Cheryl Gann
NCSSM Instructor of Mathematics
gann@ncssm.edu
Special Thanks to Linda Schmalbeck, NCSSM Instructor of Biology, for
the activity inspiration.
Six Major Reservoirs
Water Cycle Processes
Residence Time Comparison
Reservoir
Residence Time
Glaciers
20 to 100 years
Seasonal Snow
Cover
2 to 6 months
Soil Moisture
1 to 2 months
Lakes
50 to 100 years
Rivers
2 to 6 months
Groundwater:
Shallow
100 to 200 years
Groundwater:
Deep
10,000 years
Reservoir
Residence Time
Snow & Ice*
27,500 years
Surface Water
2.55 years
Groundwater
4,100 years
Table on Left: Pidwirny, M. (2006). "The Hydrologic Cycle". Fundamentals of Physical Geography, 2nd Edition.
Date Viewed 1/20/2013. http://www.physicalgeography.net/fundamentals/8b.html.
*Some of the ice in the ice sheet that covers most of the continent of Antarctica has been there for nearly a
million years: http://www.windows2universe.org/earth/polar/cryosphere_intro.html
Residence Time Comparison
Reservoir
Residence Time
Reservoir
Residence Time
Oceans
3,000 years
Oceans
3,103 years
Marine
Atmosphere
9.23 days
Land
Atmosphere
15.21 days
Atmosphere
8 days
“A drop of water may spend over 3,000 years in the ocean before moving on to another part of the water cycle
while a drop of water spends an average of just eight days in the atmosphere before falling back to Earth.”
http://www.windows2universe.org/earth/polar/cryosphere_intro.html
Glacier Melting
 Global sea level is currently rising as a result of both ocean thermal
expansion and glacier melt, with each accounting for about half of
the observed sea level rise, and each caused by recent increases in
global mean temperature.
 For the 21st century, the IPCC projected that melting of glaciers and
ice caps will contribute roughly 10-12 cm to sea level rise, with an
uncertainty of roughly a third. This would represent a melting of
roughly a quarter of the total amount of ice tied up in mountain
glaciers and small ice caps.
 The IPCC notes that as much as 33% of coastal land and wetland
habitats are likely to be lost in the next hundred years if the level of
the ocean continues to rise at its present rate.
National Snow & Ice Data Center. State of the Cryosphere. http://nsidc.org/cryosphere/sotc/glacier_balance.html.
Intergovernmental Panel on Climate Change (IPCC). 2007. IPCC Fourth Assessment Report - Climate Change 2007:
The Physical Science Basis Summary for Policymakers.
Sea Rise Calculations
360 𝑘𝑚3 of water will raise the oceans approximately 0.1 𝑐𝑚
1000 𝑘𝑔 of water = 10−9 𝑘𝑚3
360
𝑘𝑚3
1000 𝑘𝑔
12 𝑘𝑔 = 0.36 ⋅ 1015 𝑘𝑔
⋅ −9
=
360
⋅
10
10 𝑘𝑚3
0.36 ⋅ 1015 𝑘𝑔 of water will raise the oceans approximately 0.1 𝑐𝑚
Overdrafting
Overdrafting is the process of extracting groundwater beyond
the equilibrium yield of the aquifer.
 Overdrafting increases the total amount of water within the
hydrosphere.
 Since more water is subject to transpiration and evaporation, there is
accretion in water vapor and cloud cover which are the primary
absorbers of infrared radiation in the Earth's atmosphere.
 Large-scale groundwater extraction for irrigation, drinking water or
industry results in an annual rise in sea levels of approximately 0.8 mm,
accounting for about one-quarter of total annual sea-level rise (3.1 mm).
 According to hydrologists from Utrecht University and the research
institute Deltares, the rise in sea levels can be attributed to the fact that
most of the groundwater extracted ultimately winds up in the sea.
http://www.uu.nl/EN/Current/Pages/Wereldwijdonttrekkenvangrondwaterleidttotzeespiegelstijging.aspx
Saltwater Intrusion
Sea water moving inland is called a saltwater intrusion.
 Groundwater extraction is the primary cause of saltwater intrusion.
 Groundwater extraction can lower the level of the freshwater table,
reducing the pressure exerted by the freshwater column and
allowing the denser saltwater to move inland.
Barlow, Paul M. (2003). "Ground Water in Freshwater-Saltwater Environments of the Atlantic Coast". USGS.
“Our 50-year observed global surface salinity changes,
combined with changes from global climate models,
present robust evidence of an intensified global water
cycle at a rate of 8 ± 5% per degree of surface warming.
This rate is double the response projected by currentgeneration climate models and suggests that a
substantial (16 to 24%) intensification of the global water
cycle will occur in a future 2° to 3° warmer world.”
"Ocean Salinities Reveal Strong Global Water Cycle Intensification During 1950 to 2000”.
Science 336 (6080): 455-458. 27 April 2012.