Assessment of the LULCC in the study has been carried out on a larger scale than the lake watershed itself. Gediz River Basin, which includes the Lake Marmara watershed, has been assigned as the wider analytical extent for the LULCC analyses. Within the LCM analyses that were conducted with respect to the historical LULC data in the period 2000–2012, a total of 23 transitions have been addressed (Table 3). Out of all these considered transitions, 3 have been chosen for the development of the sub-model: (1) agriculture to urban; (2) vineyards or others to urban and (3) agriculture to barren. The chosen transitions are highly related to the objectives set forth for the presented study, mainly targeting simulations for possible disturbances on agriculture. These disturbances are indeed very significant on different layers, such that the agricultural activities mainly have considerable impact on economic, social and environmental levels. While the sprawl of agriculture could indicate any reduction in quantity and quality aspects for water resources, withdrawal of agricultural lands possibly causes social and economic pressures.
The Multi-Layer Perceptron (MLP) method has been employed to determine the transition potentials between the historical LULC maps and then this has been followed by the future prediction for the year 2018 as part of the validation process. As the validation approach for the LULCC model, Relative Operating Characteristic (ROC) analysis has been utilized (Fig. 7). Calculated area under the curve (AUC) of the total ROC curve yielded the value of 72% in a way to represent fair success rate in the sense of modelling goodness-of-fit statistics (Gorunescu 2011).
Table 5
Land cover transitions between 2000 and 2012 for the extent of Gediz River Basin
Transition No | Transition Name | Area (km²) | Transition No | Transition Name | Area (km²) |
1 | Agriculture to Barren | 1.10 | 13 | Vineyards to Forest | 0.24 |
2 | Agriculture to Pasture | 0.41 | 14 | Vineyards to Urban | 0.57 |
3 | Agriculture to Urban | 12.60 | 15 | Pasture to Agriculture | 0.95 |
4 | Agriculture to Water | 0.60 | 16 | Pasture to Barren | 6.44 |
5 | Barren to Agriculture | 0.63 | 17 | Pasture to Forest | 1.93 |
6 | Barren to Pasture | 0.48 | 18 | Pasture to Vineyards | 0.22 |
7 | Barren to Urban | 1.63 | 19 | Pasture to Urban | 2.52 |
8 | Forest to Agriculture | 1.20 | 20 | Pasture to Transportation | 0.93 |
9 | Forest to Barren | 0.41 | 21 | Pasture to Water | 0.56 |
10 | Forest to Vineyards | 0.32 | 22 | Urban to Agriculture | 0.18 |
11 | Forest to Pasture | 58.53 | 23 | Water to Agriculture | 2.06 |
12 | Forest to Urban | 0.38 | | | |
After the validation process, future prediction for the year 2050 has been carried out (Fig. 8). Results of the LULCC analyses depict that there is considerable increase in urban sprawl and in the rate of agricultural withdrawal in the Lake Marmara extent (Table 6).
Table 6
Land cover type totals and differences through 2000 and 2050
Cover Type | Area (km2) |
2000 | Difference (%) | 2012 | Difference (%) | 2018 | Difference (%) | 2050 |
Agriculture | 119.72 | -18.09 | 98.06 | -0.06 | 98.00 | -7.81 | 90.35 |
Barren | 5.99 | -69.76 | 1.81 | 76.43 | 3.19 | -43.32 | 1.81 |
Forest | 23.20 | -23.94 | 17.65 | -13.14 | 15.33 | 15.13 | 17.65 |
Vineyards | 7.41 | 258.40 | 26.54 | 0.00 | 26.55 | 0.01 | 26.55 |
Pasture | 87.11 | 12.41 | 97.92 | 0.41 | 98.32 | -0.41 | 97.92 |
Urban | 2.25 | 47.32 | 3.32 | 17.68 | 3.90 | 182.22 | 11.01 |
Water | 60.98 | -0.19 | 60.86 | 0.00 | 60.86 | 0.00 | 60.86 |
Wetlands | 3.89 | 12.48 | 4.38 | 0.00 | 4.38 | 0.00 | 4.38 |
The visual comparison of the LULCCs in Lake Marmara watershed through the years between 2000 and 2050 has been presented in the Fig. 9. Noticeable changes have been marked for indication. As given in the Table 6, urban sprawl and withdrawal of barren land are to be expected until 2050 in the Lake Marmara watershed.
