Abstract
The purpose of this research is to investigate the climate change impacts in Maroon Basin, Iran. To investigate the impacts of climate change on rainfall, temperature, and inflow in Maroon Dam, a simulation of four general circulation models (GCMs) was done in three future periods 2021–2040, 2041–2060, and 2061–2080. The results showed that the projected increased temperature would significantly reduce the runoff in the basin, despite the projected increase in rainfall. The most significant decrease of the average inflow to the Maroon Dam Reservoir in the near future of the RCP4.5 and RCP8.5 scenarios in March 24 and 26.4%, the middle future in March 25.4 and 29%, and the far future in March 27 and 30.6%, respectively, is predicted. Also, the MODSIM model simulation results showed that the Maroon Dam Reservoir would face a water resources shortage in the future to provide maximum demands. The average water supply reliability in climate change scenarios showed that the maximum water supply of 85% in the period 2021–2040 and the minimum of 80.4% in 2061–2080 would occur in the RCP4.5 and RCP8.5 scenarios, respectively.
HIGHLIGHTS
To plan for water resources allocation to demands in the Maroon Basin affected by climate change, a combination of SWAT and MODSIM models was used.
It was found that the RCP8.5 scenario will have the most severe water stress and the worst allocation conditions.
Add-on of a water management model to a hydrological model results in a powerful simulation tool that can serve for sustainable river basin management.
INTRODUCTION
Water is a nonrenewable and vital resource that requires efficient management to distribute water resources properly. Nowadays, the effects of climate change worldwide, such as uneven distribution of rainfall, increasing drought frequency and duration, and its negative impact on water resources, are tangible. Climate change can worsen an already existing water shortage as an additional pressure factor in some regions of the world, as it may lead to increased rainfall variability and global warming (Bates et al. 2008). So, the study of the effects of climate change on water resources is much more important than identifying and studying the principles of the climate change phenomenon itself. The Intergovernmental Panel on Climate Change (IPCC 2007) has identified the impact of climate change and its negative effects as one of the main destructive drivers of available water resources management. Since significant changes in the performance of flow networks are caused by the slightest change in hydrological variables, various approaches have been proposed to reduce harmful effects (IPCC 2007). Climate change influences reservoir operations and water availability of reservoirs (Lee et al. 2016) through alterations in precipitation, temperature, and solar radiation (Farinosi et al. 2019; Liu et al. 2020). Due to the scarcity of water resources, the operation of dam reservoirs is of great importance because of the economic value resulting from the optimal use of available water resources, the increasing trend of water demands, and the lack of available water resources (Chhuon et al. 2016). In recent years, the inflow of the Maroon Basin into its reservoir has decreased due to climate change and has created problems in meeting water demands downstream (Zalaki-Badil et al. 2017). Many studies have been conducted to evaluate the optimal operation of dam reservoirs in climatic scenarios and the results showed the inflow to the dam reservoirs would be significantly reduced in the future. In a study, Dahe & Srivastava (2002) defined the water yield model as a multi-efficiency and multi-reservoir model with an acceptable deficit in annual water yield. Their results showed that the water yield model in a multi-reservoir system with single- and multi-objective conditions predicts acceptable flow compared to the simulation model. Abbaspour et al. (2009) investigated the project of Iran's water resources affected by climate change. The results showed that the probability of floods in the northern and western regions of Iran, especially in the Zagros Mountains, will increase due to changing rainfall patterns.
In other words, according to the rainfall pattern in the future, the amount of high-intensity alternate floods in this region will increase. Javadi et al. (2021) used a combination of decision-making models, numerical groundwater modeling, and clustering technique to determine suitable sites for the implementation of an artificial recharge project. This hybrid approach was employed for the Yasouj aquifer located in southwestern Iran. Eini et al. (2020) investigated the development of alternative SWAT-based models for simulating water budget components and streamflow for a karstic-influenced watershed. The results showed that karst conditions and geometry of sinkholes in karst zones did not play a major role in creation of runoff. Rahmani-Rezaeieh et al. (2020) evaluated the impacts of climate change on the floodway and floodway fringe along the Shahrchay River located at Lake Urmia Basin in Iran. The results indicated that the climate model typically underestimates the temperature and precipitation values at the historical period. In addition, a significant decrease in total runoff volume in future periods is expected and the number and magnitude of peak flows would be increased. Jafari et al. (2021) studied fully integrated numerical simulation of surface water–groundwater interactions using SWAT-MODFLOW with an improved calibration tool. The results indicated that the curve number (CN2) and GW hydraulic conductivity (K) parameters have the most significant impact on runoff and GW level simulation. Wu et al. (2023) established a novel social-ecological coupling model to meet the previous coupling coordination degree models that are empirical and very complex, without physical parameters. The research results showed that the model can well reflect changes in vegetation coverage and simplify expression of the coordinated development of social-ecological systems. Xu et al. (2023) evaluated the status of ‘Happy River’ management in the new era of China. The results showed that the follow-up work can be promoted from the aspects of ecological construction, water culture construction, water protection, and social functions. Yang et al. (2023) assessed the effects of climate factors and soil properties on ecosystem C stocks through field investigation across the Loess Plateau. The results highlight that grasslands are more predestined to store C compared with the other ecosystems, and the C stored in roots is substantial and should be considered when assessing C stocks and strongly contributes to soil organic matter formation.
