Discussion

IPCC (2018) indicated that global warming was predicted to increase by 1.5 °C by 2050’s compared with the present situation. Hydrological cycle and water quality will be affected by global warming (Anand et al. 2018). The generation of proper water management plans depends on interdisciplinary approaches and modeling studies of direct and indirect effects of climate change on drinking water resources (Qiu et al. 2019). Water management strategies for drinking water basins must be developed based on climate change’s effect on water quality and quantity (Garnier and Holman 2019). It is difficult to meet good quality water demand for public health since the world population until 2050 will increase 9,7 million, so this will increase world water demand by 20-30 % (UNESCO, 2019). Land uses-covers and climate change are the main factors of water quality and quantity degradation globally (Giri and Qiu 2016; Su et al. 2016). The preparation of better water management policies is based on both land use-cover and climate change impacts on non-point pollution sources and streamflow (Mello et al. 2018). Although domestic legislation has been conducted to provide sustainable drinking water management in many countries, measures in that legislation haven’t been determined based on adaptation to climate change and for understanding the patterns of water use under different land-use/cover policies (Wang et al. 2018; Clerici et al. 2019; Trolle et al. 2019). In Turkey, based on the Regulation on Protection of Drinking and Utility Water Basins (PDUWB 2017), site-specific drinking water management plans have been generated. However, these studies don’t include climate and land use- cover change policies. Moreover, although these studies cover many measures, especially the restriction of agricultural activities and protection of forest areas, the effects of these measures on streamflow and NPS have not been examined. This study is an example of land-use/cover and climate change effects on streamflow and NPS to generate accurate water resources management. Climate change scenarios, RCP 4.5 and RCP 8.5, and land-use scenarios, conversion of shrubland to the forest and conversion of agricultural areas to the forest, were combined to show their impacts on flow rate and NPS pollutants to generate future proper water management plans. Study results show that conversion of agricultural areas to the forest under RCP 8.5 has more impacts on streamflow and NPS pollutants. This situation indicates that land-use planning and restrictions in drinking water basins require examining land-use/cover and climate change effects on water resources and NPS pollutants to protect drinking water resources for public human health.
Moreover, this study also shows that modeling studies and statistical assessments of modeling results are important to evaluate these effects while studying these effects on water resources and NPS pollutants since combining modeling and statistical assessments give whether or no significant effects of these changes.