Materials and Methods
The method used in this study: (1) generating SWAT of the basin, (2) the
model calibration by using the FACT (Fast Auto Calibration Tool; Ozdemir
and Leloglu 2018) (3) examining the effects on climate change water
resources in the basin by using the Representative Concentration
Pathways, RCP 4.5, and RCP 8.5 climate change scenarios, (4) predicting
the effects of climate change on streamflow rate and NPS pollution loads
by using different land-use scenarios; conversion of shrubland to the
forest, conversion of agricultural areas to the forest, and (5) the
assessment of the results by using statistical analysis (6) determining
the effects of climate and land-use changes on water resources in the
basin to provide further research on the subject in the future.
Study Area
The Namazgah dam is between
40055’-41004’ north longitude and
30000’- 30025’east latitude in the
Marmara region, Turkey (Fig. 1). The dam was constructed on the Namazgah
river to provide water demands such as irrigation, drinking, etc., of
villages and towns of Izmit and Korfez districts and tourist settlements
at the Black Sea coast. The area of the basin is 100.64
km2. The land in the basin is predominantly used for
agriculture activities, especially for hazelnut production and pasture
in the basin. The recorded mean annual rainfall, evaporation, maximum
and minimum temperature values are 805 mm/a, 744.3 mm/a, 250C and 5 0C, respectively. The mean
annual flow rate of the Namazgah river is measured as 48.88
hm3. The planning amount of water to be supplied as
drinking and domestic water from the Namazgah Dam of 2014, 2030, and
2045 is 8.695.399, 11.300.658, and 12.965.044 m3/year,
respectively.
SWAT
The primary elements of the SWAT model are weather, hydrology, soil
temperature and properties, plant growth, nutrients, pesticides,
bacteria and pathogens and land management. In SWAT, sub-basins are
generated by dividing the basin based on the topography. Hydrologic
response units (HRUs) for each sub-basin, the smallest unit in the
model, are created from equivalent combinations of land use and soil
type. The calculation of hydrologic processes is made at the HRU level
and happens in two steps: (1) calculating flow and sediment, nutrients,
bacteria, and pesticides loads at each HRUs, and then combining
area‐weighted HRU‐level loadings to the sub-basin level; and (2) routing
loadings from each sub-basin through the channel/stream network (Gassman
et al. 2007).