Sustainable Water Resources Management. Wolfgang Kinzelbach IfU, ETH Zürich

Transcription

1 Sustainable Water Resources Management Wolfgang Kinzelbach IfU, ETH Zürich

2 Contents Sustainability: Definition Common non-sustainable practices Some conclusions

3 Sustainable water management Practice, which avoids irreversible and quasi-irreversible damage to the resource water and the natural resources connected to it conserves in the long term the capability of the resource water to perform its services (including ecological services)

4 Includes: Sustainable Development in a broader sense - conservation of the environment, - economic efficiency, and - social justice Even more difficult to define! Easier to say what is not sustainable than what is

5 What does non-sustainable mean in the context of water resources? A practice is non-sustainable, if it leads into a crisis in the long run Non-sustainability shows in - Depletion of a finite resource, which cannot be sustituted (e. g. groundwater, soil, biodiversity) - Accumulation of substances to dangerously high concentrations (e. g. salts, nutrients, heavy metals) - unfair allocation of a resource which leads to conflict (e. g. upstream downstream problem) - Failure of institutions - Explosion of costs

6 The most serious problems of nonsustainability in the water sector on a global scale:

7 Depletion of aquifers 1/4 of withdrawals non-renewable 40% of irrigated agriculture affected by declining groundwater levels

8 Main cause for overpumping of aquifers: Large scale irrigation with groundwater Examples: Ogallalla Aquifer, USA North China Plain Karoo Aquifers, South Africa Aquifers of the Arabian Peninsula Nord Sahara Aquifer System (SASS) Ganges valley India Typical rate of water table decline 1 to 3 m/a,

9 Decrease of low flows of rivers Even large rivers become seasonal, lakes dry up, upstream-downstream conflicts increase. Most tragic example: Lake Aral Base flow = groundwater discharge

10 Examples Yellow river (1997 no flow for 220 days over a length of 700 km, total storage volume of reservoirs in catchment larger than mean annual flow) Lake Aral (dried/drying up) Euphrates and Tigris (GAP Project) Nile (Salt water intrusion increases) Jordan (Israel-Syria-Jordan-Palestine-Libanon) and many others Main problem: Agriculture in upstream evaporates water which is lacking in the downstream (consumptive use). Water power causes much less losses. It makes flow more homogeneousover the year.

11 Loss of wetlands and other water- dependent ecosystems Area halved globally between 1900 and 2000 Water surface of wetland is basically groundwater table

12 Loss of wetlands Loss of essential biodiversity Right of nature to use water Economic benefits of wetlands often underestimated Alternative use often not sustainable In Europe: Rehabilitation programs

13 Soil salinization 80 Mio. of 260 Mio. ha irrigated area more or less affected Usually caused by too high groundwater table

14 Causes Problem of soil salinization Globally about 80 Mio. ha of crop land are affected in some way or other by salinization For comparison: 1500 Mio. ha total crop land, of which 260 Mio. ha are irrigated natural Water, Salts Water vapour irrigated Water, Salts Without drainage: Accumulation of salts Groundwater table rise, capillary rise, evaporation of groundwater, salt deposition

15 Pollution of water bodies with large residence time (e. g. aquifers) with persistent or recycleable pollutants For all Problems: Intensification by climate change possible Sea water intrusion Monterey Bay

16 Pollutants in groundwater Bacteria and viruses Nitrate, pesticides Mineral oil hydrocarbons Chlorinated hydrocarbons Chromium, PAH,... Reversibility for persistent pollutants only after very long times

17 Why is river pollution not a problem of sustainability? Reversibility has been demonstrated in European rivers e. g. Rhine, Thames (residence time of water small) and lakes: e.g. Swiss lakes Required: Substantial investments and political will But: Eutrophication of lakes can be a long term problem because of nutrient recycling Example: Taihu in China

18 How to check for sustainability? Build a model of the system, capable of describing the past Fix system parameters and boundary conditions Define human stresses or management decisions Run system model to time t Check whether solution exists with a final state being acceptable with respect to predefined indicators: environmental, health, economic, social

19 Type of sustainable solution Certainly not like this: Time Not necessarily static Maybe quasi-periodic! Time Time

20 General conclusions Sustainability is a difficult concept, which has to be defined anew in every situation. Sustainability in water systems is most often related to groundwater. China and Central Asia present all types of non-sustainable practices Given sufficient system knowledge the model-based analysis of a regional system with respect to sustainability is feasible To reach sustainability globally may only be possible when world population has decreased Tasks to be solved by you are tremendous!