The study investigates the trends in temperature in the Upper and Lower Niger Basin Development Authority Areas using standardized Anomaly Index, Gaussian Low Pass and Spearman's correlation coefficient. From the data collected and analyzed, the mean annual temperature and mean annual maximum temperature demonstrated pronounced temporal increasing trend in the period 1951-2010 while the mean annual minimum temperature showed no trend. The rate of increase in mean annual temperature, mean annual maximum and minimum temperatures was 0.45˚C, 0.40˚C and 0.20˚C respectively. The mean annual maximum temperature warmed faster than the mean annual minimum leading to increase in diurnal range of temperature. The annual temperature anomaly in the study area tracks the observed anomalies for the Northern Hemisphere in the 20th century. The decadal temperature increase is very small particularly as from 1980.

Using 70 years of daily rainfall records in eight stations, an analysis of variability and trends of daily heavy rainfall events over Niger River Basin Development Authority Area was carried out by using Standardized Anomaly Index and Spearman Rank Correlation Coefficient. Significant temporal variability on interannual and decadal time-scales was observed in the frequency of heavy rainfall events and annual heavy rainfall amount. Both the annual heavy rainfall amount and frequency of heavy rainfall events demonstrated no pronounced temporal decreasing or increasing trend. However, more recent data records from 1981 onwards revealed an increasing trend. Thus, evidence of a temporal change is apparent in heavy rainfall events in the last three decades in sympathy with global warming.

Reliable simulation of turbulent heat fluxes needed for modeling land-atmosphere interactions remains a challenge over the humid tropical region. This may be connected with the inadequate parameterization of the roughness lengths for momentum (z 0m ) and heat (z 0h ) transfer usually expressed in terms of excess resistance factor (κB −1 ). This paper assesses the performance of existing κB −1 schemes developed for high wind speed conditions over the humid tropical region. Thereafter, a more appropriate κB −1 suitable for low wind speed condition is developed for use in the aerodynamic resistance parameterization. Based on observed surface heat fluxes and profile measurements of wind speed and temperature from Nigeria Micrometeorological Experimental site, new κB −1 parameterization was derived through the application of the Monin-Obukhov similarity theory and Brutsaert theoretical model for heat transfer. The derived κB −1 ¼ 6:66 Re 0:02 * −5:47, where Re * is the Reynolds number. Turbulent flux parameterization with this new formula provides better estimates of heat fluxes with reference to results from existing κB −1 schemes. The R 2 increased by about 85%, while mean bias error and root-mean-square error in the parameterized Q H based on the derived κB −1 reduced by about 63% and 66.7%, respectively. Similarly, the R 2 increased by about 38%, while mean bias error and root-mean-square error in the parameterized Q E based on the derived κB −1 reduced by about 47.8% and 52.6%, respectively. The derived κB −1 gave better estimates of Q H than Q E during the daytime. The derived κB −1 scheme corrects a well-documented, large overestimation of turbulent heat fluxes, and it is therefore recommended for use in regions where low wind speed is prevalent.

The development of improved methods for estimating turbulent heat fluxes is important in effective monitoring of the surface energy balance for climate change prediction. However, different  parameterized models carried out at the local site of Nigerian Micrometeorological site (NIMEX-1) did not consider the surface heat fluxes-aerodynamics resistance relationships, and these validated models cannot be incorporated into the Climate models because some of the input climate variables are not routinely available in some meteorological stations. This study therefore, aims at improving the diurnal patterns of surface heat fluxes estimates using radiometric surface temperature and aerodynamic surface-layer resistances. Hourly data of air temperature (Ta), soil temperature (Tsoil), global radiation (QL), surface temperature (Ts), wind speed (u), QH and QE were obtained from the NIMEX-1 at Ile-Ife (7.55 oN, 4.55 oE). The QH and QE were estimated using Aerodynamic Resistance Approach algorithm which was modified to reduce the large bias errors between the aerodynamic temperature and surface temperature above the ground level. The algorithms were validated and rated using the following error statistics: coefficient of determination (r2), Mean Bias Error (MBE) and Root Mean Square Error (RMSE). The RMSE and MBE for the modeled QE estimated using ARM and MAR reduced from 28.33Wm-2 to 14.33 Wm-2 and 36.93 to 10.74 Wm-2 respectively while for QH ,the RMSE and MBE reduced from 17.29 Wm-2 to 9.49 Wm-2 and 31.39 to 16.93 Wm-2 respectively. The r2 values ranged from 0.68 to 0.73 and 0.95 to 0.98 for QH and QE respectively. The MAR had the highest r2 and least error values.  Hence, the proposed modified Aerodynamic resistance models are estimated the diurnal and seasonal turbulent heat fluxes accurately for tropical regions.

Surface temperature (Ts) is vital to the study of land-atmosphere interactions and climate variabilities. However, observed Ts data are still very scarce in humid tropical region. There is therefore a need to parameterize and improve the representation of Ts in Global Climate Models using available meteorological data. Six land surface temperature parameterization approaches (Force restored, Liebethal, Holtslag, Equilibrium Gradient, Tracy and Gottsche approaches) were validated with actual measurements using the Nigeria Micrometeorological Experiment (NIMEX) surface layer observations. The Liebethal approach showed the best agreement with the measured data with average coefficient of determination, mean bias error and root mean square error of 0.96 ± 0.01, 0.08 ± 0.04 o C and 0.85 ± 0.14 o C, respectively, in simulated Ts. The results also showed that the Force restored and Tracy approaches are applicable for land surface temperature parameterization in this region.