Multiscale evaluation of the Standardized Precipitation Index as a groundwater drought indicator

Rohini Kumar*, Jude L. Musuuza, Anne F. Van Loon, Ryan Teuling, Roland Barthel, Jurriaan Ten Broek, Juliane Mai, Luis Samaniego, Sabine Attinger

*Corresponding author for this work

Research output: Contribution to journalArticleAcademicpeer-review

69 Citations (Scopus)


The lack of comprehensive groundwater observations at regional and global scales has promoted the use of alternative proxies and indices to quantify and predict groundwater droughts. Among them, the Standardized Precipitation Index (SPI) is commonly used to characterize droughts in different compartments of the hydro-meteorological system. In this study, we explore the suitability of the SPI to characterize local- and regional-scale groundwater droughts using observations at more than 2000 groundwater wells in geologically different areas in Germany and the Netherlands. A multiscale evaluation of the SPI is performed using the station data and their corresponding 0.5° gridded estimates to analyze the local and regional behavior of groundwater droughts, respectively. The standardized anomalies in the groundwater heads (SGI) were correlated against SPIs obtained using different accumulation periods. The accumulation periods to achieve maximum correlation exhibited high spatial variability (ranges 3-36 months) at both scales, leading to the conclusion that an a priori selection of the accumulation period (for computing the SPI) would result in inadequate characterization of groundwater droughts. The application of the uniform accumulation periods over the entire domain significantly reduced the correlation between the SPI and SGI (∼ 21-66%), indicating the limited applicability of the SPI as a proxy for groundwater droughts even at long accumulation times. Furthermore, the low scores of the hit rate (0.3-0.6) and a high false alarm ratio (0.4-0.7) at the majority of the wells and grid cells demonstrated the low reliability of groundwater drought predictions using the SPI. The findings of this study highlight the pitfalls of using the SPI as a groundwater drought indicator at both local and regional scales, and stress the need for more groundwater observations and accounting for regional hydrogeological characteristics in groundwater drought monitoring.

Original languageEnglish
Pages (from-to)1117-1131
JournalHydrology and Earth System Sciences
Issue number3
Publication statusPublished - 2016

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