Sharafati et al. (2020) evaluated the quantification and uncertainty of the impact of climate change on river discharge and sediment yield in the Dehbar River Basin in Iran. This study highlights the significant negative impact of climate change on the Dehbar River Basin, with amplification of river flows and sediment concentrations in the wet season and increased water scarcity in the dry season. Yazdandoost & Moradian (2021) studied the impacts of climate change on the streamflow of the Zarrineh River. Results on hydroclimatological changes in Zarrineh River Basin showed that the mean daily precipitation is expected to decrease from 0.94 and 0.96 mm in 2015 to 0.65 and 0.68 mm in 2050 under RCP2.6 and RCP8.5, respectively. In the case of temperature, the numbers change from 12.33 and 12.37 °C in 2015 to 14.28 and 14.32 °C in 2050. Ahn et al. (2009) evaluated the agricultural water supply capacities for the Geum River Basin in South Korea by performing a water balance analysis and considering a network of agricultural irrigation facilities using the MODSIM model. Emami & Koch (2017) evaluated the impacts of climate and demand changes on the dam operation by comparing future and historical MODSIM simulated average water budget and supply/demand ratio for the three CESM model scenarios. The results showed that the region will face more intensive water shortages in the future, owing to climatic change and increasing demands. Nguyen et al. (2022) evaluated the impacts of future changes in land use, climate, and downstream water demands on the reservoir water supply performance. The results showed that the reservoir performance can be improved by adjusting water allocation policies and best management practices in the basin. Although many studies investigated the impacts of climate change on the water cycle (Abbaspour et al. 2009), fewer studies have focused on the evaluation of the water supply of a river basin due to the impacts of climate change (Akbari et al. 2022).
The Maroon Reservoir is the main structure in the region providing water for downstream demands. In addition, the reservoir cannot meet all water demand requirements during this period. Under uncertain future, the existing operational rule curve needs to be updated due to reduced storage and considerable change in water demands. The overall aim of this study was (a) to use an adaptive optimization approach to project the range of reliability of the reservoir under possible scenarios and (b) to suggest options to improve the water supply of the reservoir.
This study was conducted in four steps:
- (1)
Calibration and validation of the SWAT model and do a monthly runoff comparison of two hydrostations in Maroon Basin;
- (2)
Prediction of the temperature and rainfall by integrating four GCM CMIP5 models in baseline and future periods and RCP4.5 and 8.5 scenarios with statistical downscaling;
- (3)
Prediction of the inflow to the reservoir in baseline and future periods; and
- (4)
Water balance analysis and assessment of watershed's water supply reliability to achieve adaptive operation of Maroon reservoir in the current situation and future periods using the MODSIM model.
MATERIAL AND METHODS
Case study area
The Maroon Basin is located in the southwestern part of Iran in the Zagros mountainside with an area of 3,808 km2. This river is created by connecting the Shabliz, Ludab, and Saqaveh branches, and it reaches the Maroon Dam Reservoir after a distance of 120 km. The Maroon reservoir has a storage capacity of 1,274 Mm3, with a water surface area of approximately 2,500 ha. The area of the basin is located in a semi-arid climatic region. The minimum altitude in this area is 300 and the maximum altitude is 3,489 m above sea level. The annual rainfall, evaporation, and average temperature in the basin are approximately 520 mm, 2,730 mm, and 26 °C, respectively. The wet season often lasts from November to May, with a maximum of 130 mm in December, and varying seasonally in other months. The geology of Maroon Basin consists of outcrops, sandstone, conglomerate, and alternation of colored marl and silty limestone.
