Investigating the relationship between meteorological, hydrological and groundwater resource droughts under the influence of upstream dam reservoir effects

The dam reservoir can change hydrological and groundwater conditions. This affects the drought characteristics downstream of the dams. For studying of these effects, this study used three types of drought indices; Standardized Precipitation Index (SPI), Streamflow Drought Index (SDI) and Groundwater Resource Index (GRI). The results showed that due to the presence of the Marun Dam, water table level of piezometers in downstream of the dam which have higher water table levels is not depended to precipitation (PCP) and flow discharge (Q). However, piezometers farther from the dam had a relatively high correlation with PCP of upstream rainfall stations. This indicates that PCP in the upstream of the dam affects water table level in the downstream of the dam after 4, 6 and 8 months (for 12, 24 and 48-month time scales, respectively). Also, the lag time between GRI and SDI is 1 month. The GRI showed droughts with more severity and duration than SPI and SDI. However, in the downstream of the Marun Dam, GRI showed severe drought before dam construction. Because of increasing water table level after construction of dam, GRI did not show any severe drought in this time. The lag time between SPI and SDI is 1-month. By increasing time scale, the correlation coefficient between different types of droughts and the lag time between SPI and GRI will increase and severity of different types of droughts will reduce. As the distance from the dam increases, the correlation between SPI and GRI increases.