 3 out of 10 (2.1 billion; 29% global population) did not have a safely managed drinking water service in 2015
  • 844 million still lacked even a basic drinking water service
  • Water-related deaths impact thousands and costs billions

Average annual impact from inadequate drinking water and sanitation services, water-related disasters. Adapted from WWAP (UNESCO World Water Assessment Programme). 2019. The United NationsWorld Water Development Report 2019: Leaving No One Behind. Paris, UNESCO

In 2015, an estimated 2.1 billion people lacked access to safely managed drinking water services and 4.5 billion lacked access to safely managed sanitation services. (WWAP)

Almost half of people drinking water from unprotected sources live in Sub-Saharan Africa, where the burden of collecting water lies mainly on women and girls, many of whom spend more than 30 minutes on each trip to collect water. (WWAP)

Proportion of population using at least basic drinking water services, 2015
Source: WWAP (UNESCO World Water Assessment Programme). 2019. The United NationsWorld Water Development Report 2019: Leaving No One Behind. Paris, UNESCO


  • Worldwide, only 2.9 billion people (39% of global population) used safely managed sanitation services in 2015.  40% of these people lived in rural areas.
  • 2.1 billion people had access to “basic” sanitation services.
  • 2.3 billion (one out of every three people) lacked even a basic sanitation service—nearly 1 billion people (892 million) still practiced open defecation.
Photo: SuSanA Secretariat. Creative Commons BY (cropped)

Global and regional sanitation coverage, 2015.  Source:  The United Nations World Water Development Report 2019: Leaving No One Behind. Paris, UNESCO, 2019.


World’s largest distributed store of freshwater


  • Total groundwater volume in the upper 2 km of continental crust is approximately 22.6 million km3 of which 0.1-5.0 million km3 is less than 50 years old1
  • The volume of modern groundwater is equivalent to a body of water with a depth of about 3 meters spread over the continents2
  • Groundwater replenished over a human lifetime of 25-100 years is a finite, limited resource with a spatially heterogeneous distribution dependent on geographic, geologic and hydrologic conditions3
  • Accounts for as much as 33% of total global water withdrawals4
  • Over 2 billion people rely on groundwater as their primary water source5
  • 50% or more of the irrigation water used to grow the world’s food is supplied by groundwater6

            Source:  1,2,3–Gleeson, T., Befus, K. M., Jasechko, S., Luijendijk, E., & Cardenas, M. B.   (2015). The global volume and distribution of modern groundwater. Nature           Geoscience, 9(2), 161–167.doi:10.1038/ngeo2590 

            4,5,6–Famiglietti, J. S. (2014). The global groundwater crisis. Nature Climate Change,   4(11), 945–948.doi:10.1038/nclimate2425 

Groundwater Use by Country, in cubic kilometers per year

Source:  Fienen M.N., Arshad M. (2016) The International Scale of the Groundwater Issue. In: Jakeman A.J., Barreteau O., Hunt R.J., Rinaudo JD., Ross A. (eds) Integrated Groundwater Management. Springer, Cham, DOI The International Scale of the Groundwater Issue

