published in the Pacifica Tribune June 12, 2019
Politics Distorts the Science of Floods
At the confluence of the Missouri and Mississippi Rivers, native American “mound builders” built Cahokia, the largest city in pre-Columbus America. The purpose of their mounds is still debated. Were the mounds refuges from frequent floods, strategic defenses from hostile attacks, or monuments to ruling elites? I suspect all of the above. During warmer and more arid times with minor flooding, Cahokia’s population expanded. By 1250 AD its population equaled contemporary London or Paris. Charles Mann wrote about Cahokia in his superb book 1491 , “the kings who gained their legitimacy from claims to control the weather, would face angry questions from their subjects” when the catastrophic floods returned. Indeed, as severe flooding increased, Cahokia was eventually abandoned.
|Great Flood of 1927 Mississippi River|
Eerily, in the wake of the 2019 Mississippi River Valley flooding, politicians are similarly telling flood victims that their climate policies can also control the weather. Washington’s Governor Inslee tweets, “For the people of Davenport, Iowa, climate change is personal. It’s destroying their homes, harming their communities, and hurting their livelihoods. We must defeat the climate crisis to protect our fellow Americans.” Senator Warren tweeted, “the consequences of climate change are severe, and they are already affecting places like Burlington, Iowa. We have a moral responsibility to act.” But these politicians ignore the science and long history of the Mississippi’s floods.
Investigating causes of Cahokia’s abandonment, scientists uncovered natural climate cycles
governing the region’s flooding. Large floods were common between 300 AD and 600 AD. Then between 600 AD and 1200 AD more arid conditions prevailed. But after 1200 AD severe flooding returned. Natural ocean oscillations can explain alternating patterns of dry and wet periods. So accordingly, the Intergovernmental Panel on Climate Change (IPCC) expresses low confidence regards any global warming effect on modern flooding.
Over the Atlantic Ocean exists a large and somewhat permanent atmospheric pressure system named the North Atlantic Subtropical High (NASH), or Bermuda High. Its clockwise rotation critically effects the climate of the eastern United States. NASH is the reason the eastern United States experiences very humid summers in contrast to the dry west because on NASH’s western edge, warm moist air from the south is pumped northward. More importantly, NASH regulates regional droughts and floods. NASH naturally shifts locations over decades driven by natural ocean oscillations like El Nino. When NASH shifts further to the west, more moisture from the Gulf of Mexico is pumped into the Great Plains causing more floods. When shifted further east, the Midwest suffers more droughts.
Non-scientific journalists and media talking heads falsely insinuate recent extreme flooding is due to global warming. They parrot a single fact that “warmer air can hold more moisture”. Although true, that fact is grossly misapplied. The earth’s warmest air temperatures happen over deserts, but there the air is bone dry. The key to extreme rainfall is not temperature, but how much moisture is transported from the oceans to the land. During cooler times, severe Mississippi Valley floods were observed in 1809, 1829, 1844, 1851, 1874 and 1882. The Great Flood of 1927 is considered the Mississippi Valley’s greatest modern flood. Due to the transport of excessive moisture from the Gulf, average rainfall nearly doubled in 1927.
In contrast to global warming predictions, the Mississippi River Valley also experienced below average winter temperatures and above average snowfall in early 2019. The National Weather Service issued early warnings that the melting snow could cause flooding. They further warned the frozen ground and saturated soils wouldn’t absorb the excess water, additionally swelling streams and rivers.
So many farmers are rightfully rejecting the politicians’ climate claims. Instead farmers blame the Army Corps of Engineers for breached levees and improperly managing levee systems. Levees had seduced people to move into the flood plains. People assumed those levees would always be maintained. But worse, the levee systems unintentionally elevated flooding probabilities.
Each year high water levels from snowmelt and spring rains cause rivers to approach flood stage. Excess water would normally get stored on natural floodplains, minimizing downstream floods. But when levees deny a river’s access to its flood plains, higher volumes of flood water get shunted downstream. Instead of allowing flood waters to spread out, levees narrow a river’s channel width, forcing the river to rise much higher than normal. Thus researchers had warned, “river engineeringhas elevated flood hazard on the lower Mississippi to levels that are unprecedented within the last five centuries.”
Blaming CO2climate change only misguides attention from these real problems. If politicians sincerely hope to promote wise flood protection, they better educate themselves regards natural climate cycles and the unintended consequences of separating rivers from their flood plains.
Jim Steele is retired director of the Sierra Nevada Field Campus, SFSU