Analysis of temporal and spatial relationship between meteorological and hydrological drought in Tehran province

Analysis of temporal and spatial relationship between meteorological and hydrological drought in Tehran province drought is a recurring and temporary natural event which leads to many damages to human life and natural ecosystems. In this study, the Standardized Precipitation Index (SPI) and Stream flow Drought Index (SDI) were used to assess droughts. For this purpose, monthly statistics of 72 rain-gauge stations and 42 hydrometric stations were used in Tehran province and drought indices of SPI and SDI were calculated in the matlab software. In the next stage of their zoning maps of these indices were prepared using ArcGIS software in different periods and the relationship between the two drought indices was obtained using the Pearson correlation coefficient. The results of this study showed that the drought trend has been increased over time in different parts of the province. Also, there was a significant relationship (at confidence level of 99%) between meteorological drought and hydrological drought in the area. The results show that the extent of drought has been increased over time and from north to south of the province. Based on rainfall and discharge data, the occurrence of meteorological drought, either as instantly or with a time delay of one month, has the highest impact on the hydrologic drought. Also, study of the spatial order showed that the highest correlation between meteorological drought and hydrological drought was found in Roudak station because of the small size of its upstream basin compared to position of its rain-gauge and hydrometric stations.