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.