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Cloud Seeding, Will It Save Us From Water Poverty?

Some 1.2 billion people or 20% of the world’s 7 billion-population, are prone to diseases due to water poverty. Anthropologists dub some of whom as “water-refugees”. This is because they don’t only lack water, but they are on the move across borders in search for water.

The assessment comes from the International Water Management Institute (IWMI) and Earthscan. They produced the 2007 “Water for Food, Water for Life: An Assessment of Water Management in Agriculture”.

The continuing severity of water shortage has led Fred Pearce, author of the globally-recognized book “When the Rivers Run Dry” to conclude that, “the world water crisis has caught us unaware.”

Pearce says: “With a series of local hydrological pinch-points rapidly escalating into a global pandemic of empty rivers, dry boreholes, and wrecked wetland. There is very little we can do to reverse the situation.”

How serious is the water problem worldwide? IWMI defines water scarcity as human’s’ inability to secure and access safe and affordable water for drinking, washing, and food production that affects 1/4 of the world’s area.

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Sandra Postel of the World Watch Institute warned there will be potential water wars. Using the UNFAO and UNICEF figures, the IWMI announced that in the water-starved regions, more than 1 billion people live below the one dollar a day poverty line, majority of whom are women and children.

The majority of them have no access to improved sanitation. The report added that the reason behind these is the lack of water and long absence of rain.Cloud Types

Rainfall Absence & Biodiversity Extinction

According to IWMI, out of the world’s more than two billion hungry people, 850 million are dependent on agriculture. Their agriculture is dependent on rain for irrigation.

In the Sub-Saharan Africa, 95 per cent of farmers rely on rain, as well as 90 per cent in Latin America, less than 70 per cent in the Near East and East Africa, in addition to 60 per cent in South Asia, while, in Southeast Asia, the picture is more mixed.

The statistics mean that some yields from crops such as tubers which is a staple crop, have decreased significantly.  People dependent on rain-fed agriculture are highly vulnerable to both short-term (2-3 weeks) and long-term (seasonal) droughts, the IWMI report explained.

But not only are humans but also biodiversity is suffering as well. The Millennium Ecosystem Assessment reported that diminishing water availability has devastated many ecosystems.

It said some 500 to 1,000 vertebrate species suffer in tropical and subtropical moist broadleaf forests. After them comes those in grasslands and shrublands. Afterwards, those in desert and xeric shrublands, followed by the ones native to tropical and subtropical grasslands. That’s in addition to savannas and tropical and subtropical coniferous forests and mangroves.

Wanted: Magic from Sky

The absence or shortage of rainfall has been of increasing concern since the 1970s. One of the most popular weather modification discoveries is cloud seeding. This method initiates rainfall by targeting clouds. Seeding can occur from an aircraft or from the ground with as silver iodide, dry ice and salt.

But if cloud seeding works, why isn’t it implemented in many of the world’s regions that are water scarce? “Simple, there aren’t enough clouds or there is unfavorable cloud formation. Cloud seeding cannot happen without clouds”, a scientist from the Philippine Atmospheric, Geophysical and Astronomical Services Administration (PAGASA), said.

“Artificial rainmaking, one must understand, aims to create rainfall by inducing precipitation in clouds”, he said. The use of silver iodide salts or dry ice is useless without cloud presence, he added.

Scientists from the Australian Commonwealth Science and Industrial Research Organization (CSIRO) said cloud composition, temperature and cloud diversion also have direct relationship to the success of artificial rainmaking.


Clouds are classified according to their appearance and height from the ground. This classification system is: 1) Cirro. 2) Alto. 3) Strato. 4) Nimbo. 5) Cumulo.

How Does It Work?

A World Meteorological Organization (WMO) primer explains that not all types of cloud favor cloud seeding. The most likely to allow artificial rainmaking are Cumulus Clouds, a cauliflower-like type of clouds.

The cloud forms from updrafts of warm, moist air into an atmosphere that is unstable. Intense daytime heating of the near-surface layer of air, or a wedge of cold air moving across the state (as a cold front), usually triggers the formation of convective clouds.

Normally, a small percentage of cumulus clouds are needed to yield an appreciable amount of rainfall. But these clouds that do produce rainwater are often inefficient.


For all the moisture they incorporate from below, only a tiny fraction of that moisture (as cloud droplets) is ever used to grow large raindrops, which ultimately fall to the ground as rainfall.

Tiny cloud droplets must collide with neighboring droplets enough number of times to yield larger drops and eventually rainwater. Seeding, using silver iodide is placed in the upper portion of the growing convective cloud rich with supercooled droplets. The silver iodide crystal can grow rapidly by tapping that vast field of available moisture.

Because the vapor pressure gradient over ice is less than that over water, the crystal such as silver iodide will more readily attract the tiny cloud droplets. In a matter of moments, the ice crystal transform into a large raindrop which is heavy enough to fall through the cloud mass as a rain shaft.

The silver iodide particles are released from below cloud base, using the strong updraft of the cloud to transport the “seeds” high into the core of the cloud where supercooled cloud droplets are plentiful.

To seed clouds, pyrotechnics or flares consisting of silver iodide burn while mounted on the wings of an aircraft that maneuvers within the updraft field below the bottom of the cloud.

Seeding Time

At times the seeding material can be dispensed below cloud base from an aircraft that is equipped with wing-tipped generators that contain a solution of acetone mixed with seeding material.

Cloud seeding can take place above the cloud top, using an aircraft equipped with a rack containing pyrotechnics. These droppable flares are ignited as they fall from the plane’s belly into the upper region of seedable convective clouds.

Either way, from above cloud top or below cloud the base, seeding with silver iodide gives an ample number of “seeds” with which to grow rainwater: one gram of silver iodide can supply as many as ten trillion artificial ice crystals!

For now, many countries continue to conduct researches and studies on more effective methods of producing artificial rain because the demand has become greater especially for agricultural and domestic use. Others, like China, in fact claim to have done the opposite; stop rains, rather than produce some, which actually happened during the Beijing 2008 Olympic Games.

But meteorological science is more concerned in producing water in light of the worsening climate changes. Water productivity policies dot many countries’ national plans and these include looking at cloud seeding either as a band-aid or cure-all for their water headaches.

This article is from Science’s archive and we’ve originally published it on an earlier date.