Trends and variability in absolute indices of temperature extremes over Nigeria: linkage with NAO

Abstract

ABSTRACTThe present study examines trends in extreme temperature absolute indices [warmest day (TXx), coldest day (TXn), warmest night (TNx) and coldest night (TNn)] using the newly homogenized daily minimum and maximum temperature series from 21 stations in Nigeria for the period 1971–2012. The indices provide an understanding of the characteristics of changing temperature, in light of the present anthropogenic global warming. Trends in the indices and the statistical significance are obtained using the modified Mann–Kendall test in the R‐package. The results show that many of the stations have significant increasing trends in the absolute indices, with the warming most pronounced in Southern Nigeria. Averaged over the country, the TXx, TXn, TNx and TNn have absolute warming trends of 0.59, 0.17, 0.67and 0.97 °C, respectively, for the 42 years since 1971. The warming rate is highest during the winter (DJF) season for TNn. The present study also examines the possible influence of large‐scale teleconnection patterns on extreme temperature variations by determining the correlation between the absolute indices and the North Atlantic Oscillation (NAO) index on monthly, seasonal and annual timescales. Our results show that warming over Nigeria during the dry season months from November to February is significantly correlated with NAO. The NAO has significant correlation with TXx and TXn in the north, and with TNx and TNn in the south. The analysis is repeated with ERA‐20C‐gridded data set, and similar correlations are found. The warming nights, in particular, in Nigeria can lead to sleeplessness and widespread mosquito‐related diseases as the mosquito population and its parasites thrive in warmer conditions. The results of the analyses are relevant for decision‐making process, especially for the development of early warning systems for extreme heat events.