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Climate and Weather: Information and Education

Climate Patterns in SE USA

We all know that southeast USA is a region within Unites States which is more prone to seasonal and interannual climate variability. It faces the sea by its wide coastline areas thus it is exposed to stronger effect from hurricanes and severe thunderstorms as well as some of the major natural hazards such as inland floods, tornadoes, drought and heat. These impacts of climate variability are not only related to human health and economy but also the agricultural systems. The past trends of temperature, precipitation and hazardous events (especially hurricanes and tornadoes) in SE USA region are explained in detail below:

 

Temperature

There was no significant increase in temperature in southeast since 1970 (Figure 1). The studies on predictions reveal that there may be 4.5° to 9°F of possible rise in summer temperature by the end of this century (Karl et al., 2009). Based on a study related to 20-years temperature anomaly using multi-model predictions, it was found that temperature anomaly may be higher in southern part SE USA and Florida than the northern part of SE USA during winter months (Stefanova et al., 2012). The number of freezing days has been increased in the northern part than southern part of SE USA (Figure 2).

Figure 1
Figure 1. Number of days per year with peak temperature over 90°F (Source: Karl et al., 2009)

Figure 2
Figure 2. Change in freezing days per year (during 1976 to 2007) (Source: Karl et al., 2009)

 

Precipitation

Average precipitation in all over southeast shows increase in fall precipitation by 30% but decrease in summer/spring precipitation by nearly 10%. However, precipitation in south Florida decreased by 10% in all of the seasons.

Figure 3
Figure 3. Observed changes in Precipitation in southeast USA (Source: Karl et al., 2009)

Though the predictions by different climate models regarding precipitation in future is not that reliable, there are some interesting facts related to climate pattern of southeast USA. The overall predicted results tell about decrease in rainfall and drier southern regions specially Florida, Alabama and Georgia in future. There may be increase in precipitation during spring but decrease during summer which relates to more floods during spring and drought during summer in future (Wilbanks et al., 2010). The study of Stefanova et al. (2012) also depicts that the precipitation anomaly may be higher in southern AL, GA, most of the southeast part of NC and SC and almost entire FL than northern AL, GA, NC and northwest SC during December-January-February.

More information on Big Rain Events (>2" rainfall in two-day period)
http://climatecenter.fsu.edu/climate-data-access-tools/big-rain

 

Hazardous Events

We all have noticed that the intensity and number of hurricanes have already increased since last couple of years. The sea level rise along with increase in sea surface temperature is more likely to increase the intensity of strongest hurricanes in future.

Hurricanes

El Niño, the warm phase of ENSO decreases the vertical wind shear over Atlantic basin which help form hurricanes phase. On the other hand during the cold phase of ENSO (La Niña), the vertical wind shear over Atlantic basis increases and that increases the chance of hurricanes. A recent study manifested clear differences in numbers of hurricane landfalls during the cold phase than the neutral and warm phase of ENSO. The study (Co-authored Dr. Jim O'Brien from Florida State University) showed increased number of hurricanes during La Niña than El Niño and Neutral in Georgia to Maine however the risks of hurricanes were more during both La Niña and Neutral phases of ENSO than El Niño in Florida (Figure 4).

Figure 4
Figure 4. Variations in Number of Hurricane Landfalls in Warm (El Niño), cold (La Niña) and Neutral phase ENSO
(source: http://www.agroclimate.org/forecasts/hurricane_forecast.php)

For more information on Trends of Hurricane Activity click http://climatecenter.fsu.edu/topics/tropical-weather/regional-effects-of-enso-on-us-hurricane-landfalls

Tornadoes

The increase in sea surface temperature will also result in more rain and storm surges in southeast USA in near future. Although there is no clear prediction on changes in frequencies of tornadoes; the number of days that are associated with thunderstorm could increase (Karl et al., 2009; Trapp et al., 2007).

Read more on Tornadoes of Alabama at http://www.sercc.com/education_files/tornadoes_al.pdf

 

 

References

Karl, T.R., J.M. Melillo, and T.C. Peterson (eds.). 2009. Global Climate Change Impacts in the United States. Cambridge University Press, New York.

Stefanova, L., Misra V., O'Brien, J.J., Chassignet, E.P. and Hameed S. (2012). Hindcast skill and predictability for precipitation and two-meter air temperature anomalies in global circulation models over the Southeast United States. Clim Dyn, 38: 161-173.

Trapp, R.J., N.S. Diffenbaugh, H.E. Brooks, M.E. Baldwin, E.D. Robinson, and J.S. Pal. 2007. Changes in severe thunderstorm environment frequency during the 21st century caused by anthropogenically enhanced global radiative forcing. Proceedings of the National Academy of Sciences 104(50):19719–19723.

Wilbanks, T., Ebi, K., Hoogenboom, G. and Kirshen, P. (2010). Climate Change Impacts in the Southeastern United States- Draft Discussion Paper.