Spatio-Temporal Analysis of Droughts in Semi-Arid Regions by Using Meteorological Drought Indices

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

Understanding Hydrological Repartitioning and Shifts in Drought Regimes in Central and South-West Asia Using MODIS Derived Perpendicular Dought Index and TRMM Data

In this paper, we use perpendicular drought indices (PDIs) and precipitation patterns to identify hydrological repartitioning in agricultural regions located in central and south-west Asia over the last decade. The spatio-temporal patterns of surface drought derived from perpendicular drought index (PDI) and modified perpendicular drought index (MPDI) from 250-mMODerate Resolution Imaging Spectroradiometer (MODIS) data in 8-day time steps are compared against two other drought indices: the Standardized Precipitation Index (SPI) as a meteorological drought index and the potential evapotranspiration (ET ) as an agro-meteorological drought index, along with 8-day MODIS Normalized Difference Vegetation Index (NDVI). The coefficient of variation as the ratio of standard deviation over inter-annual mean drought indices, precipitation from Tropical Rainfall Measuring Mission (TRMM) data are employed to analyse trends and shifts of hydrological regimes and its connection to both climate change and anthropogenic activities in the study area. Significant correlations are found between the PDI, the MPDI and precipitation and other applied meteorological and agro-meteorological drought indices. The results show that Central Asia is one of the areas across the globe experiencing dramatic shifts in hydrological regimes, and is being severely impacted by population growth and climate change. While acknowledging previous studies that used the PDI and the MPDI over some study regions in Iran, this paper, however, confirms implementation of higher resolution data (MOD09Q1) in both spatial (250 m) and temporal (8-days) dimensions shows a greater agreement between the drought information extracted by the PDI, MPDI, and field meteorological measurements. Supported by satellite based precipitation observations, we conclude that the perpendicular drought indices can be used as a drought early warning system over arid and semi-arid climatological conditions

A Re‐examination of Perpendicular Drought Indices over Central and South‐West Asia

Drought monitoring models and products assist decision makers in drought planning, preparation, and mitigation, all of which can play a role in reducing drought impacts. In this study, the performance of two newly developed remote sensing-based drought indices, the perpendicular drought index (PDI) and modified perpendicular drought index (MPDI), are further explored for regional drought monitoring in agricultural regions located in central and south western Asia. The study area covers regions from moderate and wet climatological zones with dense vegetation coverage to semi-arid and arid climatological conditions with moderate to poor vegetation coverage. The spatio-temporal patterns of surface drought derived by PDI and MPDI from 250m MODerate Resolution Imaging Spectroradiometer (MODIS) data in 8-day time steps are compared against two other drought indices: the Standardized Precipitation Index (SPI) as a meteorological drought index and the potential evapotranspiration (ET0) as an agro-meteorological drought index, which both were calculated based on field-measured precipitation and regional meteorological parameters. In addition, 8-day MODIS Normalized Difference Vegetation Index (NDVI) was calculated and its performance to detect drought occurrence and measuring of drought severity compared with the two perpendicular drought indices. Significant correlations were found between the PDI, the MPDI and precipitation and other applied meteorological and agrometeorological drought indices. The results confirm previous studies which has been analyzing the PDI and the MPDI over some study points in Iran. In this research, however, implementation of higher resolution data (MOD09Q1) in both spatial (250 m) and temporal (8-days) dimensions revealed a greater agreement between the drought information extracted by the MPDI, PDI and field meteorological measurements. It could be concluded that the applied perpendicular indices could be used as a drought early warning system over case study region and other regions with similar arid and semi-arid climatological conditions