Agricultural and Forest Meteorology 191 (2014) 1–11 Contents lists available at ScienceDirect Agricultural and Forest Meteorology j our na l ho me page: www.elsevier.com/locate/agrformet Monitoring the effects of rapid onset of drought on non-irrigated maize with agronomic data and climate-based drought indices Eric D. Hunt a,f,∗ , Mark Svoboda b , Brian Wardlow c , Kenneth Hubbard d , Michael Hayes b , Tim Arkebauer e a School of Natural Resources, University of Nebraska–Lincoln, Lincoln, NE, United States b National Drought Mitigation Center, School of Natural Resources, University of Nebraska–Lincoln, Lincoln, NE, United States c Center for Advanced Land Management Information Technologies, School of Natural Resources, University of Nebraska–Lincoln, Lincoln, NE, United States d High Plains Regional Climate Center, School of Natural Resources, University of Nebraska–Lincoln, Lincoln, NE, United States e Department of Agronomy and Horticulture, University of Nebraska–Lincoln, Lincoln, NE, United States f Atmospheric and Environmental Research, Inc., Lexington, MA, United States a r t i c l e i n f o Article history: Received 14 January 2013 Received in revised form 31 December 2013 Accepted 2 February 2014 Available online 28 February 2014 Keywords: Soil water Flash drought Stomatal conductance Drought index Evapotranspiration Gross primary productivity a b s t r a c t The 2003 growing season at Mead, NE began with moist and relatively cool conditions that persisted through most of June. During this moist phase of the season, soil water and parameters such as evapo- transpiration (ET) and gross primary productivity (GPP) were nearly identical between a rainfed maize site (RMS) and an irrigated maize site (IMS). A drying phase began in late June, causing decline in soil water at RMS and the necessity of irrigation treatments at IMS. The drying phase turned into a “stressed” phase by early August, as only 10 mm of precipitation fell in a 40-day period between mid-July and late August. Conditions at RMS began to deteriorate even more rapidly after maize entered the critical repro- ductive stage, as the depletion of soil water led to (implied) reductions in stomatal conductance, which led to significant reductions in ET and GPP, compared to the well-watered IMS. Two drought indices, the Standardized Precipitation Index (SPI) and the Standardized Precipitation Evapotranspiration Index (SPEI), were utilized to show the effectiveness of short-term indices at detecting flash drought versus field measurements. Results showed that both the 1-month SPI and the 1-month SPEI were quite sensi- tive to the onset of the flash drought and closely followed the decline in soil water and other biophysical parameters at RMS relative to IMS. Significant precipitation returned and led to some recharge prior to harvest but was far too late to be of any help to the maize at RMS, as the yield difference of 6.3 Mg/ha between RMS and IMS revealed the detrimental effects of a rapid onset of drought during the critical reproductive stage of maize. © 2014 Elsevier B.V. All rights reserved. 1. Introduction Soil water is an integral part of the hydrologic cycle and a crit- ical parameter for plant growth and development. Dale and Shaw (1965) reported that soil water is one of the most critical factors for crop development and yield. Soil water stress at the silking stage of maize (Zea mays L.) can reduce grain yield by 50% (Denmead and Shaw, 1960) and an omission of a single irrigation treatment at a critical stage could reduce maize yields by up to 40% (Cakir, 2004). Meyer et al. (1993) reported that maize was most sensitive to water stress in the silking-blister dough stage and Calvino et al. (2003) showed a curvilinear response of maize yield to available water ∗ Corresponding author at: Atmospheric and Environmental Research, Lincoln, NE, United States. Tel.: +1 402 294 3616. E-mail address: ehunt@aer.com (E.D. Hunt). in the three weeks preceding and following silking. Earl and Davis (2003) reported maize yield reductions up to 85% during severe water stress that occurred after the sixth leaf stage in Georgia. Thus, it is well established that a lack of soil water causes stress and yield reduction in maize. But soil water is not a commonly measured variable at NOAA Cooperative (COOP) weather stations and there are but a handful of networks around the United States where soil water is a standard, quality controlled observation (Hollinger and Isard, 1994; Illston et al., 2008; Hubbard et al., 2009). Drought is a natural, recurring phenomena that occurs every- where at various points in time and is occurring somewhere on Earth at any given point of time. Drought is a complex topic with ecosystem impacts that vary with its intensity and duration and socio-economic impacts that often magnify problems for the most vulnerable members of society. Perhaps it is fitting that drought does not have a universal definition and is often considered in the context of four broad categories defined by Wilhite and Glantz 0168-1923/$ – see front matter © 2014 Elsevier B.V. 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