Reza Hassanzadeh - Department of Civil engineering, Ayatollah Ozma Borujerdi University. Borujerd, Iran.
Mehdi Komasi - Assistant Professor, Hydraulic Structure, Department of Civil Engineering, Faculty of Engineering, University of Ayatollah ozma Borujerdi, Borujerd, Iran.
Amirmohammad Hassanzadeh - Department of civil engineering, Imam Hossein University, Tehran, Iran.
Alireza Derikvand - Department of Civil engineering, Ayatollah Ozma Borujerdi University. Borujerd, Iran.

Today, monitoring groundwater quality and the trend of its changes for drinking, industrial and agricultural uses is very important for the general health of society. Due to changes in groundwater quality that can be due to climatic or human factors, it is necessary to consider and study these resources to maintain their quality. The purpose of this study is to investigate the quality and effective factors in groundwater quality changes in Khorramabad from ۲۰۰۵ to ۲۰۱۸ using the global water quality index (WQI) and coherence and cross wavelet. To achieve this goal, first, the drought assessment of Khorramabad city has been studied according to precipitation data using the index (SPI). Then, using the world water quality index (WQI), the groundwater quality of Khorramabad has been studied. The results showed that the quality of groundwater in Khorramabad during the years ۲۰۰۵ to ۲۰۱۸ was in standard condition. Also, the correlation between the chemical parameters of groundwater has been evaluated. The results of coherence and cross wavelet showed that the relative effect of precipitation with a wavelet coherence coefficient of ۰.۵ had been more compared to other factors in changes in groundwater quality in Khorramabad city. Therefore, it can be said that the relative impact of climatic factors on changes in groundwater quality in Khorramabad has been more than the other factors. Accordingly, appropriate management strategies for groundwater quality resources and mitigation solutions are imperatively needed to ensure the sustainability of the groundwater resource and the protection of public health in Khorramabad city.

SPI, Water Quality, Khorramabad, WQI, Coherence Wavelet