Evaluation of climate change
Characteristics of four models selected from the CMIP5 collection for the present study
No. . | Model . | Institution/Country . | Spatial resolution . |
---|---|---|---|
1 | GFDL-CM3 | Geophysical Fluid Dynamics Laboratory, USA | 2.5 × 2.0 |
2 | EC_EARTH | EC_EARTH consortium published at Irish Centre for High-End Computing, Netherlands/Ireland | 1.28 × 2.5 |
3 | Hadgem2-ES | Met Office Hadley Centre, UK | 1.875 × 1.25 |
4 | Miroc5 | The Atmosphere and Ocean Research Institute (The University of Tokyo), National Institute for Environmental Studies, and Japan Agency for Marine-Earth Science and Technology, Japan | 1.41 × 1.39 |
No. . | Model . | Institution/Country . | Spatial resolution . |
---|---|---|---|
1 | GFDL-CM3 | Geophysical Fluid Dynamics Laboratory, USA | 2.5 × 2.0 |
2 | EC_EARTH | EC_EARTH consortium published at Irish Centre for High-End Computing, Netherlands/Ireland | 1.28 × 2.5 |
3 | Hadgem2-ES | Met Office Hadley Centre, UK | 1.875 × 1.25 |
4 | Miroc5 | The Atmosphere and Ocean Research Institute (The University of Tokyo), National Institute for Environmental Studies, and Japan Agency for Marine-Earth Science and Technology, Japan | 1.41 × 1.39 |
SWAT and MODSIM models
Characteristics of the stations in the study area
Station type . | Station name . | Latitude . | Longitude . | Altitude (m) . | Description . |
---|---|---|---|---|---|
Hydrometric and Climatology | Idenak | 30.95 | 50.42 | 560 | |
Hydrometric | Dehno | 30.97 | 50.87 | 1,340 | |
Hydrometric | Tange-Takab | 30.68 | 50.33 | 280 | Downstream of the dam reservoir |
Hydrometric | Cham-Nezam | 30.75 | 49.92 | 190 | Downstream of the dam reservoir |
Synoptic | Dehdasht | 30.78 | 50.58 | 793 | |
Synoptic | Behbahan | 30.60 | 50.21 | 313 |
Station type . | Station name . | Latitude . | Longitude . | Altitude (m) . | Description . |
---|---|---|---|---|---|
Hydrometric and Climatology | Idenak | 30.95 | 50.42 | 560 | |
Hydrometric | Dehno | 30.97 | 50.87 | 1,340 | |
Hydrometric | Tange-Takab | 30.68 | 50.33 | 280 | Downstream of the dam reservoir |
Hydrometric | Cham-Nezam | 30.75 | 49.92 | 190 | Downstream of the dam reservoir |
Synoptic | Dehdasht | 30.78 | 50.58 | 793 | |
Synoptic | Behbahan | 30.60 | 50.21 | 313 |
Details of resolution and time period of the collected data
Station name . | Parameter . | Data collection period . | Jan . | Feb . | Mar . | Apr . | May . | Jun . | Jul . | Aug . | Sep . | Oct . | Nov . | Dec . |
---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|
Idenak | Flow (m3/s) | 1999–2018 | 63.4 | 76.2 | 86.7 | 87.1 | 48 | 26.4 | 16.4 | 11.7 | 9.8 | 12 | 18.3 | 51.5 |
Dehno | Flow (m3/s) | 1999–2018 | 16.9 | 19.5 | 24.8 | 22.3 | 9.5 | 3.9 | 2 | 1.5 | 1.1 | 1.5 | 2.4 | 11.7 |
Tange-Takab | Flow (m3/s) | 1999–2018 | 45.3 | 47.5 | 57.4 | 41.4 | 26.8 | 23.4 | 31.8 | 34.5 | 32.1 | 29.9 | 29.7 | 30.3 |
