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Groundwater in big cities, use, consequences, impacts of climate change and response options Karen G. Villholth Groundwater Specialist, Senior Researcher GEUS, Geological Survey of Denmark and Greenland Copenhagen, Denmark FAU Conference 2000 Copenhagen Business School, Denmark, May 15, 2008 Groundwater withdrawal, cubic km/year Groundwater development in selected countries India 250 USA China 200 Bangladesh Pakistan Mexico 150 W.Europe Tunisia 100 South Africa Sri Lanka Vietnam 50 Spain Ghana 0 1940 Ref: Shah, 2004 1960 1980 2000 Importance of GW for cities • Groundwater is the main source of domestic- • • potable water supply in most European countries (Water Economy Prospects for 1990 and 2000, 1982) In general, GW is the primary source for domestic water supply and hence significant for most cities Quantity-wise, GW use for cities is less than the use in agriculture Reasons and advantages of using groundwater for cities • Surface water exhausted or polluted • New drilling and pumping technology • Groundwater is generally of a good, reliable and • constant quality and temperature suitable for drinking water with no or little pre-treatment Groundwater can be developed incrementally and with less capital investment Feature Groundwater resources and Groundwater aquifers Surface water resources and Surface water reservoirs HYDROLOGICAL CHARACTERISTICS Storage volume Large to very large small to moderate Resource areas relatively unrestricted restricted to water bodies Flow velocities very low moderate to high Residence times decades/centuries weeks/months Drought propensity generally low generally high Evaporation losses low and localized high for reservoirs Resource assessment high cost and significant uncertainty lower cost and often less uncertainty Abstraction impacts delayed and dispersed immediate Natural quality generally (but not always) high variable Pollution vulnerability variable natural protection largely unprotected Pollution persistence often extreme mainly transitory Public perception of resource unconnected and replenishable limited, aesthetic Development cost generally modest often high Style of development mixed public and private largely public Knowledge of resource and importance Sparse, use underestimated, impacts disregarded well-developed, use well-documented SOCIO-ECONOMIC FACTORS Groundwater flow and occurrence Importance of groundwater,1 Importance of groundwater, 2 Importance of groundwater, 3 Importance of groundwater, 3 Importance of groundwater, 4 Impact in response to change Pre-development Post--development (T1) Post--development (T2) Effect on riparian vegetation Example from Dhaka, Bangladesh Δ=22% Δ=30m over 30 years GWL decline, example from China Δ=20m over 35 years Hydrograph depicting water-table elevations beneath Luancheng Agro-Ecological Research Station (Chinese Academy of Sciences), Luancheng County, Hebei Province, 1974-2002. Dramatic changes of depression cones in Cangzhou m m 6-1973 2-1981 GWL decline, example from Chicago Saltwater intrusion • Inflow of saltwater into freshwater aquifer • Origin of saltwater: – Seawater in coastal areas – Geological saline deposits in deeper formations – Influx or accumulation from irrigated agriculture In coastal areas there is a natural balance between salt and freshwater ground surface phreatic water table sea fresh groundwater zone on i s u f f of di saline groundwater impervious layer GW withdrawal in coastal auifers Subsidence Subsidence, impacts • Gives problems for infrastructure, buildings, pipelines • Flooding and drainage patterns changed • Causes secondary GW contamination from breakage of underground pipes and tanks What is subsidence? Before After Example of subsidence, San Joaquin Valley GWL Landsurface level Relation btw. subsidence and GWL decline Example of subsidence, Texas Groundwater pollution sources GW pollution risk Vulnerability high, but load is low Load is high, but vulnerability is low high Urbanization • Generally, urbanization decreases the recharge to aquifers (pavements, storm water drainage) • However, depending on the primary source of water supply and the means of discharging wastewaters, GWLs may be affected differently Climate change • There is accumulating evidence that the climate is changing on a global scale • Exact effects not known as well as the speed, extent and local distribution of them • Some effects seem inevitable: – Water level rises due to global warming – More variability and unpredictability in climate and more ‘extreme’ events – Dry regions becoming drier • Effects compounded by other human influences (e.g. • intensive water exploitation) Most vulnerable areas: Arid areas, big coastal cities, large tropical deltas Climate change on GW in cities • GW can be a drought prevention strategy but only to a certain extent • GW over-abstraction and flooding can occur at the same time • Energy intricately linked to GW exploitation • CC exacerbate existing problems of GW Disaster management Post-Modern Water Balance Increased Pumpage to Meet Domestic, Increased Water Demand for Agriculture, Agricultural, Industrial and People and Ecosystems Ecosystem Demands Precipitation/Recharge Precipitation Change Ground Water Water Contamination Contamination Cost-Effective Water Increased Valuation/ Treatment and Economic Conservation Breakpoints Technologies Virtual Water Imports And Exports Transboundary Disputes Flows Changes in Water Availability Saltwater intrusion Number of wells Total abstraction Sustainable level of ressource development with acceptalbe impacts under present conditions time 0 1 2 3 4 Baseline situation Incipient stress an Significant stress Unstable development Stable development Availability and accessibility of adequate quality groundwater greatly exceeds small dispersed demand Growth of aquifer pumping, but only few local conflicts between neighbouring abstractors Abstraction expanding rapidly with impacts on natural regime and strong dependence of stakeholders on ressource Excessive abstraction with irreversible aquifer deterioration and stakeholder conflicts High-level of abstraction, but sound balance between stakeholder interests and ecosystem needs Registration of wells required, together with maps of occurrence of usable resources Simple management tools (e.g. appropriate well-spacing according to aquifer properties) Regulatory framework needed, based on comprehensive assessment Regulatory framework with demand managemnt and/or artificial recharge urgently needed Integrated management with high-level of user self-regulation, aquifer monitoring and assessment Some response options • • • • • • • • More focus on GW, monitoring, permits, GW mgt. as an integral part of IWRM Combine demand and supply mgt. Awareness of general public => genuine stakeholder participation in groundwater protection Capacity building => Research into mgt. => informed mgt. Advocacy at the policy level => importance of GW acknowledged and incorporated into policies and institutions Climate change a driver for GW emphasis No blanket policy