El Niño, the cyclical weather phenomenon that began last July and August, has been declared over across Asia as weather bureaus from Hong Kong to the Philippines report that sea temperatures have returned to normal. The phenomenon's flip side, La Niña, appears to have begun, bringing with it heightened rainfall and problems of a different kind.

The El Nino that just abated began in March of 2009, when trade winds began to weaken across the entire breadth of the tropical Pacific Ocean, causing the tide of sea water across the thousands of kilometers of the Pacific to slow and begin to heat up in the sun. The climactic conditions that produce the weather phenomenon are called in Spanish "the child," because sharply warming ocean temperatures arrive off the coast of Ecuador every seven or eight years around Christmas, the birthday of Christ.

In the Philippines, Indonesia, northern Australia and other regions, El Nino produced draught conditions. Across the Pacific in California, the current El Nino ended a three-year drought and pushed snow pack levels to near normal in the Sierra Nevada Mountain range. Water levels in some California reservoirs were reported to be rising as much as four to five feet a day as a series of wet winter storms slammed into the state.

The 2009 El Nino was not a particularly severe one. Nonetheless, drought in the Philippines, for instance, is estimated to have cost at least US$175 million in crop damage, primarily in damage to rice and corn, with the loss of as much as 300,000 metric tons of rice in a country that is one of the world's biggest rice importers.

El Nino began to weaken in January, according to the Hong Kong Weather Observatory, which said that sea surface temperatures had returned to normal by May, with the possibility that a La Nina – of cooler waters – will develop in the second half of 2010.

As with El Nino, La Nina brings mixed blessings. The drought that plagued the Philippines, causing widespread brownouts because of a lack of electricity produced by hydropower, can be expected to abate to some extent although the Philippines' power shortages are chronic and caused by inadequate infrastructure.

Nomura strategist Sean Darby, writing in a research note on June 18, said that the return of La Nina "is likely to create havoc once again for investors. The last time La Nina struck it badly disrupted plantings and harvest in Latin America sending soft commodity prices higher whilst the southern US states experienced terrible drought conditions.”

An April, 2009 study by the Asian Development Bank, titled "The Economics of Climate Change in Southeast Asia: A Regional Review said that La Nina has often caused massive flooding in major rivers in Southeast Asia, and that the events have become more frequent, causing extensive loss in livelihoods, human life and property that weather scientists attribute to global warming.

In Indonesia, according to the ADB report, floods caused by La Niña in 2003–2005 resulted in US$205 million in damage, while in the Philippines the floods caused severe runoff, flooding, and damaging landslides. Between 1991 and 2006, the report said, as many as 10,000 people died in flash floods and landslides. From 975 to 2002, intensified tropical cyclones caused an annual average of 593 deaths and annual damage to property worth $83 million, including damage to agriculture of around $55 million.

Thailand was also hit. In 2001, 920,000 households were affected by floods and the country claimed to have suffered more than $1.75 billion in economic losses related to floods, storms, and droughts in the period 1989—2002. The majority of these losses came from the agriculture sector where crop yield losses amounted to more than $1.25 billion during 1991—2000.

Vietnam also reported serious damage and losses from extreme flooding in the country's Red River and Mekong Deltas and the central region. From 1996 and 2001 alone, millions of houses were damaged by floods including thousands of classrooms and hundreds of hospitals, the ADB report said, ascribing the deaths of 1,684 people to the weather phenomenon as well as damage to rice-growing areas ranging from 20,690 hectares to 401,342, with thousands of hectares of farmland, and fish and shrimp ponds flooded and destroyed, with total estimated damage at $680 million.

"Projected maximum and minimum monthly flows in major river basins in Southeast Asia suggest increased flooding risk during the wet season and increased water shortages during the dry season by 2100,” the report said, with the maximum monthly flow of the Mekong River projected to increase between 35 percent and 41 percent in the basin and 19 percent in the delta.

La Nina is no picnic. The 1998 model resulted in floods in Bangladesh and China that displaced 230 million people according to the David Suzuki Foundation, a science-based Canadian environmental foundation.