Cham-Nezam | Flow (m3/s) | 1999–2018 | 56.6 | 52.8 | 55.2 | 35.8 | 24.2 | 22.2 | 26.9 | 26.6 | 25.6 | 25.8 | 29.1 | 41.4 |
Idenak | Rainfall (mm) | 1999–2020 | 126.2 | 90.6 | 53 | 52.4 | 11.8 | 0 | 0 | 2 | 1.2 | 0 | 52.5 | 129.3 |
Dehdasht | Rainfall (mm) | 1999–2020 | 114.1 | 80.3 | 45.9 | 43.6 | 12.5 | 2.1 | 0 | 2.5 | 1 | 0 | 45.6 | 105.3 |
Behbahan | Rainfall (mm) | 1999–2021 | 67.6 | 42.6 | 21.1 | 26.1 | 8.5 | 0 | 0 | 0 | 0.6 | 1 | 28.1 | 85.2 |
Idenak | Temperature (°C) | 1999–2018 | 12.4 | 13.2 | 17.3 | 23.6 | 30.8 | 38.3 | 41 | 40.8 | 37.6 | 30.2 | 21.5 | 14.2 |
Dehdasht | Temperature (°C) | 1999–2021 | 13.1 | 13.8 | 18.3 | 24.7 | 32.4 | 40.1 | 43.2 | 42.7 | 39.6 | 31.6 | 22.7 | 14.8 |
Behbahan | Temperature (°C) | 1999–2021 | 14.5 | 15.1 | 20.1 | 27 | 35.6 | 43.9 | 47.4 | 46.8 | 43.4 | 34.6 | 24.9 | 16.2 |
Idenak | Evaporation (mm) | 1999–2019 | 47 | 61 | 89 | 149 | 247 | 388 | 468 | 455 | 373 | 264 | 130 | 63 |
Maroon Dam | Reservoir storage (Mm3) | 1999–2019 | 490.4 | 545.7 | 589.2 | 623.4 | 697.7 | 714.7 | 671.7 | 600.6 | 522.4 | 447.8 | 431.2 | 427.3 |
Station name . | Parameter . | Data collection period . | Jan . | Feb . | Mar . | Apr . | May . | Jun . | Jul . | Aug . | Sep . | Oct . | Nov . | Dec . |
---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|
Idenak | Flow (m3/s) | 1999–2018 | 63.4 | 76.2 | 86.7 | 87.1 | 48 | 26.4 | 16.4 | 11.7 | 9.8 | 12 | 18.3 | 51.5 |
Dehno | Flow (m3/s) | 1999–2018 | 16.9 | 19.5 | 24.8 | 22.3 | 9.5 | 3.9 | 2 | 1.5 | 1.1 | 1.5 | 2.4 | 11.7 |
Tange-Takab | Flow (m3/s) | 1999–2018 | 45.3 | 47.5 | 57.4 | 41.4 | 26.8 | 23.4 | 31.8 | 34.5 | 32.1 | 29.9 | 29.7 | 30.3 |
Cham-Nezam | Flow (m3/s) | 1999–2018 | 56.6 | 52.8 | 55.2 | 35.8 | 24.2 | 22.2 | 26.9 | 26.6 | 25.6 | 25.8 | 29.1 | 41.4 |
Idenak | Rainfall (mm) | 1999–2020 | 126.2 | 90.6 | 53 | 52.4 | 11.8 | 0 | 0 | 2 | 1.2 | 0 | 52.5 | 129.3 |
Dehdasht | Rainfall (mm) | 1999–2020 | 114.1 | 80.3 | 45.9 | 43.6 | 12.5 | 2.1 | 0 | 2.5 | 1 | 0 | 45.6 | 105.3 |
Behbahan | Rainfall (mm) | 1999–2021 | 67.6 | 42.6 | 21.1 | 26.1 | 8.5 | 0 | 0 | 0 | 0.6 | 1 | 28.1 | 85.2 |
Idenak | Temperature (°C) | 1999–2018 | 12.4 | 13.2 | 17.3 | 23.6 | 30.8 | 38.3 | 41 | 40.8 | 37.6 | 30.2 | 21.5 | 14.2 |
Dehdasht | Temperature (°C) | 1999–2021 | 13.1 | 13.8 | 18.3 | 24.7 | 32.4 | 40.1 | 43.2 | 42.7 | 39.6 | 31.6 | 22.7 | 14.8 |
Behbahan | Temperature (°C) | 1999–2021 | 14.5 | 15.1 | 20.1 | 27 | 35.6 | 43.9 | 47.4 | 46.8 | 43.4 | 34.6 | 24.9 | 16.2 |
Idenak | Evaporation (mm) | 1999–2019 | 47 | 61 | 89 | 149 | 247 | 388 | 468 | 455 | 373 | 264 | 130 | 63 |
Maroon Dam | Reservoir storage (Mm3) | 1999–2019 | 490.4 | 545.7 | 589.2 | 623.4 | 697.7 | 714.7 | 671.7 | 600.6 | 522.4 | 447.8 | 431.2 | 427.3 |
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RESULTS
Climate change based on the GCM outputs
Bias-corrected temperature (a), rainfall (b), and changes in the future projected monthly temperature (c), rainfall (d) in Maroon Basin under climate change.
