Drought indices and indicators revisited
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REVIEW PAPER
Drought indices and indicators revisited Yohannes Yihdego 1,2 & Babak Vaheddoost 3 & Radwan A. Al-Weshah 4 Received: 14 August 2018 / Accepted: 11 January 2019 # Saudi Society for Geosciences 2019
Abstract There are numerous drought indicators used by decision makers all around the globe which have been developed to fulfill specific needs. By far, risks associated with drought and related consequences have become a bold topic for scientists in which debates still taking place everywhere. No global drought indices could provide universally accepted results since almost all of these indices are based on observed data as key performance indicators. In this respect, researchers spend a lot of effort on this issue for a better understanding on the various indices which are proposed until now. It is crucial to get a better sense on how drought can develop and how it can be monitored. It is also important to understand that, recent global challenges like climate change also amplifies the obligation on continues effort toward developing better indicators and methods to monitor droughts. As climate patterns change or a seasonal shift occurs, predefined drought indicators become useless. In this review, the concepts of drought indices and indicators are revisited and evaluated. Pros and cons of frequently used indices are addressed and the major differences between them are bolded. It is concluded that each index is applicable to fulfill expectations of a specific drought type while pre-knowledge about each case is very crucial. However, there is a need to develop a composite drought index to integrate all relevant data and drought definitions, with respect to the dominant types of monthly droughts in time and space together with climate change scenarios. Keywords Drought indices . Climate change . Meteorology . Rainfall failure . Drought risk . Arid region
Introduction Definition of drought Since droughts become more common worldwide, debates on the definition and perspectives of the drought become more tangible and there is no globally accepted standard definition for drought. Even among drought experts, a single definition of drought is hard to agree on. To brief these individuals, a deficit in precipitation from an expected mean within a time frame can be identified as drought (Svoboda et al. 2002; Sheffield and Wood 2012; Eslamian 2014; Yihdego 2016;
Yihdego and Eslamian 2016; Yihdego and Webb 2016; Yihdego et al. 2016, Azmi et al., 2016). Hence, one needs to realize the context in which the drought and its impacts are expressed. Wilhite and Glantz (1985) identified more than 150 realization of drought in the literature; while from those, drought can be classified into four major types: (i) meteorological, as a reduction in precipitation; (ii) agricultural, as a lack of moisture in soil; (iii) hydrological, tracked down considering the decline in stream-flows and runoffs; and finally (iv) socioeconomic droughts in human water use while there is also another definition of drought based on ecological wate
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