Conclusion

The protective regulations in drinking water basins in Turkey have tried to provide sustainable water management. However, water management policies prepared based on the legislation don’t contain land use-landcover and climate change impacts on flow rate and NPS pollutants. The main source of water quality degradation is NPS pollutions rather than point source pollution. This study presents the preliminary results to determine the impact of land use and climate change on streamflow rate and NPS pollutants in the Namazgah dam basin to develop successful sustainable watershed management plans. According to the RCP 4.5 and RCP 8.5 scenarios, a decrease in the monthly average total amount of precipitation is estimated between 2021-2090. The highest rainfall is expected in the summer period in 2022-2090 in contrast to between 1979 and 2014. An increase of approximately 0.49oC is expected in average monthly temperatures 2021-2090 compared to 1979-2014 concerning the RCP 8.5 scenario, while a decrease of 0.35 oC is expected concerning the RCP 4.5 scenario. Corresponding modeled stream flow rates based on RCP 4.5 and RCP 8.5 scenarios for 2021-2099 period, are 0.716 and 0.672 m3/sec, respectively. These values show significant decrease in flow rates of the Namazgah river in the future (the mean annual flow rate was 1.90 m3/sec between 1991-2007). The amount of the monthly average of TN and TP loads in the basin for the years 1991-2007 were 41379.953 and 8427.269 kg, respectively. However, these were predicted as 49892.916 TN, 13200.190 TP; 47211.188 TN, 12602.330 TP kg based on RCP 4.5 and RCP 8.5 for 2021-2099 period. According to both climate change scenarios, a decrease in the predicted flow rates will cause an increase in TP and TN loads. When examining land-use change scenarios, according to RCP 4.5, similar results were obtained for both land-use change scenario. However, according to RCP 8.5, conversion of farmland to forest has more effect on an increase in NPS loads and a decrease in flow velocities than conversion of shrublands to the forest.