Bias-corrected temperature (a), rainfall (b), and changes in the future projected monthly temperature (c), rainfall (d) in Maroon Basin under climate change.
Calibration, validation, and sensitivity analysis of the SWAT model
SWAT model parameters calibrated and adjusted values
No . | Parameter . | Description . | Initial range . | Calibrated value . |
---|---|---|---|---|
1 | CN2 | SCS runoff curve number | (−0.752)–(−0.263) | −0.489 |
2 | ALPHA_BF | Baseflow alpha factor (days) | (0.624)–(0.865) | 0.635 |
3 | GW_DELAY | Groundwater delay (days) | (5.236)–(39.965) | 26.58 |
4 | HRU_SLP | Average slope steepness | (0.332)–(0.717) | 0.501 |
5 | RCHRG_DP | Deep aquifer percolation fraction | (0.623)–(0.895) | 0.799 |
6 | SLSUBBSN | Average slope length | (12.301)–(41.442) | 21.725 |
7 | CH_K2 | Effective hydraulic conductivity in main channel alluvium | (32.204)–(108.634) | 67.23 |
8 | SOL_AWC | Available water capacity of the soil layer | (−0.425)–(0.091) | −0.182 |
9 | SOL_K | Saturated hydraulic conductivity | (−0.05)–(0.599) | 0.439 |
10 | SOL_BD | Moist bulk density | (0.455)–(0.899) | 0.512 |
11 | SMTMP | Snow melt base temperature | (−1.325)–(2.925) | −0.923 |
12 | SMFMN | Minimum melt rate for snow during the year (occurs on winter solstice) | (3.652)–(5.425) | 4.223 |
13 | REVAPMN | Threshold depth of water in the shallow aquifer for ‘return’ to occur (mm) | (189.225)–(291.333) | 217.44 |
14 | ESCO | Soil evaporation compensation factor | (0.245)–(0.672) | 0.404 |
15 | SFTMP | Snowfall temperature | (3.325)–(6.121) | 4.132 |
16 | ALPHA_BNK | Baseflow alpha factor for bank storage | (0)–(0.179) | 0.043 |
17 | LAT_TTIME | Lateral flow travel time | (0)–(38.43) | 18.275 |
18 | PLAPS | Rainfall lapse rate | (88.423)–(139.322) | 131.025 |
19 | TLAPS | Temperature lapse rate | (−5.732)–(−0.79) | −4.223 |
20 | PCPMM | The average amount of rainfall falling in the month (mm/dd) | (0.122)–(0.498) | 0.351 |
No . | Parameter . | Description . | Initial range . | Calibrated value . |
---|---|---|---|---|
1 | CN2 | SCS runoff curve number | (−0.752)–(−0.263) | −0.489 |
2 | ALPHA_BF | Baseflow alpha factor (days) | (0.624)–(0.865) | 0.635 |
3 | GW_DELAY | Groundwater delay (days) | (5.236)–(39.965) | 26.58 |
4 | HRU_SLP | Average slope steepness | (0.332)–(0.717) | 0.501 |
5 | RCHRG_DP | Deep aquifer percolation fraction | (0.623)–(0.895) | 0.799 |
6 | SLSUBBSN | Average slope length | (12.301)–(41.442) | 21.725 |
7 | CH_K2 | Effective hydraulic conductivity in main channel alluvium | (32.204)–(108.634) | 67.23 |
8 | SOL_AWC | Available water capacity of the soil layer | (−0.425)–(0.091) | −0.182 |
9 | SOL_K | Saturated hydraulic conductivity | (−0.05)–(0.599) | 0.439 |
10 | SOL_BD | Moist bulk density | (0.455)–(0.899) | 0.512 |
11 | SMTMP | Snow melt base temperature | (−1.325)–(2.925) | −0.923 |
12 | SMFMN | Minimum melt rate for snow during the year (occurs on winter solstice) | (3.652)–(5.425) | 4.223 |
13 | REVAPMN | Threshold depth of water in the shallow aquifer for ‘return’ to occur (mm) | (189.225)–(291.333) | 217.44 |
14 | ESCO | Soil evaporation compensation factor | (0.245)–(0.672) | 0.404 |
15 | SFTMP | Snowfall temperature | (3.325)–(6.121) | 4.132 |
