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What is difference between CZI (China-Z Index) and MCZI (Modified CZI)?

The China-Z Index (CZI) is a drought index (Ju et al., 1997) that was introduced to the National Meteorological Centre of China (NMCC) in the early 1990s. Unfortunately, the origin of the CZI cannot be easily documented. This index is called the 'China-Z Index'.

The National Climate Center of China developed the CZI in 1995 as an alternative to the SPI (Ju et al., 1997) when mean precipitation follows the Pearson type III distribution. Further details can be found in Wu et al. (2001). Furthermore, the MCZI can also be calculated using the formula above but substituting the median precipitation for mean precipitation.

Salehnia et al (2017) assessed the ability of eight precipitation-based drought indices SPI (Standardized Precipitation Index), PNI (Percent of Normal Index), DI (Deciles index), EDI (Effective drought index), CZI (China-Z index), MCZI (Modified CZI), RAI (Rainfall Anomaly Index), and ZSI (Z-score Index)) calculated from the station-observed precipitation data and the AgMERRA gridded precipitation data to assess historical drought events during the period 1987-2010 for the Kashafrood Basin of Iran. In this paper you can study the performance of CZI and MCZI, beside other meteorological drought indices.

Many drought indices, such as the China-Z index (CZI) (Wu et al., 2001), are widely used while the Standardized Precipitation Index (SPI) (McKee et al., 1993) has achieved world-wide popularity. Wu et al. (2001) expressed three indices, including Standard Precipitation Index (SPI), China Z and Z-Score Index (ZSI) for the dry and humid climate in China and described their advantages and disadvantages by monthly precipitation data. They also attempted deferential deduction of Standard Precipitation Index and Modified CZI. The overall differences between these two indices reduced significantly compared to the difference between the SPI and CZI.

Ref: Ju XS, Yang XW, Chen LJ, Wang YM. 1997. Research on determination of indices and division of regional flood/drought grades in China (in Chinese). Quarterly Journal of Applied Meteorology 8(1): 26-33.

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