Evaluation of temporal-spatial changes of groundwater resources in Kashmar plain based on time series analysis of precipitation and drought data

Groundwater is one of the most important resources of water in the world. Studies show that low rainfall, persistent droughts, and over-exploitation have caused economic and environmental damage. Therefore, this study was conducted to evaluate the effects of rainfall and drought on the groundwater of Kashmar plain as one of the most important fertile plains of Khorasan Razavi in eastern Iran, using Man-Kendall and Petit time series. In this study, from the 30-year statistical period (1989-2017), the rainfall data of Kashmar meteorological station were used to evaluate the effects of meteorological drought, with SPI index. Furthermore, the statistical data of 17 piezometer wells in the study area in 23 years (1996-2017) were used to assess groundwater drought, with PSI index. The results of the time series analysis of the SPI index in different ranges of 3, 6, 12, and 24 months in 1989-2017 showed that the gradual changes in the range of 6 and 12 months at the five percent significant level (p-value = 0.05), which the point of change was 1999-2000, however, it was not significant in 3 and 24 months. Since p-value≠ 0.05, the time series of the PSI index in Kalat-e-Rahim and Khalilabad wells (in the southern and northern parts of the region) is not significant, but the other wells are significant. This means that Kalat-e-Rahim and Khalilabad wells were in better condition during droughts due to aquifer operations in the area. Therefore, Kashmar plain has suffered from groundwater drought from 1996 to 2018. According to the SPI and PSI indices, meteorological drought has affected groundwater resources, but a more important factor in groundwater drought is the over-exploitation of groundwater, which has led to declining 40 cm groundwater levels per year in Kashmir plain.