A study of the electrostatic forces between water droplets may have opened the door to getting rain to fall where we want it, and not where we don't. As powerful a life-saving force as this could be, it would raise the question of who gets to decide what “we” want.

Claiming the power to control the weather, particularly drought-breaking rains, may be one of the oldest deceptions in human history. In the 1950s hopes were high that science could succeed where magic failed. Although rain-making efforts based around seeding clouds with silver iodide particles were not a complete failure, the success rate has been low enough, and the cost so high, that application has been relatively rare.

However, Professor Maarten Ambaum of the University of Reading thinks this may be because we have failed to understand the way water droplets interact in clouds. In Proceedings of the Royal Society A, Ambaum and co-authors offer an alternative model and argue it could become the basis for shocking the sky into releasing the water it holds.

Clouds contain plenty of water vapor but it only rains when this condenses into larger droplets. Aerosols can provide the seeds around which water coalesces, but the study authors argue the charge on droplets and aerosols is also important and overlooked.

The paper demonstrates that even droplets carrying the same polarity of charge (ie both positive or all negative) will be attracted to each other if there is a variation in charge strength. “Charges can migrate,” the paper notes, “and the charges in one drop will induce image charges in the other drop. Those induced image charges will induce further image charges in the original drop, and then again in the second drop, repeating indefinitely, which leads to an attractive force which can dominate if the drops are close to each other.”

As if this wasn't complicated enough, the amount of charge on a drop can change thanks to the acquisition of ions driven by nearby electric fields.

Ambaum and co-authors conclude that adding electrostatic effects adds no more than 5 percent to the rate at which droplets collide and stick together. Nevertheless, this small shift can be the difference between rain falling where it is needed, and water vapor not reaching a critical threshold until it has moved elsewhere.

The authors have been funded by the United Arab Emirates, one of the driest nations on Earth, to investigate adding charge to the atmosphere to see if it will cause rain to fall. They have been experimenting with using drones to deliver the electric fields. However, in places where fog is common, including many deserts, the authors think towers just 10 meters (33 feet) high could do the trick. The authors hope the calculations in their paper will help them identify the ideal amount and timing of charge needed to make it rain.

In a world where both drought and floods are becoming more common and severe, being able to control the weather, even a little, could save millions of lives. This may be safe when rain that would otherwise fall at sea is made to drop where it is needed. On the other hand, one country harvesting rain that their neighbors consider their own could be considered grounds for war, so the world needs to sort out such disputes before the technology arrives.

[H/T: The Guardian]