The overall reactions at the base of the Tower are easily found from the wind and gravity loads (dead and live). Overall vertical and horizontal reactions will develop to balance the respective loads. A moment reaction will also develop to balance the horizontal load applied through its centroid a distance l/2 from the support.
The reactions at the base of each column, instead of for the Tower as a whole, are necessary to find the internal forces in the individual columns. Each column will logically develop half of the horizontal and vertical reactions found for the entire structure.
The bending reactions in the individual columns will be investigated with the internal forces. The wind force will create a higher vertical reaction in the leeward support and a lower vertical reaction in the windward support because the wind alone would create compression in the leeward support and tension in the windward support.