From Tel Aviv University, another science press release with “could and may” qualifiers: Climate Change May Lead to Fewer — But More Violent — Thunderstorms
Number of flash floods and forest fires could increase with temperature, says TAU researcher
Researchers are working to identify exactly how a changing climate will impact specific elements of weather, such as clouds, rainfall, and lightning. A Tel Aviv University researcher has predicted that for every one degree Celsius of warming, there will be approximately a 10 percent increase in lightning activity.
This could have negative consequences in the form of flash floods, wild fires, or damage to power lines and other infrastructure, says Prof. Colin Price, Head of the Department of Geophysics, Atmospheric and Planetary Sciences at Tel Aviv University. In an ongoing project to determine the impact of climate change on the world’s lightning and thunderstorm patterns, he and his colleagues have run computer climate models and studied real-life examples of climate change, such as the El Nino cycle in Indonesia and Southeast Asia, to determine how changing weather conditions impact storms.
An increase in lightning activity will have particular impact in areas that become warmer and drier as global warming progresses, including the Mediterranean and the Southern United States, according to the 2007 United Nations report on climate change. This research has been reported in the Journal of Geophysical Research and Atmospheric Research, and has been presented at the International Conference on Lightning Protection.
From the computer screen to the real world
When running their state-of-the-art computer models, Prof. Price and his fellow researchers assess climate conditions in a variety of real environments. First, the models are run with current atmospheric conditions to see how accurately they are able to depict the frequency and severity of thunderstorms and lightning in today’s environment. Then, the researchers input changes to the model atmosphere, including the amount of carbon dioxide in the atmosphere (a major cause of global warming) to see how storms are impacted.
To test the lightning activity findings, Prof. Price compared their results with vastly differing real-world climates, such as dry Africa and the wet Amazon, and regions where climate change occurs naturally, such as Indonesia and Southeast Asia, where El Nino causes the air to become warmer and drier. The El Nino phenomenon is an optimal tool for measuring the impact of climate change on storms because the climate oscillates radically between years, while everything else in the environment remains constant.
“During El Nino years, which occur in the Pacific Ocean or Basin, Southeast Asia gets warmer and drier. There are fewer thunderstorms, but we found fifty percent more lightning activity,” says Prof. Price. Typically, he says,we would expect drier conditions to produce less lightning. However, researchers also found that while there were fewer thunderstorms, the ones that did occur were more intense.
Fire and flood warning
An increase in lightning and intense thunderstorms can have severe implications for the environment, says Prof. Price. More frequent and intense wildfires could result in parts of the US, such as the Rockies, in which many fires are started by lightning. A drier environment could also lead fires to spread more widely and quickly, making them more devastating than ever before. These fires would also release far more smoke into the air than before.
Researchers predict fewer but more intense rainstorms in other regions, a change that could result in flash-flooding, says Prof. Price. In Italy and Spain, heavier storms are already causing increased run-off to rivers and the sea, and a lack of water being retained in groundwater and lakes. The same is true in the Middle East, where small periods of intense rain are threatening already scarce water resources.
I’m not sure why they think this is news, a nearly identical study was done back in 2007 and published in PNAS:
Changes in severe thunderstorm environment frequency during the 21st century caused by anthropogenically enhanced global radiative forcing
Robert J. Trapp , Noah S. Diffenbaugh, Harold E. Brooks, Michael E. Baldwin, Eric D. Robinson , and Jeremy S. Pal
Severe thunderstorms comprise an extreme class of deep convective clouds and produce high-impact weather such as destructive surface winds, hail, and tornadoes. This study addresses the question of how severe thunderstorm frequency in the United States might change because of enhanced global radiative forcing associated with elevated greenhouse gas concentrations. We use global climate models and a high-resolution regional climate model to examine the larger-scale (or “environmental”) meteorological conditions that foster severe thunderstorm formation. Across this model suite, we find a net increase during the late 21st century in the number of days in which these severe thunderstorm environmental conditions (NDSEV) occur. Attributed primarily to increases in atmospheric water vapor within the planetary boundary layer, the largest increases in NDSEV are shown during the summer season, in proximity to the Gulf of Mexico and Atlantic coastal regions. For example, this analysis suggests a future increase in NDSEV of 100% or more in locations such as Atlanta, GA, and New York, NY. Any direct application of these results to the frequency of actual storms also must consider the storm initiation.
Full PDF here
I find this most interesting:
Attributed primarily to increases in atmospheric water vapor within the planetary boundary layer, the largest increases in NDSEV are shown during the summer season, in proximity to the Gulf of Mexico and Atlantic coastal regions. For example, this analysis suggests a future increase in NDSEV of 100% or more in locations such as Atlanta, GA, and New York, NY. Any direct application of these results to the frequency of actual storms also must consider the storm initiation.
