Development of solar ultraviolet radiation distribution map for Tanzania using an empirical model

The purpose of this study was to develop solar ultraviolet radiation maps for Tanzania based on data generated by using an empirical model. An improved empirical model was formulated using global radiation, relative humidity and air temperature parameters as input. The improved model provides satisfactory results with a correlation coefficient of 96 %, an assurance factor (UVest/UVmes) in the range of 0.91 to 1.10 and a percentage error which does not exceed ±10 % when estimated solar ultraviolet radiation values were compared with measured values from two experimental stations. After the validation, the model was used to calculate mean monthly UV radiation over Tanzania by employing input data of the year 2001. Maps for mean monthly solar ultraviolet radiation distribution throughout Tanzania were constructed based on the months of January, April, July and October. Generally, the maps show that Central, Southern, and Southern Coastal Highlands zones received relatively high annual mean solar ultraviolet radiation ranging from 0.632 to 0.702 MJ/day/m2 while North Eastern Highlands, Victoria Basin, and Southern Highlands zones received relatively low UV values ranging from 0.370 to 0.483 MJ/day/m2. Other zones received moderate values of annual mean UV radiation of between 0.485 and 0.610 MJ/day/m2. Also, for the whole country the maximum mean monthly value of solar UV radiation was 0.840 MJ/day/m2 while the minimum value was 0.240 MJ/day/m2. Further study is recommended to improve the accuracy of the model to less than ±10 %.