According to the LULCCs, area-weighted average values of CNs of the sub-basins have been calculated for the year 2012 and 2050 in order to be utilized as input in the HEC-HMS hydrologic model (Table 7). Since the changes in the cover types are relatively small in the extent of the lake watershed, area-weighted averages of the CNs also differ slightly in the period 2012–2050.
From the hydrological perspective of the projected figures for LULCCs, the runoff rate for the year 2050 has been calculated in accordance with the RCP 8.5 climate scenario (Fig. 10). According to the results, runoff values are estimated to increase by almost 6% until the year 2050 with much clearer differences between the maximum and minimum monthly averages computed periodically.
This result may indicate that the lake ecosystem and surrounding social and economic assets can be prone to increased threats due to the appearance of bigger variation to be observed between the monthly flows throughout the year, by increasing the significance of much improved control operations for water supply and a more detailed planning of water allocation schemes between the water dependent sectors of the lake ecosystem.
Table 7
Area percentages of the cover types and area weighted average CN values of the sub-basins through 2012–2050
Year | 2012 |
Subbasin | SB1 | SB2 | SB3 | SB4 | SB5 | SB6 |
Agriculture | 33,18 | 10,39 | 5,18 | 3,21 | 27,94 | 17,55 |
Barren | 1,53 | 0,28 | 0,00 | 0,00 | 0,00 | 0,00 |
Forest | 8,07 | 0,47 | 0,00 | 2,43 | 6,65 | 0,00 |
Vineyards | 14,24 | 0,91 | 1,24 | 0,46 | 9,65 | 0,00 |
Pasture | 52,83 | 7,52 | 8,69 | 11,45 | 12,14 | 5,01 |
Urban | 2,29 | 0,00 | 0,13 | 0,13 | 0,48 | 0,28 |
Water | 0,01 | 0,01 | 0,06 | 0,00 | 0,01 | 0,11 |
Wetlands | 1,77 | 0,28 | 2,24 | 0,00 | 0,00 | 0,00 |
CN | 66,33 | 70,41 | 71,59 | 61,48 | 67,79 | 74,50 |
Year | 2050 |
Subbasin | SB1 | SB2 | SB3 | SB4 | SB5 | SB6 |
Agriculture | 30,25 | 10,39 | 4,52 | 2,93 | 26,38 | 15,35 |
Barren | 1,53 | 0,28 | 0,00 | 0,00 | 0,00 | 0,00 |
Forest | 8,07 | 0,47 | 0,00 | 2,43 | 6,65 | 0,00 |
Vineyards | 14,24 | 0,91 | 1,24 | 0,46 | 9,66 | 0,00 |
Pasture | 52,83 | 7,52 | 8,69 | 11,45 | 12,14 | 5,01 |
Urban | 5,21 | 0,00 | 0,79 | 0,41 | 2,04 | 2,49 |
Water | 0,01 | 0,01 | 0,06 | 0,00 | 0,01 | 0,11 |
Wetlands | 1,77 | 0,28 | 2,24 | 0,00 | 0,00 | 0,00 |
CN | 66,53 | 70,41 | 71,90 | 61,61 | 68,01 | 75,26 |
For the water balance simulations; observed and modelled precipitations, evaporation rates calculated according to the Meyer evaporation method and the observed demands have been considered. Since the lake region is located more below the average groundwater level of the river basin and thus the lake area greatly locates on saturated soils, infiltration losses have been considered negligible specifically in the lake watershed. No inflows from the Gediz River to the lake have also been accounted in hydrologic simulations since 2011 that associates to the year when the Gördes Dam started operating and allowing no diversion from the regulator structure that previously supplied flows to the lake.
Generated water balance simulations take count of mainly the satisfaction of the minimum volume requirement for addressing the environmental need of the lake ecosystem, assumed to be in a quantity of 23.47 hm3, which associate to the minimum volume storage amount determined by the Waterware software for these environmental requirements for the future dry year scenario. Time to fail and monthly water deficit volumes to satisfy the environmental needs have been calculated accordingly in the generated simulations as in Table 8 through the Excel software by following the water balance equation given in Eq. 3.1.
\({S}_{t}={P}_{t}+{S}_{t-1}-{E}_{t}-{D}_{t}\) (Eq. 3.1)
where St, Pt, St−1, Et and Dt denote the end of month-t storage volume (hm3), the total precipitation in month-t (hm3), the end of month-(t-1) storage volume (hm3), the total evaporation in month-t (hm3) and the total water demand in month-t (hm3), respectively.
