Spatiotemporal variations of groundwater drought indices, Case study: Zohreh- Jarrahi watershed

Considering the importance of groundwater resources in the country, the study of hydrogeological droughts and effective factors on groundwater drawdown is essential to provide management solutions of these vital resources. Therefore, the purpose of this study is to analyze the trend of groundwater variations and assessment of groundwater drought in the Zohreh- Jarrahi watershed using SDI and GRI drought indices in a ten-year statistical period (2006-2016). The results show that in most study areas, there is a correlation between GRI and SDI indices. However, in some cases, the effect of hydrological drought on groundwater was shown with the delay of 6 months to one year. In general, the GRI drought index is more prominent during the ten-year statistical period in the center and around the west of the Zohreh- Jarrahi watershed and in particular the Imamzadeh Jafar study area. Moreover, in the final years of statistical period, the study areas in the southeastern part of the region have also been affected by droughts which are also correlated with SDI values. In the year 2015- 2016, the groundwater of the Leishter study area, according to the GRI index, has a severe drought with a value of 1.60, and according to this indicator, the average drought in the same year with a value of 1.42 in the Fahlian study area occurred. Although, in most cases, the occurrence of climate drought and consequently hydrological droughts caused a groundwater drawdown in the watershed area, but the results of the comparison between the two types of drought indicate that other factors such as excessive groundwater withdrawal are also effective.