oa Adaptive water resources management under global environmental change: Examples from a small semiarid Mediterranean municipal district

Climate change is expected to have a significant impact on the hydrologic cycle, creating changes in freshwater resources. Globally, the supply of freshwater far exceeds human requirements. However, by the end of the 21st century, these requirements will begin to approach the total available water. Regionally, water demand for various sectors already exceeds supply. This will most probably get worse with increasing population and societies' changing water demands. On the other hand, many experts believe that we are currently (2013) on the 4°C path and the 2°C target has become unrealistic because it would require reductions in greenhouse gas emissions that would be too deep and too abrupt to be sustained by the world's economy. Thus, policymakers, businesses and other decision-makers need to plan ahead for adaptation to changes in climate associated with higher levels of global warming. This requires coherent information on the new conditions which must be adapted to, and the consequences of different courses of adaptation action. The Mediterranean has been described as one of the main climate change "hot-spots", with recent simulations showing a collective picture of substantial drying and warming. This effect appears more pronounced during warm periods, when the seasonal decrease of precipitation can exceed control climatology by 25-30%. State-of-the-art climate model projections combined with local hydrological modeling for the island of Crete, Greece, for the period 1970-2100 reveals an overall decreasing precipitation trend (Fig 1.) which, combined with a temperature rise (Fig. 1), leads to substantial reduction of water availability (Fig. 2). Due to projected climate changes the region may face intense droughts that will intensify regional environmental problems. The changes in magnitude and frequency of precipitation will cause severe problems to the water availability which is currently being achieved through traditional methods such as groundwater exploitation, surface water storage and water transport amongst neighboring regions. An alternative method to tackle these water shortages is the exploitation of treated wastewater in the water demanding sector of irrigation which can be proved to be a low-cost and technically feasible solution. The present study deals with the evaluation of water resources availability and wastewater reuse perspectives in the water resources management for the small Mediterranean municipal district of Akrotiri, in northwest Crete. Alternative measures, like transportation of water from distant springs, effluent reuse and desalination are compared via a simple cost-benefit analysis. Wastewater reclamation and reuse cost is favorably compared to the existing practice of surface or/and groundwater use and is far more cost effective than desalination. Moreover, wastewater reuse for irrigation has the main advantage of coastal protection, i.e., zero effluent discharge in coastal areas, while it provides a water source that is not dependent on climate variability. Quantitative analysis provides the data required to develop appropriate strategies on water shortage mitigation through effluent reuse, under a changing climate and increased water demand perspectives.