16 | ALPHA_BNK | Baseflow alpha factor for bank storage | (0)–(0.179) | 0.043 |
17 | LAT_TTIME | Lateral flow travel time | (0)–(38.43) | 18.275 |
18 | PLAPS | Rainfall lapse rate | (88.423)–(139.322) | 131.025 |
19 | TLAPS | Temperature lapse rate | (−5.732)–(−0.79) | −4.223 |
20 | PCPMM | The average amount of rainfall falling in the month (mm/dd) | (0.122)–(0.498) | 0.351 |
Summary of the monthly time step calibration and validation of the SWAT model
Station . | Idenak . | Dehno . |
---|---|---|
Calibration | ||
NS | 0.62 | 0.57 |
R2 | 0.66 | 0.61 |
r-factor | 0.73 | 0.65 |
p-factor | 0.73 | 0.67 |
PBIAS (%) | 11.2 | 8.9 |
Validation . | ||
NS | 0.58 | 0.5 |
R2 | 0.69 | 0.62 |
r-factor | 0.66 | 0.63 |
p-factor | 0.7 | 0.64 |
PBIAS (%) | 10.3 | 9.1 |
Station . | Idenak . | Dehno . |
---|---|---|
Calibration | ||
NS | 0.62 | 0.57 |
R2 | 0.66 | 0.61 |
r-factor | 0.73 | 0.65 |
p-factor | 0.73 | 0.67 |
PBIAS (%) | 11.2 | 8.9 |
Validation . | ||
NS | 0.58 | 0.5 |
R2 | 0.69 | 0.62 |
r-factor | 0.66 | 0.63 |
p-factor | 0.7 | 0.64 |
PBIAS (%) | 10.3 | 9.1 |
Comparison of the simulated vs. observed monthly runoffs in Idenak and Dehno hydrostations in the calibration phase.
Comparison of the simulated vs. observed monthly runoffs in Idenak and Dehno hydrostations in the calibration phase.
Comparison of the simulated vs. observed monthly runoffs in Idenak and Dehno hydrostations in the validation phase.
Comparison of the simulated vs. observed monthly runoffs in Idenak and Dehno hydrostations in the validation phase.
Climate change effects on the inflow to the Maroon Dam
Percent difference in the simulated and observed inflow under climate change.
Simulation of water consumption in the current situation
Overview of the simulated network of the Maroon Basin in MODSIM: (a) current situation and (b) future situation.
Overview of the simulated network of the Maroon Basin in MODSIM: (a) current situation and (b) future situation.
Time series of the observed vs. simulated streamflow in Tange-Takab and Cham-Nezam hydrostations downstream of the dam.
Time series of the observed vs. simulated streamflow in Tange-Takab and Cham-Nezam hydrostations downstream of the dam.
The potable of Mansouriyeh, Behbahan, Aghajari, Omidiyeh, and environmental, industrial, and agricultural of north Behbahan (7,050 ha), south Behbahan (7,550 ha), Jayezan and Fajr (6,400 ha), and traditional (cultivated area of 534 ha) are the demands in the simulated network. To execute the MODSIM model, the monthly time series of the mentioned demands from 2001 to 2018 was used. The allocation priorities in this model are potable, environmental, industrial, and agricultural demands, respectively. Also, the agricultural return flow was evaluated at 15–20%.
Variation of the Maroon reservoir storage in the current situation.
Average water supply and demand in Maroon Basin's current situation.
Simulation of water consumption in the climate change condition
Watershed's water supply reliabilities in climate change condition.
Average water supply and shortage in Maroon Basin in climate change condition.
Cultivation pattern to stabilize the agricultural area and the current reliability.
Cultivation pattern to stabilize the agricultural area and the current reliability.
