haned eskandari damaneh

Nowadays, an unprecedented need is felt for considering groundwater quantity and quality in water resource management plans in all ecosystems. The availability of adequate and proper water resources for various uses is an important factor of sustainable development in arid and semi-arid regions such as Minab Plain in the south of Iran. Given the climatic conditions of this plain and the overuse of groundwater tables for various uses, it was decided to investigate the variations in the quantity and quality of groundwater tables and simulate their future trend to find out their impact on the rate of desertification and land degradation. There are diverse traditional methods to assess the quantity and quality of underground water, but they are not economical in time and cost. Today, modern groundwater quantity and quality determination methods have mostly resolved this problem to be informative about the future trend of these variations. Hydrological models were used to estimate groundwater variations trends. Different scenarios were applied to plan and manage these irreparable resources in the future. The present study evaluates groundwater tables' quantitative and qualitative variations using the MGS software package and the Modular Three-Dimensional Finite-Difference Groundwater Flow Model (MODFLOW) code.  The variations of these irreparable resources were simulated in Minab plain to study the rate of desertification in the past, present, and future. Finally, the managerial approaches were proposed to prevent the further depletion and quality loss of groundwater tables in this plain and adopt strategies tailored to determine the desertification rate in the future.

For this research, data of hydrology and geology of the Minab Plain aquifer were supplied by Iran Water Resources Management Company for 2003-2018. After data collection, GMS10.5 was employed to study and model groundwater resources and their future condition. First, the variations in groundwater quantitative and qualitative parameters in Minab Plain and their past, present, and future states were examined. New scenarios of use increase of 5%, 10%, and 15% higher use were used in GMS10.5. Then, the IMDPA model was employed to assess the rate of desertification of groundwater tables in the plain in the past, present, and future.

The results showed that the highest depletion was -3.16, -12.87, -23.89, and -30.30 in the base years of 2003, 2008, 2013, and 2018, respectively. It has happened due to the digging of deep and semi-deep wells. The highest increase in water level balance over 2003-2035 has been -59.5, -61.3, and -63.2 m under the scenarios of 5%, 10%, and 15% higher use, respectively. Prediction of the qualitative parameters of EC and SAR for 2019, 2024, 2029, and 2035 indicates that these parameters will increase in 2035. The resulting pollution will move from the south towards the north. The weighted mean of quantitative values of the factors influencing water resource degradation shows that desertification occurs in the studied region at different rates. Over time, the desertification rate of water criterion will expand towards the north, south, center, and west of the area. The results for different periods are depicted in a figure. It can be asserted that a great part of the region is in the low desertification class in the base period, but the area of this class decreases. The medium desertification class expands over time. The area of the medium desertification class has been 0, 32.37, 46.35, and 123,48 km2 km2 in 2003, 2008, 2013, and 2018, respectively. The very low desertification class has been 125.93, 6.54, 0.23, and 0.07 during this period. In the 5% higher use scenario, the very low, low, and medium desertification classes have decreased by 2.64, 45.47, and 72.04 km2 over 2009-2035.  The very high desertification class has increased by 120.14 km2 in this scenario. It was the same for the scenarios of 10% and 15% higher use. The very low, low, and medium desertification classes have decreased by 0.06, 72.18, and 48.00 km2 in the 10% higher use scenario and by 47.96, 0.06, and 72.14 km2 in the scenario of 15% higher use over 2019-2035. The very high desertification class has increased by 120.189 and 120.187 km2 in these scenarios, respectively.

The results revealed that desertification is happening across the plain at different rates and will continue at a higher rate in the future. It can be summarized that all components of nature are chained to one another. A change in one component entails a change in the other parts of the system so that a decline in groundwater quantity reduces its quality. So, approaches should be adopted to prevent the further quantitative and qualitative decline of groundwater tables, and mechanisms should be taken to minimize damages to the whole ecosystem. Finally, some executive approaches for preventing land degradation and desertification based on the regional water criterion include reforming cropping patterns, adopting modern irrigation methods, and feeding the bed of the plain by flooding.