What are meteorological drought indices?

In general, drought is a complex phenomenon that has affected more people during the last century than any other natural disaster (Below, 2007). Several methods have been used as drought assessment tools such as measurement of lack of rainfall, reduced levels of streamflow and water storage, and Drought Indices. Drought Indices have been commonly used to quantify drought conditions and to assess drought severity around the world (Keyantash and Dracup, 2002; Salehnia et al., 2017). Investigation on drought characteristics such as severity, duration, and frequency is crucial for water resources planning and management in a river basin (Dodangeh, 2017).

During the last decade, drought monitoring has made great strides with monitoring and early warning systems being established in several countries and regions. Different drought indices have their own advantages and disadvantages and each index may not represent the drought conditions at every location correctly (Vicente-Serrano, 2008). A drought indicator is calculated using data such as precipitation or soil moisture to provide a measure of the moisture conditions at a location. Drought indicators are calculated with respect to normal moisture conditions.

There is no uniform method to characterize drought conditions and there are a variety of drought indices that can be used as tools to monitor meteorological drought (Quiring 2009). The input variables required for the calculation of meteorological drought indices vary depending on the drought index in question, but include precipitation, temperature, available water holding capacity of the soil and others that are representative of the moisture in the system. Some examples of meteorological drought indices are the Palmer Drought Severity Index (PDSI), Palmer Z-Index, the Standardized Precipitation Index (SPI), the Standardized Precipitation and Evapotranspiration Index (SPEI), the Effective Drought Index, and deciles.

Because of the complex definition of droughts, and the lack of soil moisture observations, several indices have been developed to characterize (meteorological, soil moisture, and hydrological) drought (see, e.g., Heim Jr., 2002; Dai, 2011). Some meteorological drought indices are based solely on precipitation data, these include:

SPI (Standardized Precipitation Index), DI (deciles index), PN (Percent of Normal Index), RAI (Rainfall Anomaly Index), EDI (effective drought index), CZI (China-Z index), MCZI (modified CZI), ZSI (Z-Score Index). Agrimetsoft team has developed two tools for calculating rain-based meteorological drought indices, namely RDIT (Rain-based Drought Indices Tool) software, and MDM (Meteorological Drought Monitor) software application.

The MDM tool calculates SPI (Standardized Precipitation Index), DI (deciles index), PN (Percent of Normal Index), RAI (Rainfall Anomaly Index), EDI (effective drought index), CZI (China-Z index), MCZI (modified CZI), and ZSI (Z-Score Index).

The RDIT tool can calculate and perform rain-based drought indices. This software can calculate eight indices of meteorological drought. Input and output data are in excel format file. For input data, RDIT (Rain-based Drought Indices Tool) is a smart. It can assess your data and check blank cells and produce data for ‘null’ cells. This software calculates the same indices as MDM tool, but it can also calculate severity and duration of drought event, easily. These indices are normally calculated on monthly time scales of 1, 3, 6, 9, 12 and 24. Short term indices, for time scales of 3 and 6 months, are generally used to classify meteorological and agricultural droughts; and long-term indices, for time scales above than 6 months are normally used to classify hydrological and socio-economic droughts (Karavitis, Alexandris, Tsesmelis, & Athanasopoulos, 2011).

There are other indices in meteorological drought type that they need other meteorology, climatology, or other inputs beside precipitation, as follows:

• PDSI (Palmer Drought Severity Index), Palmer (1965).
• PHDI (Palmer Hydrological Drought Index), Palmer (1965).
• SPEI (Standardized Precipitation Evapotranspiration Index), Vicente-Serrano et al., 2010.
• RDI (Reconnaissance Drought Index), Tsakiris and Vangelis, 2005.
• KBDI (Keetch-Byram Drought Index), Keetch and Byram (1968).

Agrimetsoft has developed a comprehensive tool for calculating different meteorological drought indices with name of DMAP (Drought Monitor And Prediction) software tool. In DMAP the input file can be in diffe