Yes, you must consider the storm initiation. The one thing the Tel Aviv researchers apparently have not taken into account in their GCM’s is urban evapotranspiration increases (due to irrigation), aerosols (dust and other cloud seeding nuclei from the urban area) and the role of UHI and boundary layer surface roughness in helping thunderstorm formation. Such factors have been shown to be a powerful convection assistant:
Urban Aerosol Impacts on Downwind Convective Storms
Susan C. van den Heever and William R. Cotton (2007 BAMS)
The impacts of urban-enhanced aerosol concentrations on convective storm development and precipitation over and downwind of St. Louis, Missouri, are investigated. This is achieved through the use of a cloud-resolving mesoscale model, in which sophisticated land use processes and aerosol microphysics are both incorporated. The results indicate that urban-forced convergence downwind of the city, rather than the presence of greater aerosol concentrations, determines whether storms actually develop in the downwind region. Once convection is initiated, urban-enhanced aerosols can exert a significant effect on the dynamics, microphysics, and precipitation produced by these storms. The model results indicate, however, that the response to urban-enhanced aerosol depends on the background concentrations of aerosols; a weaker response occurs with increasing background aerosol concentrations. The effects of aerosols influence the rate and amount of liquid water and ice produced within these storms, the accumulated surface precipitation, the strength and timing of the updrafts and downdrafts, the longevity of the updrafts, and the strength and influence of the cold pool. Complex, nonlinear relationships and feedbacks between the microphysics and storm dynamics exist, making it difficult to make definitive statements about the effects of urban-enhanced aerosols on downwind precipitation and convection. Because the impacts of urban aerosol on downwind storms decrease with increasing background aerosol concentrations, generalization of these results depends on the unique character of background aerosol for each urban area. For urban centers in coastal areas where background aerosol concentrations may be very low, it is speculated that urban aerosol can have very large influences on convective storm dynamics, microphysics, and precipitation.
and this one:
Simulation of St. Louis, Missouri, Land Use Impacts on Thunderstorms
Christopher M. Rozoff, William R. Cotton, and Jimmy O. Adegoke (JAM 2003)
A storm-resolving version of the Regional Atmospheric Modeling System is executed over St. Louis, Missouri, on 8 June 1999, along with sophisticated boundary conditions, to simulate the urban atmosphere and its role in deep, moist convection. In particular, surface-driven low-level convergence mechanisms are investigated. Sensitivity experiments show that the urban heat island (UHI) plays the largest role in initiating deep, moist convection downwind of the city. Surface convergence is enhanced on the leeward side of the city. Increased momentum drag over the city induces convergence on the windward side of the city, but this convergence is not strong enough to initiate storms. The nonlinear interaction of urban momentum drag and the UHI causes downwind convection to erupt later, because momentum drag over the city regulates the strength of the UHI. In all simulations including a UHI, precipitation totals are enhanced downwind of St. Louis. Topography around St. Louis also affects storm development. There is a large sensitivity of simulated urban-enhanced convection to the details of the urban surface model.
In 2000, Qing Lu Lin and Robert Bornstein, from San Jose State University, used data from meteorological stations set up during the 1996 Summer Olympics and discovered that the urban heat island in Atlanta created frequent thunderstorms. Using the National Weather Service’s newly installed local mesonet to collect data (setup for the purpose of aiding weather forecasts for Olympic athletic events), Lin and Bornstein found that five of nine days of precipitation over Atlanta were caused by the urban heat island effect.
Urban heat islands and summertime convective thunderstorms
in Atlanta: three case studies Lin and Bornstein 2000 (PDF)
Data from both 27 sites in the Atlanta mesonet surface meteorological network and eight National Weather Service sites were analyzed for the period from 26 July to 3 August 1996. Analysis of the six precipitation events over the city during the period (each on a di!erent day) showed that its urban heat island (UHI) induced a convergence zone that initiated three of the storms at di!erent times of the day, i.e., 0630, 0845, and 1445 EDT. Previous analysis has shown that New York City (NYC) e!ects summer daytime thunderstorm formation and/or movement. That study found that during nearly calm regional flow conditions, the NYC UHI initiates convective activity. Moving thunderstorms, however, tended to bifurcate and to move around the city, due to its building barrier e!ect. The current Atlanta results thus agree with the NYC results with respect to thunderstorm initiation.
And then there’s this one: (from planning.org)
The urban heat island effect causes the warmer air (including its higher concentrations of moisture and pollutants) to rise more readily than cooler air over non-urban areas (Oke 1987). Consequently, moisture and pollutants are transported into higher levels of the urban atmosphere. Thus, the urban heat island creates a warmer, moister atmosphere over the city. Once lifted, the air will cool and, if enough moisture is available, clouds and precipitation may form.The increased number of cloud condensation nuclei (CCN) and ice forming nuclei (IN) from urban pollution further enhances urban precipitation.
See: http://www.atmosphere.mpg.de/enid/3rm.html and watch the animations.
It seems to me that local boundary layer conditions have a far greater impact on thunderstorms than a 0.8C per century background warming signal. Further, as cities tend to increase their area, the local effects on thunderstorm formation are likely to increase.
For example, this recent story thanks to Dr. Roger Pielke Sr.
One of the points worth noting is that there were fewer than 20 cities of 1 million or more a century ago, there are 450 today.
It seems that when they ignore important and significant mesoscale urban factors like these in favor of broader GCM models, the Tel Aviv researchers have a clear case of modeled confirmation bias on their hands.
After all, thunderstorms are local events, so shouldn’t they be looking for local factors too?