Public Release: 

A basis for the application of drought indices in China

Science China Press

How to choose an appropriate drought index in drought monitoring, forecasting and research is one of difficulties. Different drought indices could present dissimilar abilities when applied in various regions, because of the different aspects and physics of drought they address, which, of course, raises the problem of regional applicability. A recent study has identified the regional applicability in China of seven drought indices: the Palmer Drought Severity Index (PDSI), modified PDSI (PDSI_CN) based on observations in China, self-calibrating PDSI (scPDSI), Surface Wetness Index (SWI), Standardized Precipitation Index (SPI), Standardized Precipitation Evapotranspiration Index (SPEI), and soil moisture simulations conducted using the community land model driven by observed atmospheric forcing (CLM3.5/ObsFC).

The study titled "Regional applicability of seven meteorological drought indices in China", which was published in Science China Earth Sciences, was done by Dr. Yang Qing et al. in Institute of Atmospheric Physics Chinese Academy of Sciences, and its corresponding author is Prof. Ma Zhuguo. Using terrestrial water storage obtained from the Gravity Recovery And Climate Experiment (GRACE), the observed soil moisture and streamflow, the regional applicability of seven drought indices and their ability to represent the long-term trend of dry/wet variations in China have been evaluated systematically.

Previous studies on the regional applicability of drought indices have focused mostly on the global or regions with abundant observations of terrestrial hydrological variations. In addition, variables used to identify the performance of drought indices tend to be precipitation, soil moisture and runoff. In the study, besides those traditional test variables, terrestrial water storage is used to evaluate the regional applicability of drought indices in China. It could provide a more reasonable evaluation of drought indices.

Results showed that the PDSI, PDSI_CN, and scPDSI perform consistently well in drought monitoring in China with respect to the other drought indices, and the performance of the scPDSI is the best. However, the value range of the scPDSI is reduced slightly and therefore, its wet/dry classification should be adjusted. For the PDSI and PDSI_CN, there might be some problems in arid and humid areas because of unsuitable empirical parameters. The SPI and SPEI are both appropriate in humid areas but not in arid and semiarid areas. This is because the ratio of evapotranspiration anomaly (caused by temperature variation) in the surface water balance is relatively large in arid and semiarid regions with respect to humid regions. The SPI neglects the contribution of the temperature anomaly and thus, it tends to induce wetter result in arid and semiarid areas and drier results in humid areas. The SPEI is sensitive to the calculation schemas of potential evapotranspiration. The contribution of the temperature anomaly to drought tends to be overestimated by the SPEI in arid and semiarid areas and consequently, a drier result is obtained when the Thornthwaite method is used to estimate potential evapotranspiration. The CLM3.5/ObsFC is reasonable before 2000 but not after 2000, especially in arid and semiarid areas, and their reason requires further investigation. The SWI presents similar characteristics of dry/wet variation to the other indices on interannual and decadal timescales.

These findings could deepen our understanding to the application of drought indices in China, which will provide a basis for how to choose an appropriate drought index for a given drought research in different regions.

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This research was funded by the National Basic Research Program of China (2012CB956201), the National Natural Science Foundation of China (41275085; 41530532; 41305062), the National Key Technology R&D Program of China (2013BAC10B02) and China Special Fund for Meteorological Research in the Public Interest (GYHY201506001-1).

See the article: Yang Q, Li M X, Zheng Z Y, Ma Z G. 2017. Regional applicability of seven meteorological drought indices in China. Science China Earth Sciences, doi:10.1007/s11430-016-5133-5

This article was published online (http://engine.scichina.com/publisher/scp/journal/SCES/doi/10.1007/s11430-016-5133-5?slug=full%20text), in the Science China Earth Sciences.

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