DISTRIBUTION OF COOLING DEGREE DAYS AND HEAT INDICES FOR SELECTED STATES IN NORTHERN NIGERIA

Abstract

Cooling degree days (CDD) and heat index (HI) are quantitative indices being designed to reflect the demand for energy requirements to heat or cool a home, business or other issues. These indices are derived from daily air temperature and relative humidity. The study investigates the thermal comfort conditions of some selected states in the Northern Nigeria, by making observations from the derived cooling degree days and heat index values. The spatio-temporal variability of the estimated cooling degree days and heat indices across the selected states in Northern Nigeria, were assessed, and maps indicating the degree of vulnerability and risks were generated. The cooling degree days and heat indices were calculated using monthly temperature and relative humidity data for theselected states. The data were obtained from the Nigerian Meteorological Agency (NIMET), Oshodi Lagos, Nigeria. The monthly temperature and relative humidity data spanned between 1984 to 2013 (thirty years). The stations used are six (6) in number, within the axis of the Guinea, Sudan and Sahel Savanna of Nigeria. Heat indices and cooling degree days methods integrated with Geographic Information System (GIS) were used to determine the extent of thermal discomfort and heat in the region. The cooling degree days were used to estimate the amount of excessive heat load for cooling in these locations during the dry and rainy season. It is observed that energy demand for cooling are high during the dry season in Minna than in other stations, but as the rainy season comes, Maiduguri cooling degree days becomes the highest indicating that cooling energy demand in Maiduguri will be higher than in other stations. The heat indices (HI) values were used to classify the study area into different heat zones namely; ‘No caution (below 26.67oC)’, ‘Caution (26.67 – 32.2 oC)’ and ‘Extreme caution (32.2 – 39.44 oC) zones’. Jos was in the ‘No caution zone’ all year round while Minna was in the ‘caution zone’ all year round. Other stations varied between the ‘No caution zone’ and ‘caution zone’ except for Kano that fell in the ‘extreme caution zone’ in the month of May. This study also examines the variation in heat index and cooling degree degree days during the dry and rainy season spatially. The variations were used to identify and determine the level of heat stress and thermal discomfort and its spatial distribution across the study area. The study concluded that Jos has low cooling degree days all year round. Cooling degree days are observed to be higher in Minna and lower in Maiduguri during the dry season. But during the wet season, it is a contrasting situation as the CDD is lower in Minna and higher in Maiduguri. The heat stress and thermal comfort was lowest in Jos, moderate in other locations such as Kano, Bauchi, Maiduguri and Gusau and highest in Minna.