37 Largest Aquifer Systems

Source: Map and table):  Richey, A. S., B. F. Thomas, M.-H. Lo, J. T. Reager, J. S. Famiglietti, K. Voss, S. Swenson, and M. Rodell (2015), Quantifying renewable groundwater stress with GRACE, Water Resour. Res.,51, 5217–5238, doi:10.1002/2015WR017349
Aquifer Map # Aquifer Name
1 Nubian Aquifer System (NAS)
2 Northwestern Sahara Aquifer System (NWSAS)
3 Murzuk-Djado Basin
4 Taoudeni-Tanezrouft Basin
5 Senegalo-Mauritanian Basin
6 Iullemeden-Irhazer Aquifer System
7 Lake Chad Basin
8 Sudd Basin (Umm Ruwaba Aquifer)
9 Ogaden-Juba Basin
10 Congo Basin
11 Upper Kalahari-Cuvelai-Upper Zambezi Basin
12 Lower Kalahari-Stampriet Basin
13 Karoo Basin
14 Northern Great Plains Aquifer
15 Cambro-Ordovician Aquifer System
16 Californian Central Valley Aquifer System
17 Ogallala Aquifer (High Plains)
18 Atlantic and Gulf Coastal Plains Aquifer
19 Amazon Basin
20 Maranhao Basin
21 Guarani Aquifer System
22 Arabian Aquifer System
23 Indus Basin
24 Ganges-Brahmaputra Basin
25 West Siberian Basin
26 Tunguss Basin
27 Angara-Lena Basin
28 Yakut Basin
29 North China Aquifer System
30 Song-Liao Basin
31 Tarim Basin
32 Paris Basin
33 Russian Platform Basins
34 North Caucasus Basin
35 Pechora Basin
36 Great Artesian Basin
37 Canning Basin

Global Aquifer Depletion Hotspots in Arid and Semi-arid Zones

Aquifer Country
Northwest Sahara      #2 Algeria, Libya, Tunisia

California Central Valley 
High Plains (Ogallala) #17 USA
Guarani                    #21 Argentina, Brazil, Paraguay, Uruguay
Northern Middle East Iran, Iraq, Syria, Turkey
Arabian                      #22 Iraq, Jordan,Oman,Qatar,Saudi Arabia,
UAE, Yemen
Northwestern India #23 India, Pakistan
North China Plain      #29 China
Canning Basin         #37 Australia

Adapted from:  Famiglietti, J. S. (2014). The global groundwater crisis. Nature Climate Change, 4(11), 945–948.doi:10.1038/nclimate2425 

Highlights from Global Aquifer Hotspots: Central Valley, California (#16)

  • Most productive agricultural area in the United States
  • 40%+ of Central Valley’s water supply comes from gw, primarily to meet agricultural demand
  • Groundwater use increased from 0.75 to 2.5 km3 per year between 1962-2003
  • 2007-2010 severe drought caused a permanent aquifer system storage loss of ~2%, due to irreversible compaction of the aquifer system
    • Source: Ojha, et al., Sustained Groundwater Loss in California’s Central Valley Exacerbated by Intense Drought Periods, Water Resources Research, June 2018, 54(5575). Doi:  10.1029/2017WR022250)Most productive agricultural area in the United States

May 7, 2015 – September 10, 2016
Several trouble spots that were identified in 2015 have continued to subside at rates as high as 0.6 meters (2 feet) per year. Significant subsidence was measured in subsidence bowls near the towns of Chowchilla, south of Merced; and Corcoran, north of Bakersfield. These bowls cover hundreds of square kilometers and continued to grow wider and deeper between May 2015 and September 2016. Subsidence also intensified near Tranquility in Fresno County, where the land surface has settled up to 51 centimeters (20 inches) in an area that extends 11 kilometers (7 miles).  NASA Earth Observatory map by Joshua Stevens, using modified Copernicus Sentinel SAR data (2016) courtesy of Tom Farr and Cathleen Jones, NASA Jet Propulsion Laboratory. Caption by Alan Buis (Jet Propulsion Laboratory) and Ted Thomas, California Department of Water Resources; edited by Mike Carlowicz.

