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

3. Growth in Water Use 6.5 times increase in global water withdrawals from 1900-2000 5.5 times increase in area of irrigated agriculture 3.6 times increase in global population Approximately 66% of global water withdrawals are for agriculture, over 90% in many developing countries6.5 times increase in global water withdrawals from 1900-2000 5.5 times increase in area of irrigated agriculture 3.6 times increase in global population Approximately 66% of global water withdrawals are for agriculture, over 90% in many developing countries

4. 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

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

7. River Regulation / Fragmentation >45,000 dams above 15 m high holding back >6500 km3 of water 15% total global annual river flow Major impacts inundation flow manipulation fragmentation Inundation: destroys terrestrial ecosystems and eliminates turbulent reaches, disfavoring lotic biota cause anoxia, greenhouse gas emission, sedimentation, and an upsurge of nutrient release in new reservoirs resettlement associated with inundation can result in adverse human health effects and substantial changes in land use patterns Flow manipulation: hinder channel development, drain floodplain wetlands, reduce floodplain productivity decrease dynamism of deltas or cause delta subsidence, and may cause extensive modification of aquatic communities Fragmentation prevent dispersal and migration of organisms Inundation: destroys terrestrial ecosystems and eliminates turbulent reaches, disfavoring lotic biota cause anoxia, greenhouse gas emission, sedimentation, and an upsurge of nutrient release in new reservoirs resettlement associated with inundation can result in adverse human health effects and substantial changes in land use patterns Flow manipulation: hinder channel development, drain floodplain wetlands, reduce floodplain productivity decrease dynamism of deltas or cause delta subsidence, and may cause extensive modification of aquatic communities Fragmentation prevent dispersal and migration of organisms

8. River Regulation / Fragmentation Over 50% of large, river basins are fragmented or regulatedOver 50% of large, river basins are fragmented or regulated

9. Part 2: Climate change & the hydro-cycle Clausius–Clapeyron, water vapour and rainfall Aerosols, evaporation and rainfall Changes in circulation CO2 and plant water-use Warming of the cryosphere

10. Clausius–Clapeyron 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

11. GCM Precipitation & Clausius-Clapeyron Precipitation constrained not by warming but by troposphere cooling CO2 warms troposphere, reduced condensation to offset this and maintain energy balance

12. GCM Precipitation & Clausius-Clapeyron 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

14. GCM Precipitation & Clausius-Clapeyron Global “brightening” warming surface and reduced warming of troposphere Enables enhanced vertical latent heat transfer and release through precipitation

15. Changes in Circulation Warming climate can lead to shifts in general circulation Expansion and weakening of Hadley Cell

16. 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

17. 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

18. 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

19. Water scarcity, demand & climate change

20. Future Stress: Change in DIA/QPopulation Rules, OK

21. 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.

22. 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/289/5477/284]. 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.