Spatio-Temporal Variations of Heat Wave Characteristics in Different Climatic Zones of Nigeria

Abstract

African countries are highly vulnerable to climate change, especially climate extremes. Heat Waves (HW) (prolonged extreme heat over an area) are projected to become very long and more intense in the upcoming decades and will therefore seriously affect health, infrastructures and especially agriculture that is the main economic activity. This study investigates the heat wave characteristics in different climatic zones in Nigeria over a long period considering the present and the future temperature conditions. The objectives were specified to: analyse the temperature trend in Nigeria, analyse HWs occurrence from 1981 to 2016 in the different climatic zones (Coastal, Tropical Rainforest, Guinea Savannah, Sudan Savannah and the Sahel) in Nigeria, predict the future aspects of HWs to projected 2100 and evaluate the future trend of HW characteristics. ERA-INTERIM reanalysis daily minimum and maximum temperature data from 1981 to 2016 were collected from ECMWF data base and used as the present time. Observation data, 17 stations data were also obtained from NiMet across the country. CORDEX-AFRICA Weather Research and Forecast (WRF) model outputs from 2018 to 2100 were obtained with the same parameters from GSP WACS, F.U.T Akure under RCP4.5 and RCP8.5. Five heat wave characteristics were studied, namely the heat wave number (HWN), duration (HWD), frequency (HWF), amplitude (HWA) and magnitude (HWM) using four definitions: TX90 and TN90 that are temperature based 90th percentile thresholds; Excess Heat Factor (EHF); and the Heat Waves Magnitude Index daily (HWMId). The trend analysis was performed on the observed daily minimum and maximum temperature for the 17 stations. The Modified Mann- Kendall trend test was performed because of the serial correlation in the data, and the results showed significant increasing and significant decreasing trends. The slope was very low in many stations. The study of HW characteristics in different climatic zones revealed that from 1981 to 2016, HWs occurred and covered more zones in the last decades. The Sahel was really affected by the highest number of events and the highest number of days for the duration and the frequency. The HWMId was used to quantify the intensity of HWs in the present time and revealed super extreme HWs in the Sahel and extreme HWs in the South. The prediction using WRF under the two scenarios RCP4.5 and RCP8.5 has shown an aerial increase in the frequency and magnitude of HWs all over the period under consideration. In the 2050s, there will be spatial increase and also an increase in the duration of HWs in almost all the Nigerian land. Even the Coastal zone will be having super extreme (HWMId >= 32) HWs. The RCP8.5 revealed more dramatic and dreadful HWs from 2073. The trend of each of the characteristics using the different definitions under the two scenarios from 1981-2100 revealed significant trends (p-value < 0.05) of many zones and the magnitude of the trends (Sen’s slope) was revealed to be positively very low for some characteristics using some definitions and high (3.5) for other characteristics. Similarly, there are also negative slopes (-0.03). This study could help in agricultural decisions based on climatic zones and also in the infrastructures adjustments and mainly health domain considering that HWs will be more frequent and more intense in the near future time