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Climate Change – 2: Effects on Freshwater Resources

Climate Change – 2: Effects on Freshwater Resources. Human Activities Affect Freshwater Resources. Both quantity and quality. Emissions of greenhouse gases. Terrestrial part of hydrological cycle. Climate. Land Use. Population, life style, economy, technology. Water Resources Management.

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Climate Change – 2: Effects on Freshwater Resources

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  1. Climate Change – 2: Effects on Freshwater Resources

  2. Human Activities Affect Freshwater Resources • Both quantity and quality Emissions of greenhouse gases Terrestrial part of hydrological cycle Climate Land Use Population, life style, economy, technology Water Resources Management Food Demand Water Use

  3. Observed climate-related trends

  4. Current Vulnerabilities of Freshwater Resources and Their Management

  5. Projected Vulnerabilities of Freshwater Resources

  6. Impacts due to increases in temperature, sea level and precipitation variability • Seasonal shift in streamflow • Increase in the ratio of winter to annual flows • Reduction in low flows caused by decreased glacier extent or snow water storage • Sea-level rise will extend areas of salinisationof groundwater and estuaries, decrease in freshwater availability in coastal areas • Increased precipitation variability will increase risks of flooding and drought

  7. Semi-arid and arid areas particularly exposed to impacts of climate change on freshwater • Mediterranean basin, western USA, southern Africa, and north-eastern Brazil) will suffer a decrease in water resources due to climate change • Groundwater recharge will decrease considerably • Effects will be exacerbated by the rapid increase in population and water demand (very high confidence)

  8. Water Quality • Higher water temperatures • Increased precipitation intensity • Longer periods of low flows • Exacerbate water pollution • Impacts on • Ecosystems, • Human health, • Water system reliability • Operating costs

  9. Climate change affects infrastructure as well as water management • Aggravates impacts of other stresses • population growth, changing economic activity, land-use change, and urbanisation • Water demand will grow due to population growth and increased affluence • Large changes in irrigation water demand are likely • Current water management practices are very likely to be inadequate to reduce the negative impacts of climate change on • water supply reliability, flood risk, health, energy, and aquatic ecosystems

  10. Driver - Temperature • Will increase by • 2020s ~ 1°C • 2100 ~ 2 - 4°C • Greatest increases at high northern latitudes and over land • Increases will be stronger in summer than in winter • Sea-level rise will be between 14 and 44 cm within this century (does not take ice sheet melting into account)

  11. Driver - Precipitation • Will increase at high latitudes and in the tropics • e.g., the south-east monsoon region and over the tropical Pacific • Will decrease in sub-tropics • e.g., over much of North Africa and the northern Sahara • Variability will increase

  12. Water Stress • Population at risk of increased water resources stress (A2 scenario): • 2020s 0.5-1.7 billion; • 2050s 1.5-2.0 billion; • 2080s 2.4-3.2 billion • By the 2050s water stress on global land area is projected to • Decrease on 20-29% and • Increase on 62-76% Zbigniew W. Kundzewicz, Sept. 2007

  13. Water Scarcity Zbigniew W. Kundzewicz, Sept. 2007

  14. Floods Zbigniew W. Kundzewicz, Sept. 2007

  15. Water-related Hotspots on Map of Relative Changes in Runoff

  16. Uncertainties • Increase with the length of the time horizon • Near term (e.g., the 2020s), model uncertainties • Longer time horizons, emissions scenario • GCMs subject to uncertainties in the modeling process • Climate projections not easy to incorporate into hydrological impact studies • For the same emissions scenario, different GCMs produce different geographical patterns of change, particularly with respect to precipitation • Agreement with respect to projected changes of temperature is much higher than with respect to changes in precipitation • GCM structure is the largest source of uncertainty, next are the emissions scenarios, and finally hydrological modeling

  17. Some GCM Issues • Most climate change studies consider only changes in precipitation and temperature • Time series of observed climate values are adjusted with the computed change in climate variables to obtain scenarios that are consistent with present-day conditions to minimise the error in GCMs • Mismatch of spatial grid scales between GCMs (typically a few hundred kilometers) and hydrological processes • Techniques to downscale GCM outputs to finer spatial (and temporal) resolution have been developed • Dynamic downscaling - based on links between the climate at large and at smaller scales • Statistical downscaling - using empirical relationships between large-scale atmospheric variables and observed daily local weather variables

  18. Model resolutions as function of spectral truncation 2.8ox2.8o (200 x 300 km) 1.4ox 1.4o (100 x 150 km) 1990’s 2005 2011?

  19. o o 3 x 3

  20. Change in Annual Runoff by 2041 (relative to 1900-70)

  21. Change in Annual Runoff by 2090 (relative to 1980-99)

  22. Adaptation

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