Category: Global Pools and Fluxes

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

Status:

  • 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 https://science.sciencemag.org/content/347/6223/1259855

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) https://doi.org/10.1038/s41893-019-0294-2

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) https://doi.org/10.1038/s41893-019-0294-2

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‚Äôs 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