Declining groundwater storage appears to be part of the Central Valley’s future

Central Valley groundwater storage trends and simulations
The GWD Model simulations for both the past and future years. The simulated groundwater storage changes for the years 1980–2014 (Blue line) are compared with observations (red icons). In future years, several precipitation scenarios are examined.
Source:  Massoud, E., et al., Projecting groundwater storage changes in California’s Central Valley, Scientific Reports 8(1), August 2018. Doi:10.1038/s41598-018-31201-1
Highlights from Global Aquifer Hotspots: High Plains Aquifer (United States) #17 (The International Scale of the Groundwater Issue)
  • One of the largest gw aquifers in the world (8 states; 450,000 km2)
  • Provides drinking water for 2.3 million people
  • Extensively used for agricultural production
  • Storage decline from 1950-2007 accounts for 36% of total gw depletion during 1900-2008
  • Depletion is highly variable spatially; very high depletion rates in the southern and central HP, large areas of Texas and Kansas. Low/no depletion in the northern HP aquifer (#14)

November 1, 1998-October 331, 2016
The High Plains Aquifer, also known as the Ogallala Aquifer, is under stress. Farmers today have to drill ever deeper wells in order to pump water for irrigation, and one recent study found the aquifer to be under more strain than any other in the United States. About 30 percent of the water once stored beneath Kansas is already gone, and another 40 percent will be gone within 50 years if current trends continue.  The map at the left of this page shows irrigation frequency in the basin between 1999 and 2016. Areas watered nearly every year are purple; those watered only rarely are yellow. The extent of the Ogallala Aquifer is shown with gray. The second image highlights the variability in irrigation between center-pivot irrigation fields in an area along the Colorado-Nebraska border. The most widely grown crops in the basin are corn and wheat.  NASA Earth Observatory maps by Lauren Dauphin, using data from Deines, Jillian, et al. (2017). Story by Adam Voiland.
Highlights from Global Aquifer Hotspots: Northwest India (#23) The International Scale of the Groundwater Issue
  • India is the world’s largest consumer of gw
  • 1/3 of India’s aquifers are overexploited, semicritical, or critical
  • 70% of India’s agricultural production depends on gw
  • GW is the primary source (85%) of drinking water for rural areas
  • GW is typically extracted by tubewells (~15 million)
  • In Northwestern India (Rajasthan, Punjab, Haryana, including Delhi) gw has been unsustainably depleted between 2000-2008 in an amount equivalent to double the capacity of India’s largest surface-water reservoir (Rodell, et al., 2009)
  • This region has a population of approximately 114,000,000.
Highlights from Global Aquifer Hotspots: North China Plain (#29) The International Scale of the Groundwater Issue
  • Region supplies nearly half of China’s wheat and one-third of other cereal grains
  • Population is more than 200,000,000
  • Rapid groundwater depletion since the 1980’s
  • Saltwater intrusion into the freshwater aquifer due to groundwater depletion has salinized 44% of the total area between the coastal plain and Laizhou city.

Endorheic Basins

What remains of the large inland lake is a fraction of what it was in the 1950s and 60s. In those years, the government of the former Soviet Union diverted so much water from the Amu Darya and Syr Darya—the regions’ two major rivers—to irrigate farmland, that it pushed the hydrologic system beyond the point of sustainability. During subsequent decades, the fourth largest lake in the world shrank to roughly a tenth of its former size and divided into several smaller bodies of water.

Source: Endorheic global decline

Definition:  surface flow is landlocked from the ocean


  • Cover 20% of the Earth’s land surface, and nearly 50% of its water-stressed regions
  • Decreases appear to be related to recent climate conditions in conjunction with direct human activities

Terrestrial Water Storage Changes in Endorheic Basins April 2002-March 2016

Adapated from Table 1 Endorheic global decline
*Terrestrial Water Storage = Groundwater + soil moisture + surface waters + snow + ice

River Basin Modifications

Aswan High Dam, April 12, 2015  NASA Earth Observatory.  Astronaut photograph ISS043-E-101953 was acquired on April 12, 2015

Environmental Significance

Source:  Grill, et al., Mapping the world’s free-flowing rivers, Nature 569(7755):215-     221, doi: 10.1038/s41586-019-1111-9

