Clouds With a Dash of Salt: How Science Makes It Rain During Dry Season

(SPOT.ph) Did you know that in the middle of dry season or even drought, it's possible for science to make it rain—literally? 

Cloud seeding, a weather modification technique improving clouds' ability to produce rain even during dry spells, is the Department of Agriculture's multi-million solution (read: P18 million) to alleviate the impending effect of El Niño on crops and fisheries. While this operation can't end the drought or fill dam reservoirs to the brim, it helps increase rainfall during the dry season in a way natural clouds can't during that time, the Philippine Atmospheric Geophysical and Astronomical Services Administration said.

Also read:
Why It's Dry Season, Not Summer in the Philippines, According to Science
Why Does it Get so Hot in Dagupan During the Dry Season?

How does cloud seeding work?

Short answer: Particles such as salt are implanted (or seeded) into clouds to help them generate rainfall.

The longer, more comprehensive explanation: Clouds are made up of tiny water droplets or ice crystals that form when water vapor—which is in a state of gas or moisture—condenses or turns into water of very tiny particles that are present in the air. Without these particles, raindrops or even snowflakes cannot form.

To improve the clouds' ability to produce rain or snow, particles like finely grounded or pulverized salt (sodium chloride) are put into seedable clouds. Salt, which attracts water vapor, acts as the seed upon which cloud droplets form into raindrop sizes and fall back to the ground.

It's been an effective practice for over 50 years in more than 40 countries, according to Philippine Atmospheric Geophysical and Astronomical Services Administration (PAGASA).

Read more: How to Avoid Heatstroke Now That Dry Season Is Here

Cloud seeding activities are multi-agency projects where PAGASA, the implementing agency, works with the following partners: the Philippine Air Force for the cloud seeding aircraft and pilots skilled in cloud seeding; the Agriculture Department's Bureau of Soils and Water Management, which coordinates with local government units, agriculture and water sector, and other groups for their cloud seeding needs; and the Civil Aviation Authority of the Philippines for the air space permits and licenses needed for the project.

First, PAGASA will observe the skies to check if cloud seeding is possible using equipment like satellites, Doppler radar, and radiosonde sounding. Its prediction will also be based on the prevailing weather condition and cloud models. It will then make a decision if it's go-seed, no-go, or on standby mode.

If it's a go-seed day, the aircraft will take off, bringing along the pilot and crew members to the skies for the seeding. If it's a no-go, those involved will monitor the next potential cloud seeding day.

What happens during cloud seeding?

If a cloud seeding is successful, rainfall is observed within 30 minutes to an hour after the operation, according to PAGASA.

Within an hour of seeding, clouds will bring light to moderate rains. An hour and a half after, moderate to heavy rains may be dumped in areas covered by clouds. Three hours after the seeding, the rain cloud will be gone.

Take note that there's no evidence suggesting chemicals used during this project will bring negative impacts on the environment, PAGASA said. The rains from seeded clouds are also no different from natural rainwater from non-seeded clouds, and it cannot change weather patterns as it only changes individual or groups of clouds.

Why can't we just cloud seed often during the dry season?

Several factors need to be considered before a cloud seeding operation gets green light from concerned agencies, according to Teresita Sandoval, a former chief of BSWM's water resources management division, in an interview with ABS-CBN News in March 2019.

Local government units usually request for cloud seeding, but the division will first monitor and coordinate what's happening on the ground before it gives a go signal. It has to factor in the crops planted in a particular area and how badly it is affected by the drought. Affected areas have to be at least 1,000 hectares and it has to have standing crops that need water to save them from total loss, said Sandoval. 

It also has to take note if the crops are sensitive to rain, like mangos and watermelons during the harvesting stage, to avoid damage.