Comparison of Standardized Drought Indices to Monitor the Rapid Onset of Agricultural Drought At a Non-Irrigated Maize Site.

Comparison of Standardized Drought Indices to Monitor Rapid Onset Agricultural Drought at a Non-Irrigated Maize Site

Hunt, E.D., B. Wardlow, M. Svoboda, K. Hubbard, and T. Arkebauer

ABSTRACT

The Standardized Precipitation Index (SPI) is a robust, standardized index based on long-term precipitation data for a location(s). It has the advantage of being comparably equivalent at different locations over varying time scales and a more accurate classification of extreme events than the widely used Palmer Index. However, the SPI has received criticism for its inability to accurately reflect vegetation conditions during times of significant temperature anomalies because its calculation lacks a temperature component. However, a promising solution appeared with the development of the Standardized Precipitation Evapotranspiration Index (SPEI). The SPEI has the advantage of being a standardized drought index with temperature inclusivity.

The objective of this paper is to evaluate the utility of the SPI and SPEI for characterizing rapid-onset agricultural drought conditions, which are difficult to detect and monitor effectively. The 2003 growing season at Mead, NE began with moist and cool conditions that persisted through much of June. During this time, soil water and evapotranspiration (ET) were uniform between the rainfed maize (RMS) and irrigated maize fields (ICM, IMS). However, a prolonged period of minimal precipitation and heat led to a rapid decline in soil water at RMS. The reduction in soil water led first to reductions in ET and then to a significant gap in yield compared to ICM and IMS. The 2003 growing season was an example of flash drought that had detrimental agricultural impacts. Thus, this paper uses the aforementioned measurements as validation for the effectiveness of using the SPEI vs. the SPI for purposes of flash drought detection. Preliminary results show the short-term SPEI was a more robust indicator of flash drought than a short-term SPI, which implies that drought development is accelerated by a period of heat.