Assessment of the Water Resources Carrying Capacity of Anzali Wetland Using a Combined AHP-Entropy Weighting Method and Forward cloud model

Introduction

For the sustainable development of the socio-economic economy, water resources are not only an important limiting factor but also play an irreplaceable "carrier" role. "Carrying capacity" is a term derived from ecology that refers to the limitation of the maximum number of individuals in specific environmental conditions. Water Resources Carrying Capacity (WRCC) is the support capacity of water resources for the livelihood of the region's population and socio-economic development. Due to the differences in water resource systems, socio-economic conditions, and ecological environmental settings in various regions and natural conditions, the assessment of WRCC does not follow a consistent pattern across different geographical areas, making the evaluation of WRCC a complex issue. The aim of assessing and analyzing WRCC is to determine the relationship between limited water resources and population, the environment, and economic development.

Wetlands play a pivotal role in sustainable development as a vital resource. With increasing population and economic growth, the pressure on water resources is rising. The Water Resource Carrying Capacity is defined as the ability of a water system to support human activities. In this study, considering the significance of Anzali wetland, which is being destroyed alongside the advancement of urbanization processes as one of the natural ecosystems, the water resources carrying capacity of Anzali wetland is being evaluated.

Materials and Methods

To evaluate the water resources carrying capacity, initially, the water resource system of the region was first modeled by using the system dynamics method and VENSIM software. Based on the modeling results, eight evaluation indicators were defined to assess the WRCC of Anzali Wetland, considering three subsystems: population, water resources, economy, and environment. Subsequently, based on the modeling results, indices were defined for each subsystem with the aim of assessing the water resources carrying capacity of Anzali wetland, with a total of 8 indices considered for evaluation. The weighting of the indices was done using the combined AHP-Entropy method .In order to accurately assess the carrying capacity of water resources, aligning the results with the actual situation of the region, and considering the water resources of Anzali Wetland, the current water resources and consumption in the Fumanat study area (located upstream of Anzali Wetland), the economic and environmental conditions of the region, and the use of water resources in the area, the evaluation indices were divided into four levels based on the standards for grading water resource carrying capacity indices in previous research. These levels are: I (loadable), II (weak), III (critical), and IV (extremely critical). Finally, using a fuzzy model and determining the membership degrees of the indices at each evaluation level and for each year, the water resources carrying capacity index of Anzali wetland was calculated for different evaluation levels over a 10-year period.

Results and Discussion

To determine the initial weights of the evaluation indices, expert opinions were utilized, and acceptable results were obtained using the Analytic Hierarchy Process (AHP) method and Consistency Ratio (CR). Subsequently, composite weights were calculated by combining the AHP weights with entropy, with the highest weight attributed to the indicator of water supply and demand ratio of the wetland (C7), followed by indicators such as the quality of input water resources and the impact of agricultural gross production. The results of this section demonstrate that the final composite weights are more realistic as the entropy method enhances the shortcomings of the AHP method, thereby improving the accuracy of the evaluation.

The results of the Water Resources Carrying Capacity (WRCC) assessment indicate a decreasing trend in the water resources carrying capacity of Anzali wetland between the years 1391 to 1400, shifting its capacity from level II (Weak) to level IV (Super Critical). The highest capacity is associated with the year 1391, while the lowest capacities are allocated to the years 1393, 1394, and 1400. Examination of the obstacle factors revealed that surface and groundwater resources significantly impact the water resources carrying capacity of the wetland, with several indicators from the water resources subsystem identified as the main obstacle factors in this regard. These constraints pose challenges to improving the wetland's capacity, and the increase or decrease of these resources, especially under environmental and economic conditions, significantly influences the wetland's status

Conclusion

The results showed that the WRCC of the wetland had a decreasing trend during the study period and had reached a supercritical state. The most important factors affecting the reduction in carrying capacity were identified as the shortage of surface and groundwater resources and the poor quality of water entering Anzali Wetland.The overall findings of the investigations indicate that Anzali wetland has been in critical and super-critical conditions in recent years, highlighting the necessity for planning to improve its situation. Considering the obstacle factors identified in this study, efforts can be directed towards planning and managing the wetland to move towards a more desirable state.