Analysis and Investigation of Hydrological Drought Indicators in Mahenshan of Zanjan Province

Drought, as one of the natural disasters, has significant impacts on the environment. Although its occurrence is inevitable, its negative effects can be mitigated by taking measures. Freshwater groundwater, due to its sustainability and high quality, plays an important role in providing drinking water and socio-economic development, especially in dry and semi-arid regions. In this study, drought in Mahneshan County was investigated using various indices. 30 years of rainfall data from Mahneshan station were analyzed. To investigate climatic drought, the SPI index was used, to determine wet and dry periods, the 5 and 7 year moving averages of annual rainfall were used, and to investigate hydrological drought, well data and the GRI index were used. The findings show that climatic and hydrological droughts have occurred in the Mahneshan region and that there is a significant correlation between the SPI index and groundwater level changes. According to the findings, drought is one of the main challenges in the Mahneshan region. The use of various indices to investigate drought is necessary and its negative effects can be mitigated with proper planning. This study only focuses on a specific region and other factors affecting drought and ways to reduce its effects are not investigated. The aim of this study is to provide an overview of the drought situation in the Mahneshan region and the need to pay attention to this phenomenon in future planning and actions.

This study is of an applied nature with a descriptive-analytical approach. To collect data, two methods were used: library studies and field surveys. In the field section, various methods were used, such as questionnaires, interviews, and observations, to collect the opinions and views of the local residents, expert information from specialists, and field surveys of water resources and water transmission systems. To complete the information, inquiries were made from relevant organizations such as the Rural Affairs Deputy and the Rural Water and Sewerage Administration. Also, by visiting the region in the field, information related to water resources, water allocation, and other drought-related matters were collected and analyzed and interpreted using scientific methods. To investigate climatic drought in the region, the Standard Precipitation Index (SPI) was used. This index is calculated using long-term rainfall data (30 years) and can show wet, dry, and normal periods in the region. In addition to the SPI index, the 5 and 7 year moving averages of annual rainfall were also used to determine wet and dry periods. In this method, the average rainfall in a specific period of time (5 or 7 years) is calculated and compared with the long-term average rainfall. To investigate hydrological drought in the region, data from wells with appropriate distribution and long-term data were used. Changes in groundwater level in these wells were calculated by the Groundwater Recharge Index (GRI). The GRI indicates the amount of water entering the groundwater and can be used to assess the status of groundwater resources in the region.

Analysis of SPI values at different time scales and 5 and 7 year moving averages of rainfall indicates a significant decrease in rainfall in the Mahneshan region over the past 20 years. This downward trend raises concerns about its negative consequences for water resources, agriculture and other water-dependent sectors in the region.Analysis of the GRI index on monthly and annual time scales indicates a decline in groundwater levels in the Mahneshan region. This decline has been exacerbated due to the imbalance between recharge and withdrawal from the groundwater table, especially in recent years with consecutive droughts.Overexploitation of groundwater resources has threatened the sustainability of these resources.Correlation analysis between the SPI and GRI indices indicates a significant correlation between meteorological and hydrological droughts in the Mahneshan region. This correlation is stronger at longer time scales. The findings show that meteorologicaldroughts can lead to hydrological droughts in the region.Analysis of the relationship between meteorological and hydrological droughts with time lags of one, two and three years shows that there is a significant correlation between these two types of droughts with lags of one and two years. This correlation shows that meteorological droughts with lags of one and two years lead to hydrological droughts in the Mahneshan region.

The Mahneshan region has faced a decline in groundwater levels and frequent and severe droughts over the past two decades. Studies show that:The average annual decline in groundwater level has varied over the years. This is due to the diversity in formation type, permeability, hydraulic gradient, and the amount of groundwater withdrawal in different regions. In the 20-year period (1375 to 1395), the groundwater level in the Mahneshan region has dropped by an average of 45 cm annually. This indicates the excessive and unsustainable withdrawal of groundwater resources. Repeated droughts have also exacerbated the trend of groundwater decline. In addition to rainfall, other factors such as overexploitation of groundwater resources also affect groundwater decline. A comparison of the SPI (climatic drought) and GRI (groundwater resources) indices shows that there is a significant relationship between these two indices on monthly and annual time scales. This relationship shows that climatic drought, with a 2-year lag, affects groundwater decline in the Mahneshan region. The lag time between climatic drought and groundwater decline can vary in different parts of the basin, depending on the diversity of formation type and geological characteristics and different groundwater withdrawals.Overall, the results of this study show that the Mahneshan region faces a serious challenge of water scarcity and drought. Overexploitation of groundwater resources and repeated droughts have exacerbated this challenge.