A CROP-SPECIFIC DROUGHT INDEX FOR CORN .2. APPLICATION IN DROUGHT MONITORING AND ASSESSMENT

How drought is perceived, and defined, determines the likely response of decision makers to a drought event. Since drought response is usually based on some type of assessment of the severity and duration of the event, a critical clement of a drought response strategy lies in the incorporation of objective and reliable impact assessment techniques. However, a long-standing problem in responding to past droughts has been the lack of reliable techniques for monitoring the drought event and assessing probable impacts. This paper describes a new method to reliably monitor and assess weather's probable impact on corn (Zea mays L.) yields, on a crop reporting district (CRD) level, any time during the growing season. The 1990 growing season was used to demonstrate the ability of the crop-specific drought index (CSDI) to monitor and assess the condition of East Central Nebraska's corn crop every 10 days, starting 17 June, until a definitive projected CSDI value became established. A 3-wk hot and dry spell (24 mm of rainfall during the 3-wk period 28 June-17 July) that immediately preceded silking resulted in a 17 July CSDI assessment, based on the climatological record of the CRD, that projected yields to be only 63% of the maximum yield previously attained in this CRD. However, a substantial rainfall event during the week of silking alleviated the stressful conditions, and by the beginning of the early grain rill period (blister stage), a 6 August CSDI assessment projected the final CSDI value to within 3% of the actual CSDI (projected and actual yields were 86 and 93%, respectively, of the maximum yield previously attained in Nebraska's East Central CRD). The results of this study demonstrate that the CSDI can monitor and assess weather's impact on corn yields on a CRD level.