  • Destruction/separation of floodplains from rivers alters ecosystem services such as natural flood storage, nutrient retention and flood-recession agriculture
  • Built river infrastructure has been linked to declines in terrestrial and freshwater species
  • Sediment capture by dams may cause alteration of the geomorphic dynamics of rivers and the shrinking of river deltas worldwide
  • Inland fisheries provide the equivalent of all dietary animal protein for 158 million people worldwide
  • Only 37% of rivers longer than 1,000 kilometers remain free-flowing in their entire length
  • Only 23% of rivers longer than 1,000 kilometers flow uninterrupted to the ocean
  • Very long free-flowing rivers are largely restricted to remote regions of the Arctic and of the Amazon and Congo basins
  • In densely populated areas, only a few very long rivers remain free-flowing, such as the Irawaddy and Saleen

Dams and Reservoirs

  • the leading contributors to the loss of river connectivity
  • There are approximately 2.8 million dams (with reservoir areas >1000 cubic meters) regulating and creating over 500,000 kilometers of rivers and canals for navigation and transport and building irrigation and water-diversion schemes
  • More than 3,700 hydropower dams (>1MW) are currently planned or under construction worldwide.
2019 Hydropower Status Report
More than 21.8 Gw of hydroelectric capacity was put into operation in 2018
2019 Hydropower Status Report
Electricity generation from hydropower projects achieved a record 4,200 terawatt hours (TWh) in 2018, the highest ever contribution from a renewable energy source, as worldwide installed hydropower capacity climbed to 1,292 GW, according to the 2019 Hydropower Status Report
China added the most capacity with the installation of 8,540 megawatts, followed by Brazil (3,866 MW), Pakistan (2,487 MW), Turkey (1,085 MW), Angola (668 MW), Tajikistan (605 MW), Ecuador (556 MW), India (535 MW), Norway (419 MW) and Canada (401 MW).
Brazil has now overtaken the United States as the second largest producer of hydroelectricity by installed capacity, after 3,055 MW was put into operation last year at the 11,000 MW Belo Monte complex in the country’s northeast.

Small Hydropower Plants (SHP)

Source:  Couto, T. B., & Olden, J. D. (2018). Global proliferation of small hydropower plants – science and policy. Frontiers in Ecology and the Environment, 16(2), 91–100.doi:10.1002/fee.1746 

Definition:  Considerable variability in definition across countries; refers broadly to facilities that produce less electricity and operate in smaller rivers as compared to large hydropower plants.  Vary greatly in level of flow control, storage capacity, diversion structures.  70% of countries classify as installations with less than 10 MW capacity


  • There are close to 11 SHPs for every large hydropower plants (LHPs) = 11% of global hydropower electricity generation
  • 82,891 SHPs are operating or under construction in 150 countries
  • 181,976 new plants may be installed if all potential capacity were developed
  • 10,569 new projects appear in national plans
  • China has the world’s largest number of SHPs—47,073; 57% of the world’s SHPs
  • Europe has 26,877 SHPs
  • Future plans for SHPs are concentrated in Asia, the Americas, Southern and Eastern Europe and East Africa

            Environmental Impacts

  • Similar to LHPs; but SHPs generally occur in smaller rivers, which is significant given the ecological importance of headwater streams
  • Cumulative ecological impacts of SHPs (multiple installations in the same river basin) appears to be an underappreciated issue

Freshwater Planetary Boundary

Freshwater consumption and the global hydrological cycle

“The freshwater cycle is strongly affected by climate change and its boundary is closely linked to the climate boundary, yet human pressure is now the dominant driving force determining the functioning and distribution of global freshwater systems. The consequences of human modification of water bodies include both global-scale river flow changes and shifts in vapour flows arising from land use change. These shifts in the hydrological system can be abrupt and irreversible. Water is becoming increasingly scarce – by 2050 about half a billion people are likely to be subject to water-stress, increasing the pressure to intervene in water systems.  A water boundary related to consumptive freshwater use and environmental flow requirements has been proposed to maintain the overall resilience of the Earth system and to avoid the risk of ‘cascading’ local and regional thresholds.”
Stockholm Resilience Planetary Boundaries


