Appraising regional multi-category and multi-scalar drought monitoring using standardized moisture anomaly index (SZI): A water-energy balance approach

The uncertainties in atmospheric water demand used in evaluating drought indices are the primary cause of discrepancies between them, especially in water-limited regions. This study evaluated Standardized Moisture Anomaly Index (SZI) using a combined water-energy balance approach, and compared the performance with the Standardized Precipitation Evapotranspiration Index (SPEI) and self-calibrated Palmer Drought Severity Index (ScPDSI) over seven climatic regions in China from 1948 to 2017. The atmospheric water demand in SZI is evaluated using climatically appropriate precipitation for existing conditions (CAFEC), which takes into account most parts of the surface water-energy balance (i.e., precipitation, evapotranspiration, runoff, and soil moisture recharge and loss). The relative performances of SZI, SPEI, and ScPDSI for multicategory and multi-scalar drought identification are reported in terms of Pearson correlation coefficient. Through a series of cross-comparisons, our result explains that the SZI, SPEI, and ScPDSI drought indices presented dissimilar abilities in different regions, which of course, raises the issue of regional applicability. The performance of SZI is better than SPEI and ScPDSI in both humid and non-humid regions. Although the consistency of SPEI is similar to SZI across different temporal scale, it is more appropriate for multi-scalar drought analysis in humid regions. The ScPDSI are inconsistent in identifying multicategory drought. The enhanced drought appraisal with the SZI is the consequence of a more objective evaluation of atmospheric water demand by incorporating precipitation, runoff, and change in water storage, all that control meteorological, hydrological, and agricultural droughts, respectively. The SZI can offer a better multi-category and multi-scalar droughts information, which could aid in providing valuable early warning of rapidly evolving drought most notably in the water-limited region.