Abstract
Six meteorological drought indices including percent of normal (PN), standardized precipitation index (SPI), China-Z index (CZI), modified CZI (MCZI), Z-Score (Z), the aridity index of E. de Martonne (I) are compared and evaluated for assessing spatio-temporal dynamics of droughts in six climatic regions in Iran. Results indicated that by consideration of the advantages and disadvantages of the mentioned drought predictors in Iran, the Z-Score, CZI and MCZI could be used as a good meteorological drought predictor. Depending on the month, the length of drought and climatic conditions of the region, they are an alternative to the SPI that has limitations both because of only a few available long term data series in Iran and its complex structure.
Highlights
Drought is a natural local or regional phenomenon, its basic cause being the lack of precipitation over a time period
Linear regressions between the monthly values of the standardized precipitation index (SPI) and Z-Score, China-Z index (CZI), modified CZI (MCZI), percent of normal (PN) and I from 1950 to 2005 indicate that the SPI and Z-Score, CZI, MCZI, PN and I, respectively, in general show a good relationship for the time scale of one month
The linear regressions between the seasonal values of the SPI and Z, CZI, MCZI, PN and I from 1950 to 2005 indicate that the SPI and Z, CZI, MCZI, PN and I in general show a good relationship for the time scales of three-months, but less significant than for the one-month time scale and depending on the season and climatic region (Table 4)
Summary
Drought is a natural local or regional phenomenon, its basic cause being the lack of precipitation over a time period. The Deciles Index [4], which is operational in Australia, the China-Z index (CZI), which is used by the National Metrological Center of China [5] and the standardized precipitation index (SPI) [6], which has gained world popularity Most of these indices are calculated using climate data (rainfall, or temperature). Based on an analysis of the drought in the Southern Plains and the southwestern United States in the spring of 1996, the SPI has been shown to be a more reliable index of developing drought conditions than the PDSI [8] This conclusion is based on the responsiveness of the SPI to emerging precipitation deficits at shorter time scales (e.g., three months). The SPI is simpler than the PDSI in calculation and is more spatially consistent and it can be used, in risk and decision analyses [10].The choice of indices for drought monitoring in a specific area should eventually be based on the quantity of climate data available and on the ability of the index to consistently detect spatial and temporal variations during a drought event [11]
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