14 October 2007

River impacts

In this post from planet doom?, the possibility of enhanced flooding along rivers due changes in water uptake from vegetation was briefly noted. In general, rivers face many dangers from both our current environmental management practices and climate change. A few recent items below highlight these threats.

A new study suggests that many rivers impacted by dams or extensive development will require significant management interventions to protect ecosystems and people, Because of the changes in the flow of rivers globally wrought by damming and/or development, most have a diminished capacity to adjust to the changes expected with global warming.

The changes to river systems are expected to vary -- some are expected to have large increases in flood flows while other basins will experience water stress such that there is not enough water to meet human needs. For example, by the 2050's, mean annual river discharge is expected to increase by about 20 percent in the Potomac and Hudson River basins but to decrease by about 20 percent in Oregon's Klamath River and California's Sacramento River

Recent news items demonstrate some negative effects of human 'management' of river systems, even before we have felt the full brunt of climate change. This news article reports that 15 000 wildebeest dies while crossing the Mara river in Kenya. Such a mass death was the first of its king in recent memory. Many of the animals died as a result of being trampled. Some officials blame the destruction of the nearby Mau forest for changing weather patterns and affecting tide levels, and they called on the government to curb the deforestation.

The Three Gorges dam in China is also proving to be an 'ecological disaster', even before it is fully completed. The water quality of the Yangtze's tributaries is deteriorating rapidly, as the dammed river is less able to disperse pollutants effectively. The incidence of algae blooms have risen steadily since the reservoir was completed in 2006. The rising water is also causing rampant soil erosion, resulting in riverbank collapses and landslides along the shores of the Yangtze's tributaries.

These events illustrate examples of the dangerous secondary effects we have seen with our current environmental degradation. Climate change will likely exacerbate these effects. The inter-linkages within the biosphere means that even relatively simple alterations to the environment are likely to have unforeseen consequences. Great care is required if we want to avoid the worst follow-on effects. This especially applies to climate change, about which we are woefully ignorant and arrogantly overconfident -- a dangerous combination. The time is now for prudent action to (try to) pull back from the brink of dangerous climate change, before it is too late for future generations.

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