According to the results of the water balance simulations, two outcomes are apparent; every scenario model has failed to satisfy the volume required to meet the environmental needs of the lake and the LULCC in the case of Lake Marmara has very little significance on the rainfall-runoff process compared to the climate change. Among the scenarios structured, M1.7, M1.8 and M1.9 give similar results by indicating their relatively better performances than the rest of the scenarios. In these scenarios, while the water volume deficit increases up to the total amount of environmental need, time to fail is 8th month, namely August. On the other hand, scenarios M3.1, M3.2 and M3.3 associate to the worst cases where the volume deficit increases up to almost 5 times the required volume for the environmental need and the time to fail decreases to 6th month, namely June. Deficiency volumes have been plotted below in the Figs. 10 and 11 for irrigated, 50% irrigated and non-irrigated scenario conditions, respectively.
Table 8
Monthly water deficit volumes (hm3) to satisfy the environmental needs of the Lake Marmara
Month | M1.1 | M1.2 | M1.3 | M1.4 | M1.5 | M1.6 | M1.7 | M1.8 | M1.9 |
1 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | 0 |
2 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | 0 |
3 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | 0 |
4 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | 0 |
5 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | 0 |
6 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | 0 |
7 | -9.1 | -4.6 | -9.1 | 0 | 0 | 0 | 0 | 0 | 0 |
8 | -41.8 | -39.2 | -41.8 | -22.3 | -19.8 | -22.3 | -2.9 | -0.3 | -2.9 |
9 | -61.3 | -58.7 | -61.3 | -39.9 | -37.3 | -39.9 | -18.5 | -15.9 | -18.5 |
10 | -67.3 | -68.1 | -67.3 | -45.5 | -46.2 | -45.5 | -23.6 | -24.4 | -23.6 |
11 | -67.1 | -69.8 | -67.1 | -45.3 | -48.0 | -45.3 | -23.5 | -26.2 | -23.5 |
12 | -60.5 | -61.0 | -60.5 | -38.7 | -39.2 | -38.7 | -16.9 | -17.4 | -16.9 |
Month | M2.1 | M2.2 | M2.3 | M2.4 | M2.5 | M2.6 | M2.7 | M2.8 | M2.9 |
1 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | 0 |
2 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | 0 |
3 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | 0 |
4 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | 0 |
5 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | 0 |
6 | -15.2 | -9.4 | -15.2 | -8.9 | -3.1 | -8.9 | -2.5 | 0 | -2.5 |
7 | -50.5 | -46.0 | -50.5 | -37.3 | -32.8 | -37.3 | -24.1 | -19.6 | -24.1 |
8 | -83.1 | -80.6 | -83.1 | -63.7 | -61.1 | -63.7 | -44.2 | -41.7 | -44.2 |
9 | -102.7 | -100.1 | -102.7 | -81.3 | -78.7 | -81.3 | -59.9 | -57.2 | -59.9 |
10 | -108.6 | -109.4 | -108.6 | -86.8 | -87.6 | -86.8 | -65.0 | -65.8 | -65.0 |
11 | -108.4 | -111.2 | -108.4 | -86.6 | -89.4 | -86.6 | -64.8 | -67.6 | -64.8 |
12 | -101.8 | -102.4 | -101.8 | -80.0 | -80.6 | -80.0 | -58.2 | -58.8 | -58.2 |
Month | M3.1 | M3.2 | M3.3 | M3.4 | M3.5 | M3.6 | M3.7 | M3.8 | M3.9 |
1 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | 0 |
2 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | 0 |
3 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | 0 |
4 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | 0 |
5 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | 0 |
6 | -23.2 | -17.4 | -23.2 | -16.9 | -11.1 | -16.9 | -10.5 | -4.7 | -10.5 |
7 | -58.5 | -54.0 | -58.5 | -45.3 | -40.8 | -45.3 | -32.1 | -27.6 | -32.1 |
8 | -91.1 | -88.6 | -91.1 | -71.7 | -69.1 | -71.7 | -52.3 | -49.7 | -52.3 |
9 | -110.7 | -108.1 | -110.7 | -89.3 | -86.7 | -89.3 | -67.9 | -65.3 | -67.9 |
10 | -116.6 | -117.4 | -116.6 | -94.8 | -95.6 | -94.8 | -73.0 | -73.8 | -73.0 |
11 | -116.5 | -119.2 | -116.5 | -94.7 | -97.4 | -94.7 | -72.9 | -75.6 | -72.9 |
12 | -109.9 | -110.4 | -109.9 | -88.1 | -88.6 | -88.1 | -66.3 | -66.8 | -66.3 |