  • Two control variables:
    • Global–Maximum amount of consumptive blue water use
      • 4000 cubic km/year (4000-6000 km3/yr)
    • Regional (River Basin)–Blue water withdrawal as % of mean monthly river flow
  • Current Global value (river basin not determined): 2600 km3/year

Hydrological Cycle in the Anthropocene

Source:  (Global Hydrological Cycle in the Anthropocene) This commonly reproduced image from the USGS of the averaged depiction of the hydrological cycle does not represent important seasonal and interannual variation in many pools and fluxes.
A hydrologic cycle in the Anthropocene should include:

  • Include anthropogenic influences
  • Include global teleconnections
  • Multiple catchments
  • Endorheic basins
  • Estimates of green, blue, and grey water use

Estimates of Global Pools and Fluxes of Water

Estimates of pools and fluxes are based on a synthesis of approximately 80 recent and global-scale studies; volumes represent the central point of the most recent or comprehensive individual estimates. Adapted from Abbott, et al., Nature Geoscience 12, 533–540. 2019
  • Based on the figures in the previous table, human appropriation (~24,000 km3yr-1) redistributes the equivalent of half of global river discharge or double global groundwater recharge
  • Irrigated agriculture is the largest water consumer, accounting for ~85-90% of water consumption, followed by industrial, and domestic water use
  • Global water consumption rose 40% between 1980 (~1,200km3) and 2016 (~1,700km3).

Global and Sectoral Water Consumption 2016

Adapted from: Qin, et al., Flexibility and intensity of global water use,Nature Sustainability 2, 515-523 (2019)

Top Six Water Stressed River Basins by Continent 2012-2016 5-year Index

In each continent, the basin is selected as the one having the largest water stress index among the top 10% basins that have substantial electricity generation, crops production, human population, livestock and dam capacity in each continent.

Source:  Source:  Qin, et al., Flexibility and intensity of global water use, Nature Sustainability 2, 515-523 (2109)

Global Demands on Freshwater

Source:  Wu, N., Wang, C., Ausseil, A. G., Alhafedh, Y., Broadhurst, L., Lin, H. J., Axmacher,J., Okubo, S., Turney, C., Onuma, A., Chaturvedi, R. K., Kohli, P., Kumarapuram Apadodharan, S., Abhilash, P. C., Settele, J., Claudet, J., Yumoto, T., Zhang, Y. Chapter 4: Direct and indirect drivers of change in biodiversity and nature’s contributions to people. In IPBES (2018): The IPBES regional assessment report on biodiversity and ecosystem services for Asia and the Paci c. Karki, M., Senaratna Sellamuttu, S., Okayasu, S., Suzuki, W. (eds.). Secretariat of the Intergovernmental Science-Policy Platform on Biodiversity and Ecosystem Services, Bonn, Germany, pp. 265-370.

Over 2 billion people live in countries experiencing high water stress. Recent estimates show that 31 countries experience water stress between 25% (which is defined as the minimum threshold of water stress) and 70%. Another 22 countries are above 70% and are therefore under serious water stress.

It has been estimated that about 4 billion people, representing nearly two-thirds of the world population, experience severe water scarcity during at least one month during the year.

Global overview of countries experiencing different levels of water stress
(the ratio of total freshwater withdrawn annually by all major sectors, including environmental water requirements, to the total amount of renewable freshwater resources, expressed as a percentage). Source: WWAP (UNESCO World Water Assessment Programme). 2019. The United NationsWorld Water Development Report 2019: Leaving No One Behind. Paris, UNESCO

Trends in Terrestrial Water Storage (TWS) April 2002-March 2016

Adapted from Rodell, et al. 2018; based on Figure 1 and Table 1
Terrestrial Water Storage = Groundwater + soil moisture + surface waters + snow + ice