International Journal of Enhanced Research in Science, Technology & Engineering ISSN: 2319-7463, Vol. 12 Issue 6, June-2023, Impact Factor: 7.957 Page | 136 Assessment of drought using SPI and SPEI methods- A state-of-art review Khyati Mistry 1 , Grishma Salvi 2 , Maulik Kakadiya 3 1,2,3 Assistant Professor, Civil Engineering Department, Chhotubhai Gopalbhai Patel Institute of Technology, Gujarat, India ABSTRACT Drought is a recurrent feature of a nature causing significant damage to the mankind and environment. Due to immense increase in global warming, intensity and frequency of drought has been rising continuously over past decades and became a global issue to research on. There are several indices available to assess the severity of drought, however standardized precipitation index and standardized precipitation evapotranspiration methods are widely used by researchers to determine various characteristics of drought over different geographical area. The present study provides comprehensive review of effectivity of SPI and SPEI methods in evaluating drought along with its benefits and drawbacks. Also, recent work done using these two methods are also mentioned. However, drought is depended on numerous factors that could impact on universal use of SPI and SPEI methods giving possibility of using other methods for drought assessment. Apart from this, a prediction model can also be generated to reduce after effects of drought. Keywords: Drought Assessment, Drought Indices, Drought prediction, spatial changes, SPI, SPEI INTRODUCTION Drought is considered as one of the most disastrous as it inflicts untold numerous miseries on the human communities (Shewale & Kumar, 2005). Due to severity of drought, it attracted the attention of environmentalists, ecologists, hydrologists, meteorologists, geologists and agricultural scientists globally (Swain, Mishra, & Pandey, 2021; Mishra & Singh, 2010). Droughts occur in virtually all climatic zones, such as high as well as low rainfall areas and are mostly related to the reduction in the amount of precipitation received over an extended period of time, such as a season or a year (Mishra & Singh, 2010). Temperatures; high winds; low relative humidity; timing and characteristics of rains, including distribution of rainy days during crop growing seasons, intensity and duration of rain, and onset and termination, play a significant role in the occurrence of droughts (Mishra & Singh, 2010; Wilhite, Svoboda, & Hayes, 2007). Since 2000, the number and duration of droughts has risen 29%. Droughts represent 15% of natural disasters but took the largest human toll, approximately 650,000 deaths from 1970-2019. From 1998 to 2017, droughts caused global economic losses of roughly USD 124 billion. In 2022, more than 2.3 billion people face water stress; almost 160 million children are exposed to severe and prolonged droughts (WMO, 2021). The Indian meteorological department defines drought in any area when the rainfall deficiency in that area is ≥26% of its long term normal. It is further classified in to moderate and severe depending upon whether the deficiency is in between 26 to 50% and more than 50% respectively (IMO, 2020). Drought is basically divided into four categories Meteorological, Hydrological, Agricultural and economic (Wilhite, Svoboda, & Hayes, 2007). The characterization of drought can be done using variety of indices (Handbook of Drought Indicators and Indices, 2017; Nagarajan, 2009). Several drought indices have been derived in recent decades. Basically, a drought index is a prime variable for assessing the effect of a drought and defining different drought parameters, which include intensity, duration, severity and spatial extent (Mishra & Singh, 2010). Methods like Standardised Precipitation Index, Simplified rainfall Index (Swain, Mishra, & Pandey, 2021) Standardised precipitation Evapotranspiration Index (SPEI), Aridity Anomaly Index (AAI), Percent of Normal Precipitation, Weighted Anomaly Standardized Precipitation Index (WASP), Aridity Index (AI), Drought Reconnaissance Index (DRI), Drought Area Index (DAI), Palmer Drought Severity Index (PDSI), Rainfall Anomaly Index (RAI) and many others are available to assess the drought. In the present study, more emphasize is given on utilisation of SPI and SPEI methods for drought characteristics and the reason behind wide usage of it. Also, the possibility of using other indices and prediction model has been suggested by reviewing case studies of drought prone regions. This paper contains a brief introduction of drought as a natural disaster, followed by working methodology, significance of SPI and SPEI methods for worldwide acceptance, recent cases of drought assessment and a conclusion.