ABSTRACT
In order to adopt appropriate measures to fight the effects of drought, drought monitoring systems are one of the most important tools that provide updated information of droughts’ durability, severity and geographical development in a an area. Meteorological drought can be defined as an emergence signal of other various droughts. A large body of research has been done regarding the drought monitoring using meteorological drought index. (Hong et al., 2001; Kim et al., 2009; Naserzadeh et al., 2013). Much research has been done in the field of drought monitoring by using the hydrological indicators such as flow, storage reservoirs. Drought planning on the basis of reservoir volume was examined in a study by Westphal et al., (2007). Using reservoir modeling with a daily scale in system of water resources in West Springfield Massachusetts, they calculated the probability of failure of the reservoir which is the same as reaching a critical size of volumes. In this method, alert levels of drought are classified in four levels of normal, mild, moderate, and severe categories in which there is a range of possibilities of the system failure. In a study by Yang et al., (2012), combined reservoir index for the Tsengwen reservoir was made including three indicators of Drought Risk Index (DRI), Sustainability Index (SUI), and Modified Sustainability Index (MSUI) for the area selected in order to determine MSUI’s threshold for different levels of drought stress of standard classification of drought provided by the water resources Agency of Taiwan based on the rate of reduction of water use for public and agriculture.Using this indicator, they classified drought. Comparison of meteorological and hydrology indicators has attracted a few researchers’ attention, Morid & Paimozd (2007) are two of them. They compared Chang method with EDI index for daily drought monitoring in Tehran province and it became clear that Chang method has greater sensitivity to drought, especially in the
Index of SPI and EDI by hydrological method based on reservoir monitoring for drought monitoring of ZayandehRud water resources system. Results indicated that the index of SPI6 showed better reaction in early warning of drought, the index of EDI for announcing the end of drought and alignment reservoir method for the in-between periods of drought. As mentioned before, some researches have been carried out in the field of monitoring and warning of drought using reservoir level in Iran and other parts of the world. In this research, first monitoring drought according to reservoir level was carried out by the use of combined reservoir index and Probabilistic approach. In the end, these methods were compared with SPI at time scales 6 and 9 months at announcing different levels of drought.
