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Open AccessArticle

A Counting Process Approach for Trend Assessment of Drought Condition

National Research Council, Institute for Bioeconomy, 50019 Sesto Fiorentino, Italy
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Hydrology 2019, 6(4), 84; https://doi.org/10.3390/hydrology6040084
Received: 30 June 2019 / Revised: 24 September 2019 / Accepted: 25 September 2019 / Published: 27 September 2019
This paper discusses some methodological aspects of the historical analysis of drought, particularly the trend assessment. The Standardized Evapotranspiration Index (SPEI) is widely used as a measure of drought condition. Since different SPEI thresholds allow classifying the risk into moderate, severe, and extreme, the drought occurrence becomes a counting process. In this framework, would a statistical trend test based on a Non-Homogeneous Poisson Process (NHPP) give a similar result of the nonparametric Mann–Kendall (M-K) test? In this paper, we demonstrate that the NHPP approach is able to characterize the information given by the classical M-K approach in term of drought risk classes. Furthermore, we show how it can be used to reinforce the framework of drought trend analysis in combination with a standard non-parametric approach. At a global scale, we find that: (1) areas under increasing risk of drought identified by the NHPP approach are considerably larger in comparison to those identified by M-K; and (2) the results of the two tests are different during crucial periods such as hydrological droughts in winter and spring. View Full-Text
Keywords: Mann–Kendall test; Non-Homogeneous Poisson Process; Standardized Evapotranspiration Index (SPEI); statistical hydrology Mann–Kendall test; Non-Homogeneous Poisson Process; Standardized Evapotranspiration Index (SPEI); statistical hydrology
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Di Giuseppe, E.; Pasqui, M.; Magno, R.; Quaresima, S. A Counting Process Approach for Trend Assessment of Drought Condition. Hydrology 2019, 6, 84.

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