Observed trends in diurnal temperature range over Nigeria

The long-term trend of diurnal temperature range (DTR) over Nigeria was examined using daily station-based datasets for the period 1971-2013. The results show that the regionally averaged DTR has decreased significantly (-0.34 degrees C per decade) over the Nigerian Sahel (north of 10 degrees N), but there has been a slight increasing trend (0.01 degrees C per decade) over the Nigerian Guinea Coast. The annual decreasing trend of DTR in the Nigerian Sahel is mainly attributable to the significant increasing trend in daily minimum temperature (T-min, 0.51 degrees C per decade), which far outstrips the rate of increase in the daily maximum (T-max, 0.17 degrees C per decade). In contrast, the comparable trends in T-min (0.19 degrees C per decade) and T-max (0.20 degrees C per decade) may explain the non-significant trend of the DTR averaged over the Guinea Coast region. It is observed that the DTR has decreased more in boreal summer (June-July-August) than in boreal winter (December-January-February) for the regions. Furthermore, it is found that the significant DTR declining trend over the Nigerian Sahel is closely associated with an increasing trend of annual and summer precipitation in the region, but the increasing DTR trend in the Nigerian Guinea Coast region can be attributed to the decreasing trend of cloud cover over the region.