Introduction

Water is a vital resource for the survival of not only human population but also almost all ecosystems. Therefore, access to safe freshwater is regarded as a universal human right [1]. Although water is globally abundant, 97% of the whole is

Department of Geological Engineering, Middle East Technical University, 06531 Ankara, Turkey e-mail: [email protected]

O. Yagbasan

Department of Geography Education, Gazi University, 06570 Ankara, Turkey saline water in oceans. Fresh water constitutes only the remaining 3%, 69% of which is attained in ice-caps and glaciers [2]. These numbers reveal the importance of groundwater, constituting 30% of all fresh water, as a main source of fresh water on which at least two billion people worldwide depends for domestic, industrial and agricultural activities.

As a part of the hydrologic cycle, groundwater is a renewable resource, yet it is not infinite. Rate of the renewal is limited to the rate of the replenishment, and closely related to the rate of depletion. Ever increasing demand on groundwater has led to overexploitation of the aquifers and degradation of groundwater quality. Consequently, the time when abundant supplies of water were readily available for development at low economic, social and environmental cost has passed. Now, the great challenge facing the world is to cope with the impact of economic growth on the environmental processes [3]. Moreover, climate change will exacerbate ground-water related problems by producing reduced recharge rates in some areas, more reliance on groundwater resources due to decrease in reliability of surface waters, farther inland penetration of saltwater intrusion in response to both sea-level rise and excessive groundwater extraction and deterioration of groundwater quality by increased flushing of urban and agricultural waste due to more frequent flooding. These problems emerged the concern about the sustainable management of ground-water so that it is not depleted while the increasing demand is satisfied.

The most important pressure that climate change will exert on groundwater resources will be the changing rate of recharge which is closely related to the changes in precipitation. Therefore, following similar trends with precipitation, groundwater recharge rates will either decrease or increase for different geographical regions. For instance, IPCC reported that a more than 70% decrease in groundwater recharge is computed in north-eastern Brazil, southwest Africa and along the southern rim of the Mediterranean Sea, whereas more than 30% increase in groundwater recharge is computed in Sahel, the Near East, northern China, Siberia and the western USA [4]. However, the most dramatic impacts of changing recharge rates on groundwater resources is foreseen at the locations where precipitation and accordingly recharge is expected to decrease. Decreasing recharge rates will definitely affect the quantity of the available groundwater resources, while the quality of the groundwater resources, especially in coastal regions, will be threatened by the saltwater intrusion and salini-sation of groundwater due to the increased evapotranspiration [5]. Consequently, decreasing recharge rates will also enhance the impacts of processes which have already been observed, such as saltwater intrusion. Hence, this study aims to assess the impacts of decreasing recharge rates on management of groundwater resources using a hypothetical coastal aquifer system under various pumping scenarios.

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