Journal of Watershed Management Research

Extended Abstract
Background: Desertification is a process that causes irreversible changes in the soil and vegetation conditions of a region, leading to an increase in dryness and reduced productivity potential. The destruction of groundwater resources, along with other processes, has been characterized as factors affecting desertification due to the limitations of water resources, reduction of water quality, and excessive exploitation. Subsidence, which is considered the final stage of desertification, will result from the increased use of groundwater resources. Knowing the processes and factors of desertification, as well as their intensity and weakness, is essential for proper management and planning in this context. Ground monitoring is an effective way to monitor desertification. Various models have been presented to evaluate the factors affecting desertification and create related maps for this purpose. Various indicators and criteria can be used by the IMDPA model to efficiently examine the desertification status of each region in the meantime.
Methods: The desert watershed in Daranjir, located in the north of Kerman Province and the south of Yazd Province, includes 12 study areas. The elevation ranges from 925 m in the Daranjir desert to 4465 m in the Kuh Hezar Mountain. The watershed covers an area of about 22,406 km², while the deserts, salt marshes, plains, and foothills cover an area of 28,102 km². The Daranjir desert, which measures 1000 km², is deemed to be the end of the basin's surface and underground water drainage network. Groundwater data was utilized initially to investigate and study soil degradation and land subsidence caused by underground water resources in the studied area. In this way, water quality parameters, such as electrical conductivity, sodium absorption ratio, and total dissolved solids, as well as water quantitative parameters and subsidence rate, were collected in the water year 2002-2018 by referring to the relevant organizations, such as the Iranian Water Resources Research Organization (Tamab), the regional water organization of Yazd and Kerman provinces, as well as previous research. The IMDPA model assessed the desertification situation in the Daranjir desert watershed using two criteria, groundwater and subsidence. To investigate the effect of subsidence and groundwater criteria on desertification intensity in the region, first, the effect of two subsidence and groundwater criteria, and then, by removing the subsidence criterion, desertification intensity was evaluated only based on the groundwater criterion. Geographic information systems and interpolation methods were utilized to zoning indicators and criteria.
Results: According to the electrical conductivity parameter zoning map, nearly 50% of the basin has a high salinity level (more than 5000 microsiemens percent), indicating a very severe level of desertification based on this index. Meanwhile, the zoning map of the sodium absorption ratio parameter showed that more than 50% of the basin's water resources have a low sodium absorption ratio (less than 18), which indicates low expression intensity according to this index. According to this index, desertification intensity is indicated by the drop of over 50 cm in more than half of the basin observed during the investigation of the groundwater level drop. The desertification situation was evaluated with the IMDPA model groundwater criterion, indicating that over 50% of the basin surface had moderate intensity, and almost 20% had a severe status. Desertification intensity was highest in the ranges of Bahadran and Qoriya al-Arab, while it was lowest in the ranges of Qoriya al-Arab. Based on a subsidence map evaluation of three study areas (Kerman-Baghin, Rafsanjan, and Zarand), the Kerman-Baghin area exhibits the highest subsidence rate between 12 and under 7 cm.y. The evaluation of the desertification situation based on two criteria, subsidence and groundwater, in the three areas with subsidence showed that the Rafsanjan area had the highest intensity of desertification, according to the two criteria.
Conclusion: In general, the results showed that the most important factor affecting desertification intensity was groundwater salinity, followed by a drop in the water level, according to the two criteria, groundwater and subsidence. Examining the areas with subsidence and the groundwater level drop in the study areas shows that subsidence has occurred in the areas with a drop in the groundwater level in most cases. The assessment of desertification intensity according to the three water criteria of the IMDPA model shows that desertification in the region is low to very intense, so that the middle class is included at the highest level in the watershed. Based on the percentage of the area of desertification intensity classes, after moderate intensity, areas with extreme intensity, low intensity, and very intense, respectively, are the highest level. The evaluation of the desertification situation by the study area shows that there are areas with a very severe state of desertification at a higher level in the Bahadran area than in the other study areas. This is despite the fact that desertification only has two classes, low and moderate, in the study areas of Saghand, Bardsir, and Qoriya al-Arab. The state of desertification based on the two criteria of "groundwater" and "subsidence" in the three study areas with subsidence maps shows that desertification in the Rafsanjan area is more intense than in the two areas of Zarand and Kerman-Baghin. To control desertification, it is recommended to implement water resource management, including monitoring groundwater extraction and utilizing optimal irrigation methods. Additionally, continuous monitoring and assessment of the desertification status using the IMDPA model and oversight of water quality are essential. Developing vegetation through planting drought-resistant plants and implementing desertification projects will also be effective. Finally, raising awareness among farmers and the local community about sustainable agricultural practices is of great importance.