Discussion
The average annual temperature in the scenarios of RCP4.5 and RCP8.5 will increase in all months of future periods compared to the baseline period. The temperature increases in the pessimistic scenario of RCP8.5 are more than in the RCP4.5 scenario, which is similar to the findings of Azari et al. (2016). Long-term monthly changes in average temperature indicate that the most significant increase in temperature will occur in the winter months. This is despite the fact that in all months of this season the highest rainfall will be in the Maroon Basin. Based on the results of the sensitivity analysis of the SWAT model, the parameter of infiltration CN2 in average humidity conditions (CN2) had the greatest effect on the outflow of the basin. Due to the mountainous study area, SMTMP and SMFMN showed more sensitivity than other parameters, which is similar to the findings of Tuo et al. (2018), Rahman et al. (2013), Shafiei Motlagh et al. (2018), and Eslamian et al. (2018). The results of forecasting the inflow in the two scenarios showed that the increase in temperature would have a more significant effect and efficiency in reducing the flow rate efficiency, despite the increase in rainfall in the area. The average flow from January to December will decrease in the three future periods and all two scenarios compared to the baseline period. These results were similar to the findings of Maghsood et al. (2019) and Zalaki-Badil et al. (2017). In these climatic conditions, increasing winter temperatures will reduce snow storage in the heights of this basin and expect more water shortage problems in the future compared to the baseline period. The inflow to the Maroon Dam Reservoir will be the most reduced in the RCP8.5 scenario. The water requirement of plants and evapotranspiration will increase with global warming. The first reason is that evapotranspiration requires energy, and as the climate warms, more energy is needed to carry out this process, which in turn reduces the river flow and inflow to the dam reservoir. The second reason is that the decrease in flow in spring and winter shifts the growing season to winter and prolongs the sowing time. In recent years, the dominant crops of this basin and land preparation for cultivation have been driven to late winter. It has been determined that this trend will continue in the future with more intensity.
Variation in temperature, rainfall, inflow, and water supply under climate change compared to the current situation in the Maroon Basin.
Variation in temperature, rainfall, inflow, and water supply under climate change compared to the current situation in the Maroon Basin.
CONCLUSION
In this research, a combination of SWAT and MODSIM models was used to plan for water resources allocation to demands in the Maroon Basin affected by climate change. To investigate the effect of climate change on basin temperature and rainfall, four GCMs were performed in the two climatic scenarios, RCP4.5 and RCP8.5, over the following three periods: near (2021–2040), middle (2041–2060), and far (2061–2080). The downscaling of rainfall and temperature data in the two scenarios was done using the LARS-WG model. Long-term monthly changes in average temperature indicate that the most significant increase in temperature will occur in the winter months. This is despite the fact that in all months of this season, the highest rainfall will be in the Maroon Basin. The Maroon Dam inflow was simulated using the SWAT hydrological model, and calibrated and validated against the monthly flow at the Idanak and Dehno hydrostations. The NSE indices at Idanak and Dehno hydrostations were 0.62 and 0.57 for the calibration and 0.58 and 0.5 for the validation stages. Then, the rainfall and temperature data were entered into the SWAT model to simulate the inflow to the dam for the following three periods. The most significant decrease of the average inflow to the Maroon Dam Reservoir in the near future of the RCP4.5 and RCP8.5 scenarios in March 24 and 26.4%, the middle future in March 25.4 and 29%, and the far future in March 27 and 30.6% is predicted, respectively. In the last step, the inflow to the Maroon Dam Reservoir in baseline and future conditions was used as one of the important inputs of the MODSIM model. At first, modeling was done for the current situation (2002–2018), and the amount of water allocated to each demand was specified. Using water supply reliability, the allocation process in this period was evaluated, and the allocation of water resources was predicted for the future. By comparing the average water supply reliability in the current situation (96.6%) and climate change scenarios, it was found that the RCP8.5 (2061–2080) scenario with 80.4% will have the most severe water stress and the worst allocation conditions. In this research, an attempt has been made to maintain the cultivated area and water supply reliability in the current situation by changing the cultivation pattern and replacing crops with low water requirements. This study also shows that the add-on of a water management model to a hydrological model results in a powerful simulation tool that can serve for sustainable river basin management and the output can be used further to support better water decision-making systems.
FUNDING
No funds, grants, or other support were received.
ETHICS APPROVAL
This research does not contain any studies with human participants or animals performed by any of the authors.
AUTHORS' CONTRIBUTIONS
All authors contributed to the study's conception and design. Material preparation, data collection, and analysis were performed by M.M. and checked by M.S. The first draft of the manuscript was written by M.M. and edited by M.S. and A.S. All authors read and approved the final manuscript.
DATA AVAILABILITY STATEMENT
Data cannot be made publicly available; readers should contact the corresponding author for details.
CONFLICT OF INTEREST
The authors declare there is no conflict.