Empirical analysis of dry spells during growing season with respect to maize crop in Nigeria

Abstract

Dry spell analysis during growing season with respect to maize crop is performed in nine stations in Nigeria. The main data used are daily rainfall, temperature, relative humidity, wind speed, and sunshine hours (1971–2013) from the Nigerian Meteorological Agency (NiMet), Lagos. The same data set (excluding rainfall and sunshine hours) from 0.125° ERA INTERIM Reanalysis (1979–2013) and daily 0.25° horizontal resolution 3B42 rainfall from the Tropical Rainfall Measuring Mission (1998–2013) are obtained to serve as useful supplement to NiMet data. The daily reference evapotranspiration (ETo) is computed using the methodology described in the FAO Irrigation and Drainage Publication 56 with the Penman-Monteith equation. Dry spells frequency and average maize crop evapotranspiration (ETc) for the initial, mid-season, and late season stages for 118 day maize crop variety are computed. Critical onset dates, lengths, and trends are determined during the mid-season growth stage. Mann-Kendall tests are performed on the onset dates and lengths to ascertain statistically significant trends. In the 9 stations, more (less) critical dry spells occurrence of lengths 5–10 and 11–15 days during the mid-season and 5–10 days only during initial stages leading to less (more) maize yield are generally associated with El-Nino (La-Nina) years. The percentage frequency of mid-season spell lengths of category 5–10 days ranges from 4 to 31% for the nine stations. The number of days maize farmers in all the stations could expect first and second critical dry spell occurrences after planting ranges from 35 to 82 and 50–86 days respectively. This finding will aid strategic planning of agricultural operations for enhanced crop yield.