Global Change and The Hydrological Cycle

1
Global Change and The Hydrological Cycle

• GE1
• Human-Environment Interactions
• MT 2008

2
Contents

• Part 1 Anthropogenic changes to terrestrial
  hydro-cycle
• Part 2 Climate change and the hydro-cycle
• Part 3 Water scarcity, demand and climate change

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Growth in Water Use
Source Gleick et al., 2001
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Irrigated Agriculture

• 1.09-fold increase in cultivated area
• 6.87-fold increase in N-fertiliser input
• 3.48-fold increase in P-fertiliser input

Source Tilman 1999
5
Other contributing factors

• Industrialisation energy production
• Rural to urban shift
• Increased wealth

6
Increased Water Use Consequences

• Increased green to blue water ratio
• Polluted return flows
• Groundwater over-abstraction
• River regulation

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River Regulation / Fragmentation

• gt45,000 dams above 15 m high
• holding back gt6500 km3 of water
• 15 total global annual river flow
• Major impacts
• inundation
• flow manipulation
• fragmentation

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River Regulation / Fragmentation
Red Heavy Impact Yellow Moderate Impact Green
Little or No Impact White No Large River Basins
Source Nilsson et al, 2005
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Part 2 Climate change the hydro-cycle

• ClausiusClapeyron, water vapour and rainfall
• Aerosols, evaporation and rainfall
• Changes in circulation
• CO2 and plant water-use
• Warming of the cryosphere

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ClausiusClapeyron

• Warmer temperature ? larger water vapour capacity
  
• Upper constraint on hydrological cycle response
  to warming
• Observational evidence that relative humidity has
  remained constant so specific humidity has
  increased

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GCM Precipitation Clausius-Clapeyron
C-C
GCMs
Allen Ingram, 2002

• Precipitation constrained not by warming but by
  troposphere cooling
• CO2 warms troposphere, reduced condensation to
  offset this and maintain energy balance

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GCM Precipitation Clausius-Clapeyron
GCM CO2 vs Control ?T 3.6K (2090s) ?P99
20 ?P99 / ?T 5.5 ? C-C

• Extreme rainfall events occur when all moisture
  in column is rained out
• Appears to be increasing according to C-C

13
Aerosols

• 1960-1980s
• increasing aerosols
• global dimming
• 1990s and 2000s
• decreasing aerosols (Europe and N America)
• global brightening
• Hydrological effects
• Reduced, then increasing evaporation (radiation)
• Reduced, then increased surface warming
• Increased, then decreased upper air warming
• Accelerated recent rainfall increase?
• Factor in recent Sahelian drought
• Uncertain influences on clouds and hence rainfall

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GCM Precipitation Clausius-Clapeyron
Observations
C-C
Wentz et al, 2007
GCMs
Allen Ingram, 2002

• Global brightening warming surface and reduced
  warming of troposphere
• Enables enhanced vertical latent heat transfer
  and release through precipitation

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Changes in Circulation

• Warming climate can lead to shifts in general
  circulation
• Expansion and weakening of Hadley Cell

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Changes in Circulation

• Warming climate can lead to shifts in general
  circulation
• Expansion and weakening of Hadley Cell
• Northward expansion of mid-lat storm tracks
• Warming might also lead to changes in modes of
  variability
• Positive trends in annular modes
• More intense and more frequent El Nino
• Global precipitation might increase, but
  distribution in space and time will vary

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CO2 and Plant Water Use

• CO2 fertilisation effect
• increased CO2 ? more efficient photosynthesis
• plant stomatal openings narrow ? less
  transpiration
• less total evaporation ? more river flow
• This has been detected in river flows, post 1960

Source Gedney et al, 2006
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Warming The Cryosphere

• Mountain glaciers and permafrost
• remnants of water locked away during last ice age
• unprecedented recent mountain glacier retreat
• Rapid increase in runoff in arctic rivers
• increased rainfall
• permafrost melt
• linked to
• AO / NAO
• Temperature

Peterson et al, 2002
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Water scarcity, demand climate change
Current Climate
DIA Demand or withdrawals Q Discharge (river
and shallow groundwater) DIA/Q gt 0.4 high
stress level according to UN/WMO Source
Vorosmarty et al., 2000
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Future Stress Change in DIA/QPopulation Rules,
OK
Source Vorosmarty et al., 2000
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References

• Allen, M. R., and W. J. Ingram (2002),
  Constraints on future changes in climate and the
  hydrologic cycle, Nature, 419, 224-.
• Gedney, N., et al. (2006), Detection of a direct
  carbon dioxide effect in continental river runoff
  records, Nature, 439, 835-838.
• Hu, Y., and Q. Fu (2007), Observed poleward
  expansion of the Hadley circulation since 1979,
  Atmos. Chem. Phys., 7, 5229-5236.
• Lambert, F. H., et al. (2008), How much will
  precipitation increase with global warming?, EOS,
  Transactions, American Geophysical Union, 89,
  193-194.
• Milly, P. C. D., et al. (2002), Increasing risk
  of great floods in a changing climate, Nature,
  415, 514-517.
• Min, S. K., et al. (2008), Human-induced arctic
  moistening, Science, 320, 518-520.
• Oki, T., and S. Kanae (2006), Global Hydrological
  Cycles and World Water Resources
  10.1126/science.1128845, Science, 313, 1068-1072.
• Peterson, B. J., et al. (2002), Increasing river
  discharge to the Arctic Ocean, Science, 298,
  2171-2173.
• Rijsberman, F. R. (2006), Water scarcity Fact or
  fiction?, Agricultural Water Management Special
  Issue on Water Scarcity Challenges and
  Opportunities for Crop Science, 80, 5-22.

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References

• Roderick, M. L., and G. D. Farquhar (2002), The
  cause of decreased pan evaporation over the past
  50 years, Science, 298, 1410-1411.
• Roderick, M. L., et al. (2007), On the
  attribution of changing pan evaporation,
  Geophysical Research Letters, 34.
• Vorosmarty, C. J., et al. 2000 Global Water
  Resources Vulnerability from Climate Change and
  Population Growth. Science, 289 284-288.
  http//www.sciencemag.org/cgi/content/abstract/28
  9/5477/284.
• Wentz, F. J., et al. (2007), How much more rain
  will global warming bring?, Science, 317,
  233-235.
• Wild, M., et al. (2005), From dimming to
  brightening Decadal changes in solar radiation
  at Earth's surface, Science, 308, 847-850.
• Willett, K. M., et al. (2007), Attribution of
  observed surface humidity changes to human
  influence, Nature, 449, 710-U716.
• Wu, P. L., et al. (2005), Human influence on
  increasing Arctic river discharges, Geophysical
  Research Letters, 32, art. no.-L02703.