Preprints
https://doi.org/10.5194/hess-2016-467
https://doi.org/10.5194/hess-2016-467
08 Sep 2016
 | 08 Sep 2016
Status: this discussion paper is a preprint. It has been under review for the journal Hydrology and Earth System Sciences (HESS). The manuscript was not accepted for further review after discussion.

Reliability of meteorological drought indices for predicting soil moisture droughts

Devanmini Halwatura, Neil McIntyre, Alex M. Lechner, and Sven Arnold

Abstract. Meteorological drought indices based on precipitation and/or evaporation are commonly used to detect the presence, severity and duration of soil moisture droughts. However, it is debatable whether droughts can be adequately characterised using only precipitation and/evaporation, or whether more physical based methods using soil water deficits and pressures is necessary. To address this question, the performances of two commonly used meteorological drought indices, the Standard Precipitation Index (SPI) and the Reconnaissance Drought Index (RDI), are evaluated against soil moisture droughts identified using a physically based soil water model. Our analysis is based on three sites in Eastern Australia, each representing specific soil-climate conditions. Drought duration and severity were estimated using SPI and RDI and soil water pressure data were simulated with Hydrus-1D. The performance of the two drought indices was measured in terms of their correlation with simulated monthly minimum soil water pressures, and their ability to estimate the frequency with which the simulated pressure drops below threshold values. There was a significant correlation between the two drought indices (SPI and RDI) and the monthly minimum soil water pressure. Failure rate (FR) and false alarm rate (FAR) of drought indices detect soil moisture drought reasonably well (FR and FAR is <50 %) for both drought indices (SPI and RDI) and soil depths (5 cm and 30 cm) (except Melbourne). Overall SPI performs better (except shallow soils in Bourke) than RDI. However an uncertainty of the FR and FAR in the soil water retention curve is always higher than the uncertainties of drought indices. The complexity and the uncertainty in the model encourage to use the simple drought indices, however the model provide physically relevant soil water pressure values which are species specific for plants.

Publisher's note: Copernicus Publications remains neutral with regard to jurisdictional claims made in the text, published maps, institutional affiliations, or any other geographical representation in this preprint. The responsibility to include appropriate place names lies with the authors.
Devanmini Halwatura, Neil McIntyre, Alex M. Lechner, and Sven Arnold
 
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Status: closed
AC: Author comment | RC: Referee comment | SC: Short comment | EC: Editor comment
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Status: closed
Status: closed
AC: Author comment | RC: Referee comment | SC: Short comment | EC: Editor comment
Printer-friendly Version - Printer-friendly version Supplement - Supplement
Devanmini Halwatura, Neil McIntyre, Alex M. Lechner, and Sven Arnold
Devanmini Halwatura, Neil McIntyre, Alex M. Lechner, and Sven Arnold

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Short summary
Droughts indices that only use rainfall/evaporation may not reliably detect soil moisture droughts. Few comparative studies have been published to guide the decision on the most appropriate method for describe soil moisture droughts. We evaluate the performance of drought indices in predicting soil moisture droughts by comparing drought indices with soil water pressure. The failure and false alarm rates of drought indices showed, indices performed reasonably well in detecting soil moist drought.