5. Surface Water

Turkey is a country with considerable water resources in a region where water is a strategic element due to its scarcity. With the increase in the population and demand, water scarcity has accelerated, making water a more vital element. Due to the considerably large size of the country and to the spatial and temporal uneven distribution of water resources, water demand in some regions exceeds the available water for a period of time that creates a water shortage. Surface water hydrology in Turkey is a great challenging problem as it has the greatest share (80%) in the water potential of the country. The total annual surface flow is 186.6 billion m^3, almost all born from the river basins within the territory of Turkey and harvested with the rainfall-runoff coefficient of 0.37 from the 574.0 mm annual rainfall. Surface water resources of Turkey are divided between 25 river basins; most stay within the country. There are also transboundary river basins where Turkey is either the upstream country or the downstream country. Among the river basins, the Euphrates-Tigris has the highest contribution, which is almost 1/3 of the surface water potential of Turkey. The northeastern part of Turkey receives the highest precipitation while the least amount of rainfall falls on Central Anatolia. A quite high number of hydrometric gauges have been established to record the quantity and quality of water; however, more are emerging, considering the topographical and geographical diversity in Turkey, to observe such hydrometeorological variables as streamflow, precipitation, evaporation, snow depth, etc. Due to the great spatial variability in the hydrometeorological conditions, some regions in Turkey are flood-prone while others can be affected by extreme droughts. Trend analysis has shown that extremes in the streamflow become more pronounced with larger maxima and lower minima than before. Also, lakes are important fresh water bodies for domestic use as well as irrigation, farming, industry, fisheries, etc. Water level in many lakes however decreases so that the availability of water in the lakes are under risk. Integrated water resources development strategies are needed at country-scale to balance the demand with the available water, considering also the decreasing trend in water availability and the increasing trend in the demand.