The Role of Wind in Rainwater Catchment and Fog Collection

Water droplets in the atmosphere typically range in size from the smallest cloud or fog droplets, with diameters of Im, to the largest raindrops with diameters of about 5 mm. The fog droplets have negligible fall velocities and their trajectories are determined by the speed and direction of the wind. Raindrops have fall velocities (2 to 9 m/s) comparable to typical wind speeds and. therefore, will fall at an angle, except in unusual circumstances where the wind speed is zero. An understanding of the fall angle of rain and drizzle drops can lead to a better orientation and design of rooftop rainwater catchment systems and, in certain environments. to the collection of substantially more water This leads to Jive recommendations: first, that as the wind speed increases or the drop sizes decrease, the vertical component of rainwater catchment systems should be enhanced; second, wind direction, wind speed, and rainfall rate information should be used to optimize the orientation of the house and the shape and slope of the roof; third, that use should be made of upwind walls of houses as rain collectors; fourth, that in foggy environments rainwater catchment systems be modified to collect fog water as well; anafifth, that tree plantations in arid regions should be designed in a manner that optimizes their role as fog collectors.