“A robust result, consistent across climate model projections, is that higher precipitation extremes in warmer climates are very likely to occur.” — IPCC
“As the climate has warmed… heat waves are longer and hotter. Heavy rains and flooding are more frequent. In a wide swing between extremes, drought, too, is more intense and more widespread.” — Climate Communications
It’s a tough fact to get one’s head around. But a warming climate means that many regions will both experience more extreme droughts and more extreme floods. The cause for this new weather severity is that a warming planet produces higher rates of evaporation together with more intense atmospheric convection. Warmer air over land means that the moisture gets baked out of terrain, lakes and rivers faster. And this warming effect causes droughts to settle in more rapidly, to become more intense than we are used to, and to often last for longer periods.
(As the climate warms, instances of extreme weather — both droughts and floods — increase. Image source: NOAA/UCAR.)
On the flip side of this severe weather coin, more moisture evaporating from the world’s lands and oceans means that the atmosphere contains a greater volume of moisture overall. This heavier moisture load enters a hotter, thicker, taller lower atmosphere (troposphere). One that is becoming increasingly stingy about giving up that moisture in the form of precipitation much of the time. All that heat and added convective energy just serves as a big moisture trap. So the load of moisture has to be heavier, overall, to fall out. When the atmospheric moisture hoarding finally relents, it does so with a vengeance. Thicker clouds with higher tops drench lands and seas with heavier volumes of rain and snow. And when the rain does fall from these larger storms, it tends to come, more and more often, in torrents.
California Record Drought to Record Flood in Just 4 Years
A set of facts that were drawn into stark relief recently in California which over the past few years experienced one of its driest periods on record but, in 2017, is on tap to see its wettest year ever recorded for broad regions. In a section of hard-hit Northern California, the cumulative 2017 rainfall average had, as of yesterday (April 9), hit 87.5 inches. The record for the region in all of the past 122 years is 88.5 inches for the entire year.
It is just early April. But the region tends to receive most of its moisture from January through March. However, all it would take is a relatively minor storm system to tip the scales into record territory. And it now appears likely that this region will see in excess of 90 inches for the present year.
Infrastructure damage from this year’s flood for the state is likely to considerably exceed $1 billion. Damage to roads alone is nearly $700 million. And that does not include stresses to dams — like the one at Lake Oroville where an eroded spillway threatened structural integrity and forced 200,000 people to evacuate. Overall, the cost of the repairs combined with the cost of hardening California’s infrastructure to these new extreme weather events could top $50 billion.
New Zealand — Debbie Brings 500 Year Flood Event with More to Follow
In New Zealand, a Tropical Storm Debbie (which struck Australia as a Category 4 Hurricane and flooded 1,800 homes in the town of Rockhampton) engorged with the extraordinarily high volume of moisture evaporating from the very warm waters of the Pacific Ocean produced a rain event that, under normal climate conditions, would have occurred only once every 500 years. The storm blanketed much of New Zealand with strong winds and heavy rains — sparking flooding and power outages. On North Island, the system hit a new extreme as it dumped a record two months worth of rain (7.5 inches) in just two days upon the town of Edgecumbe. The torrent swelled the nearby Rangitaiki River, forced a levee breach, flooded the city, and spurred thousands of residents to evacuate.
(Cyclone Cook takes aim at New Zealand and a link-up with a trough dipping through the region. Image source: LANCE-MODIS.)
Across New Zealand, flooding damage estimates from the event are expected to considerably exceed 1 billion dollars and could track into the billions.
Meanwhile, Cyclone Cook, similarly engorged with moisture, is in the process of combining with a large trough extending down from the Southern Ocean and over New Zealand. Cook is predicted to track toward New Zealand across ocean waters that are 1-2 C warmer than normal over the next few days. It is expected to feed energy into a long frontal system extending up from the ocean region just north of Antarctica. Present model predictions indicate the potential for extremely high cloud moisture loading in the range of 3.5 kilograms of water per square meter over parts of North Island near Tauranga in the 26-30 hour time-frame. A worrisome potential extreme precipitation hot spot in a mated system that is expected to again blanket New Zealand with flooding rains over the next three days.
Peru, Colombia, Ecuador Floods
In isolation, each of these extreme events would be odd enough. But right now the issue is that the heightened frequency and widespread geographic dispersal of extreme flooding is a considerable concern. And to this trend of more widespread incidents, we can add the extraordinarily severe flooding that has impacted several South American nations during early 2017.
(Strong El Nino events are often associated with flooding in western South America. Though an El Nino is expected during 2017, it is predicted to be weak-to-moderate in intensity. So it is likely that the very warm waters feeding extreme rains in the region were given an assist by human-forced climate change. Image source: Earth Nullschool.)
Very warm sea surface temperatures off South America this winter and spring have fed into record rains across Peru, Ecuador and Columbia. In Peru, what was arguably the worst flooding ever recorded for the state during March destroyed tens of thousands of buildings, rendered 700,000 people homeless, resulted in the loss of about 100 souls, and wrecked 6,000 miles of highway and scores of bridges. The number of people made homeless by this single series of extreme weather events is particularly staggering — amounting to about 1 out of every 40 people living in the state. For Peru alone, an estimated 9 billion dollars is now needed to recover.
Nearby Ecuador also experienced record rains. Tens of thousands of acres flooded as 20 people lost their lives and thousands of people were forced to evacuate. And in the Colombian town of Macoa near the Ecuador border, a severe, rain-bomb type, thunderstorm associated with this extraordinarily moist weather pattern unleashed mudslides and torrents of water so violent that 254 victims were unable to escape.
Conditions in Context
(Atmospheric rivers are often associated with extreme rainfall events as was the case with California this winter and spring. Global water vapor tracking enables us to track these atmospheric rivers streaming out from the moisture-rich Equatorial region. Image source: CIMSS.)
It is worth noting that each of these instances of severe rainfall around the globe rank as either the worst on record or nearly the worst on record for the impacted regions. They occur in a similar temporal space but over a widely varied geographical extent. In the instance of apparent cyclone flooding amplification in Australia and New Zealand — very warm and above average sea surface temperatures appear to have been involved. This is also the case with the severe rains seen in South America. In California, a shift in the weather pattern from extremely dry to extremely wet followed a receding of hot ocean conditions and an associated blocking pattern. The warm Pacific waters which pushed storms north into Alaska and Canada instead shifted to a cool-north, warm-south pattern that intensified the storm track and enabled the direction of record high atmospheric moisture plumes near the Equator toward California. All of these various patterns are consistent with what we would expect from a human-forced warming of our climate.
Hat tip to Vic
Hat tip to Climatehawk