In this paper, drought was evaluated for the Mosul Dam Watershed, Iraq, which is considered one of the most important dams in Iraq. The evaluation of drought was studied using two types of meteorological drought indices, namely Reconnaissance Drought Index (RDI) and Standardized Precipitation Index (SPI), and Hydrological drought index which is Streamflow Drought Index (SDI). Monthly precipitation and air temperature for the period 1979-2013 downloaded from Climate Forecast System Reanalysis (CFSR) were used as weather input data for the RDI and SPI. Streamflow obtained from the gauge station in the study area were used as input data for the SDI. The indices computed by the DrinC software for a 12-month time scale. The results were analysed and the Drought Frequency Patterns (DFPs) were computed for each index. The results showed that potential evapotranspiration plays a major role in causing drought, in addition to precipitation. The RDI gave more dry periods than the other two indices, as it depends on precipitation and potential evapotranspiration. Likewise, all indices are identical in that the period is divided into two parts: the first part, which extends from the beginning of the period 1979 to the end of the nineties 1990s, is considered wet and the second part, which extends to the end of the period 2013, is drier. The Hydrological Drought Index SDI gives a drought of greater severity (Moderate drought for the years 2002, 2003 and 2004) compared to the other two indices.

Drought is one of the most significant natural disasters in Iraq. It has a strong impact on the water resources in Iraq. Consequently, it causes massive environmental damage, economic deficiency, and social problems to the country. Therefore, more considerations towards the study and management of drought has become of vital importance in recent decades. In this paper, three drought indices (DIs) were computed for evaluation of the spatiotemporal of drought within Derbendikhan Dam Watershed (DDW) in the Diyala River Basin, Iraq. Based on the monthly weather data for the period (1984 – 2013) downloaded from the Climate Forecast System Reanalysis (CFSR) for eight stations located within DDW. The Reconnaissance Drought Index (RDI), standardized precipitation index (SPI) and Streamflow Drought Index (SDI) at 12-month time scale were computed to assess droughts in the DDW. For each index, the temporal variations of the drought severity and Drought Frequency Patterns (DFPs) for the period (1984 – 2013) were computed and analyzed. In addition, spatial distributions of the drought severity for each index were mapped and investigated. Accordingly, the DFPs were compared to specify the dominant and/or more frequent DFPs. The results show that the performances of different DIs are strongly correlated with the dominant factors of droughts and drought duration. Also, the SPI and SDI are less accurate than the RDI when both precipitation and evaporation are the main factors controlling the drought events. However, the SPI and SDI indices are identical in the same proportions of the dry years which are less than the ratio of dry years to an RDI, but the severity of the drought from the SDI results is higher than the severity of the drought relative to the SPIand RDI. The three indices indicate that the Eastern region is drier than the Western region, which is somewhat wet.