Effects of Variations in Sea and Land Surface Temperature on Rainfall Pattern over Nigerian Coastal Zone

Abstract

This study evaluated the variations in sea and land temperature from 1901 to 2013 with a view to examining their effects on rainfall pattern in the coastal zone of Nigeria. It used the National Oceanic and Atmospheric Administration (NOAA) monthly mean sea surface temperature (SST) over the Atlantic Ocean (longitude 0^o E - 8^o.20^′ E and latitude 1^oN - 3^o.50^′ N). Land Surface Temperature (LST) and rainfall dataset sourced from the archive of the University of Delaware (UDEL) and ground station observations (NIMET) over four selected coastal locations (Calabar, Lagos, Port-Harcourt and Warri) were also used. The mean observations of rainfall and temperature of NIMET and UDEL for the overlapping period (i.e. 1974-2013) were compared Using paired T-test and Percent Bias. The annual and seasonal trends in these climatic variables were examined using their deviations from means and trend analyses. The study then employed Pearson multiple linear regression analysis to evaluate the combined effects of LST and SST on rainfall pattern over the study areas. The results revealed the highest values of SST and LST in MAM and the lowest in JJA season.  It rained in all months across the stations with the maximum rainfall (163.5 - 471.2 mm/month) in JJA and the least (24.0 - 47.2mm/month) in DJF. The comparison of both UDEL and NIMET observations suggested no significant difference between both datasets at P = .05.  The results demonstrated increasing trends in both SST (0.012^oC year^-1) and LST (0.003 to 0.007^oC year^-1). Both SST and LST significantly influenced rainfall pattern (0.445 ≥ R ≤ 0.731; R > 39%) at P = .05. The contributions of SST to rainfall variations were, however, significantly higher (0.530: 0.422) than those of LST (0.452: 0.215) in Lagos and Port-Harcourt due to the proximity and locations of these stations to the Atlantic Ocean.

Keywords: Sea and land surface temperature, rainfall variations, effects, coastal zone