Appropriate application of the standardized precipitation index in arid locations and dry seasons

作者：Hong Wu, Mark Svoboda, Michael J. Hayes, Donald A. Wilhite, Fujiang Wen · 发表于：International Journal of Climatology · 年份：2006 · DOI：10.1002/joc.1371 · 被引用次数：426 · 研究领域：Hydrology and Drought Analysis、Climate variability and models、Climate change impacts on agriculture

Abstract The Standardized Precipitation Index (SPI) is now widely used throughout the world in both a research and an operational mode. For arid climates, or those with a distinct dry season where zero values are common, the SPI at short time scales is lower bounded, referring to non‐normally distributed in this study. In these cases, the SPI is always greater than a certain value and fails to indicate a drought occurrence. The nationwide statistics based on our study suggest that the non‐normality rates are closely related to local precipitation climates. In the eastern United States, SPI values at short time scales can be used in drought/flood monitoring and research in any season, while in the western United States, because of its distinct seasonal precipitation distribution, the appropriate usage and interpretation of this index becomes complicated. This would also be the case for all arid climates. From a mathematical point of view, the non‐normally distributed SPI is caused by a high probability of no‐rain cases represented in the mixed distribution that is employed in the SPI construction. From a statistical point of view, the 2‐parameter gamma model used to estimate the precipitation probability density function and the limited sample size in dry areas and times would also reduce the confidence of the SPI values. On the basis of the results identified within this study, we recommend that the SPI user be cautious when applying short‐time‐scale SPIs in arid climatic reg...