SoylentNews

An Anonymous Coward writes:

I've been trying to make sense of the extreme precipitation that hit southern China in the past month, which has produced catastrophic flooding [ibtimes.co.uk], particularly in cities and towns located along the Yangtze River.

El Niño [atavist.com] refers to the periodic warming of surface temperatures in the tropical Pacific Ocean; this phenomenom occurs every few years and typically lasts about a year. (La Niña refers to the opposite, i.e. a periodic cooling). The occurrences have varied greatly in intensity. The National Oceanic and Atmospheric Administration (NOAA) has developed a metric called the Oceanic Nino Index [climate.gov] (ONI), which denotes the deviation from the usual ocean surface temperature, as measured in a region ("Niño 3.4") centered at the equator in mid-Pacific longitudes. NOAA meterologists classify an El Niño period as weak, moderate, strong, or very strong (the last has been dubbed "Super El Niño" by the press), based on whether its peak ONI exceeds 0.5°C, 1.0°C, 1.5°C, or 2.0°C (ONI historical chart here [ggweather.com]).

A Super El Niño ended this past May [weeklytimesnow.com.au], producing warm water that evaporates and circulates through the atmosphere by convection. During an El Niño, the normal Pacific trade winds are disrupted. [iflscience.com] But an obvious question is, why did extreme rainfall occur after the El Niño was over? It seems that the atmospheric turbulence continues for months after the ocean surface temperatures have abated.

Collectively, El Niño and La Niña are referred to as ENSO (El Niño-Southern Oscillation). The late British scientist Gilbert Walker discovered the relationship between surface temperatures and atmospheric pressure in the tropical Pacific; he called it the "Southern Oscillation", so 'ENSO' is partially a tribute to him. One might expect that El Niño would produce average or increased precipitation everywhere, but in fact, the impact varies across the world [columbia.edu], with droughts more likely in Australia for example.

Since the last Super El Niño devastated southern China in 1998, the massive Three Gorges Dam [businessinsider.com] has been constructed on the upper Yangtze River for hydropower and, as a subsidiary benefit, flood control. However, mistakes have been made, such as the draining of large numbers of wetlands [caixin.com] in and around Wuhan (pop. 8.3 million) for residential housing. The wetlands provided an important buffer for flood control; now many have been paved over. And expensive drainage networks [theepochtimes.com] have fallen far short of design goals, much to the disgust of residents.

Science fiction author Robert Marston Fanney, who blogs on climate issues under the name Robert Scribbler, posted his analysis [robertscribbler.com] of El Niño and the Yangtze River flooding just before the Nepartek typhoon hit Taiwan (but after the Wuhan floods).

Original Submission