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BURSZTYN: Flooding, humanity and the circle of life

'It’s time we understood climate change has other, less obvious effects. We may not realize they are occurring, but they are likely to cause unexpected problems' writes science columnist
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Prior to the completion of the Aswan High Dam in June 1970, the River Nile flooded every year. The flood was caused by the Blue Nile draining Ethiopia following its annual rainy season’s drenching.

The Nile’s other branch, the White Nile, is steady through the year, largely because it flows through a vast wetland, Sudan’s Sudd. This immense wetland expands to absorb the water from Uganda’s rainy season and shrinks in the dry season, thus moderating the While Nile’s flow into Sudan.

Long before there were Egyptians, the annual Nile flood was important to the country’s wildlife. Local fish evolved to breed during the flood. The newly water-logged land was cleansed as insects emerged from their waterlogged burrows. They, in turn, sustained the newly hatched fish.

As people settled the valley of the Nile, they began to adopt “recession agriculture.” They would seed their land as the flood water receded. Their crops were bountiful partly because of the rich silt — soil eroded from Ethiopia’s highlands  left behind by the flood water. All those fish pooping in the water helped, too.

The life of ancient Egypt’s people synchronized with the Nile’s annual inundation. Not only did farmers plant as the flood receded, but they became fishermen when they were not tending their crops. (A similar, flood-dependent lifestyle also developed in southern Mali, along the Niger River.)

The annual flood was important to ancient Egyptian civilization. Measuring devices, called “Nilometers,” were devised to measure its height and duration — a reliable guide to that year’s harvest. Before Nilometers, priests discovered they could predict the flood via astronomy. About a week before the river began to rise, Sirius, the Dog Star, could be spotted on the horizon just before sunrise. Within a week of this sighting, Sirius would rise too late to be seen at dawn; the brightening sky would make it invisible.

Timing is probably universal in biology. In some tropical regions, living organisms synchronize with the rain, in temperate regions some are timed to day length, others to temperature. One example is the flowering of trees. Usually triggered by a series of warm days, if flowers open too early, they risk damage from frost, or perhaps their insect pollinators have not yet appeared. Either way, fruiting is likely to be affected.

In the Arctic, plant growth only begins when snow has melted. Due to unusual warmth, the spring migration of Arctic caribou may occur after peak plant growth. In other Arctic regions, the hatchlings of migrating geese may miss out on peak vegetation. When this happens, reproductive success is reduced, often dramatically.

Closer to our climatic zone, the European pied flycatcher winters in sub-Saharan Africa, migrating north to Europe in spring. Their egg laying is timed for hatchlings to emerge when oak leaf-munching caterpillars are at their peak. The parent birds have been logged delivering 60 caterpillars per hour to their chicks, which use the bonanza to fledge in two and a half weeks. If the chicks hatch too late for “peak caterpillar,” reproductive success will be affected. Recently, this has been happening in the Netherlands, where the pied flycatcher population is down by 90 per cent. One can imagine people being upset by the defoliation of their trees.

Studies have identified problems for other birds, too. One study reported migrating birds setting off south late because the Arctic was uncharacteristically warm. However, the food resources they expected along their migration route were reduced; that same warmth caused tree fruit to ripen early and fall off. Not only did the birds suffer, but the fruit trees missed their seed-dispersal service.

Alaska pollock have been spawning early, and missing the peak plankton bloom. This has upset their main predator, humans, who make them into McDonald’s Filet-O-Fish. Elsewhere along the north Pacific coast, various species have been spawning too early or too late to best exploit their food resource, and climate change has been blamed. Meanwhile, hot summers along North America’s east coast have led lobsters to migrate inshore early. Very large catches caused prices to collapse, an equally disruptive problem.

We have become aware of the exceptional heat wave now affecting Europe. It’s time we understood climate change has other, less obvious effects. We may not realize they are occurring, but they are likely to cause unexpected problems. The mistiming of biological events has the potential to be far more serious than we can imagine.

Peter Bursztyn is a self-proclaimed “recovering scientist” who has a passion for all things based in science and the environment. The now-retired former university academic has taught and carried out research at universities in Africa, Britain and Canada. As a member of BarrieToday's community advisory board, he also writes a semi-regular column. If you have a question Peter might be able to answer or something you're curious about, email us at news@barrietoday.com.