Qualitative assessment of Darband River water resources under climate change conditions using the TODIM multi-criteria decision-making method

Abstract
Objective: Rivers constitute vital freshwater resources and play an indispensable role in sustaining human life and aquatic ecosystems. In recent decades, however, many rivers have progressively become recipients of municipal wastewater, industrial effluents, and agricultural runoff. This shift in water resource utilization has led to severe deterioration of river water quality and has exerted significant pressure on aquatic ecosystems. The primary objective of the present study is to assess the water quality of the Darband River using the Water Quality Index (WQI). Subsequently, the relative importance of four key factors is evaluated and ranked within the WQI framework using the TODIM multi-criteria decision-making (MCDM) method.
Method: For this purpose, monthly data on precipitation, temperature, total dissolved solids (TDS), electrical conductivity (EC), pH, and sulfate (SO₄) over the statistical period of 1988–2005 were analyzed to determine the current status of river water quality. To investigate the potential impacts of climate change on river water quality, future climatic variables were projected using the GFDL-ESM2G model for precipitation and the MIROC-ESM-CHEM model for temperature under three representative concentration pathways (RCP 2.6, RCP 4.5, and RCP 8.5). Regression relationships were then established between the climatic and hydrological variables influencing river discharge and the key water quality parameters. Based on the projected river discharge for the period 2030–2047, water quality conditions were estimated under each emission scenario, and the corresponding parameters were subsequently ranked using the TODIM method.
Results: The results indicate noticeable variations in water quality indices across different scenarios, highlighting the differential influence of individual water quality parameters.
Conclusion: These findings provide a robust basis for evaluating the relative contribution of key parameters to water quality improvement and offer valuable insights for river basin management and climate-adaptive water quality planning.
 
 
 
English Extended Abstract
Introduction
Rivers, as vital sources of water supply, play a fundamental and undeniable role in human life. These water resources are not only essential for agricultural purposes, such as irrigating farmlands and providing food for human populations, but also for drinking and industrial uses. In recent years, many rivers have become primary destinations for discharging urban wastewater, industrial pollutants, and agricultural runoff. This shift in perspective regarding the use of water resources has led to serious problems in river water quality and has significantly impacted aquatic ecosystems. This study aims to assess the water quality of the Darband River using a water quality index. Subsequently, the weights of four factors will be examined and ranked in the water quality index using the TODIM multi-criteria decision-making method.
 
Method
In this section, the research process is described. Initially, after collecting baseline data and information for the study area, the performance of climate models is evaluated based on the Fifth Assessment Report of the IPCC. Subsequently, the relevant climatic variables for future periods will be simulated. Following this, the water quality status in both present and future conditions will be examined using the Water Quality Index, and finally, the influential qualitative parameters impacting water quality will be ranked, and their weights will be adjusted.
In this study, the relevant climatic variables were simulated by using the GFDL-ESM2G model for precipitation and the MIROC ESM-CHEM model for temperature in the baseline period (1988–2005) and near future (2030–2047) under three scenarios: RCP2.6, RCP4.5, and RCP8.5. Then, water quality in the baseline and future periods was assessed using the Iran Water Quality Index (WQIIR), the World Health Organization Water Quality Index (WQIWHO), and the Schuler classification. Finally, using the TODIM multi-criteria decision-making method, effective parameters were ranked based on water quality indices.
The entropy-Shannon weighting method was employed for weighting the criteria in this study. The entropy-Shannon method represents the dispersion of values in decision-making; the greater the degree of dispersion, the higher the level of deviation. The study area for this research is the Darband River Basin.
 
Results
This section presents the results of changes in water quality during the baseline and future periods, as well as weighting methods and the ranking of options, which represent water quality indices for the study area.
The relationships between water quality parameters and climatic factors such as temperature and precipitation were examined during the baseline period. The findings indicate an inverse relationship between rainfall and EC, TDS, and SO₄. This suggests that an increase in precipitation leads to a reduction in EC and dissolved solids in surface waters. By substituting the projected values of minimum and maximum temperatures and precipitation into the derived relationships, the future values of each water quality parameter can be estimated.
Based on the regression relationships obtained for each parameter, their values were calculated under baseline conditions and different scenarios to assess the water quality of the Darband River using the WQIIR, WQIWHO, and Schuler classification indices. The results indicate that the water quality under baseline conditions is in a good state, and forecasts suggest that, for all three climate change scenarios, the water quality will remain in good condition in both indices. Since the coefficients and relative weights differ between the two indices, the magnitude of the indices also differs, with WQIWHO having higher values.
A decision matrix was formulated based on two criteria: minimizing WQIWHO and maximizing WQIIR, along with four options—TDS, EC, pH, and SO₄—that each represent the relative weight of water quality parameters. To determine the weight of the criteria, the entropy of each criterion, its degree of deviation, and finally, its weight were calculated. The findings indicate that changes in options have a greater impact on maximizing WQIIR compared to minimizing WQIWHO.
The results also show that reducing EC has a greater impact on the criteria due to its higher relative weight compared to other parameters, and its reduction has a more significant effect on improving water quality.
 
Conclusion
The findings regarding climate change in the Darband River Basin indicate that maximum temperature under future scenarios will experience a significant increase compared to baseline conditions. Similarly, precipitation levels are also projected to show an upward trend in the future relative to the baseline period. Consequently, water quality parameters will also change. The results reveal that the river's water quality was in a favorable condition during the baseline period, and it is expected to maintain good quality in the future.
In the final stage, using the TODIM multi-criteria decision-making method, four selected alternatives were ranked under climate change conditions. The results indicate that water quality indices vary across different alternatives, and these findings can be used to determine the impact of each quality parameter on improving water quality. However, it is recommended that, for a more comprehensive assessment, the impact of other pollutants on this river should also be studied to develop a specific index for it.