Jay Grymes and David Greenland
Katrina and Rita – names that will live forever – remain a part of the South Louisiana dialog and a pair of storms that will undoubtedly reshape the way Louisiana residents think about tropical weather. Virtually every aspect of community and business life across the Bayou State continues to display a direct effect from these catastrophes, and their signatures of destruction remain plainly evident in the agriculture and forestry sectors as well. Agricultural losses attributed to the 2005 tropical season are still being assessed, and LSU AgCenter estimates put the figure at well over $1.5 billion. And those losses have been compounded further by a year-long drought across much of the state.
Katrina and Rita highlight an active run of hurricane seasons for Louisiana, with 11 tropical cyclones impacting the state in just the last five years. Among these, a sometimes-forgotten Hurricane Cindy preceded Katrina and Rita in the 2005 season. The 2002 hurricane season saw a record four storms strike the Louisiana coast. And 2001’s Allison proved to be among the greatest flood-makers in recorded history for some southern parishes. With this recent flurry of tropical activity, the question on the minds of many is: Are these kinds of extreme weather events becoming the new norm for Louisiana? If so, is there anything we can do to mitigate the effects?
We must remember that the climate is constantly changing. A number of hurricane seasons have come and gone without a single storm threatening our state. Yet years with multiple landfalls are not uncommon. Over the past century, Louisiana has suffered immeasurable losses from other memorable hurricanes like Audrey, Betsy, Camille and Andrew. But the flurry of tropical activity in recent years somehow seems different.
If we examine Louisiana landfalls from August to October over the past 200 years, for example, we can discount any obvious long-term trends (Figure 1). But the last five years have been extra busy for the Louisiana coastal zone (Figure 2).
Increased Hurricane Activity
It is clear that hurricane activity in the Atlantic Basin is way up in recent years. Ten of the past 11 years have seen storm counts rise above the 100-year average. Major hurricane (Category 3 or stronger) numbers appear to be on the rise. And the 2005 season was the first on record with four confirmed Category 5 storms: Emily, Katrina, Rita and Wilma (three were Gulf of Mexico storms). Indeed, the hyper-active 2005 Atlantic hurricane season – with 28 tropical systems – required hurricane forecasters to use the Greek alphabet for storm names for the first time ever.
Without doubt, the loss of life associated with Katrina stands out as the most devastating in recent memory. But also noteworthy are the eye-opening economics associated with recent tropical weather. Preliminary data suggest that seven of the 10 most costly U.S. hurricanes occurred during the 2004 and 2005 seasons.
Scientists are searching for explanations for the apparent changing frequencies in the Atlantic tropical weather. But such investigations are complicated by improved observation and reporting practices over the past 150 years. These new methods include aircraft reconnaissance, which began in the late 1940s, and satellite technology.
For example, there are suggestions of a cycle in Atlantic hurricane activity – a periodic flip-flop between prolonged periods of increased activity to little activity and then back to higher tropical cyclone counts. The cycle, which takes about 50 to 70 years, is thought to correspond with changes in Atlantic Ocean temperatures. But the reliable time series of Atlantic storms only extends back 100 to 150 years, and statisticians warn that a longer period of data is needed to confidently declare the cyclic-activity hypothesis as valid.
Then, too, is the issue of this potential cyclic activity and what it means in terms of landfall frequencies. Recent work at LSU shows little in the way of a compelling association between U.S. landfalls and this proposed hurricane cycle. If a strong relationship does exist, investigations by state climatologist Barry Keim and colleagues indicate that the linkage is most likely along the Florida and Carolina coasts.
Louisiana Hurricane History
Although records of early Louisiana hurricanes are limited, some aspects of Louisiana hurricane history are worth mentioning. For example, the first notation of tropical weather affecting Louisiana dates back almost 500 years. In 1527, while exploring along the central Gulf Coast, Panifo de Narvaez of Spain reported that his fleet was caught in a violent storm off the mouth of the Mississippi, and ships were lost. Over the next centuries, reports of tropical weather can be found throughout diaries and letters and from the logs of those that established the first settlements in and around New Orleans.
1860 was a noteworthy year for South Louisiana agriculture. A mid-August storm made landfall in southeastern Louisiana and ruined sugarcane, rice and corn crops. A month later, a mid-September storm made landfall at the mouth of the Mississippi, followed by an early October storm passing over New Orleans and Baton Rouge and adding to the losses. The 1860 triple-strike proved a devastating blow to the sugarcane industry that year.
The threat of annual tropical storms remains part of life for the Bayou State. And recently, an apparent increase in major storm frequency has been linked by some researchers as a result of continued global warming. So what does all this mean for Louisiana and its agriculture and forestry sectors? Obviously, a debate on the role of global warming on hurricane activity – and indeed, the debate on the global warming issue in general – is sure to continue. And don’t look for a consensus from climatologists any time soon.
Still, Louisiana communities and industries need to critically evaluate the effects of the recent decade of tropical weather and examine opportunities to implement strategies to mitigate at least some of the destruction. Whether the recent run of elevated hurricane activity reflects the onset of a multi-decade run of increased storm threats or whether this is simply an unusual and unexpected short-term trend, Louisiana will always be a frequent landfall target.
More needs to be done to analyze the effects of hurricanes on specific Louisiana crops and agricultural commodities. This is not an easy task because of changing agricultural practices and differing crop varieties. Furthermore, different crops are affected differently.
Take sugarcane, for example. Be tween 1963 and 2002, the mean statewide yield for the period was 27.2 tons per acre. However, yield was reduced by an average of 1.1 tons per acre during years when hurricanes passed over the state in late summer and fall. Some might consider that a relatively small reduction given the potential damage that hurricanes can inflict, particularly at or near harvest time. We hypothesize that the reason the apparent hurricane effect is not greater is that it is rare for a hurricane to affect the entire southern part of the state. Even in those years where Louisiana has suffered multiple hits, the geographic effects were somewhat contained.
Another lesson can be learned from the 2005 storm catastrophes. Each of the two storms was a record-setter in its own right, and the occurrence of intense storms like Katrina in the southeast and Rita in the southwest within a one-month period was unprecedented. Yet their effects on South Louisiana mainstay crops were not as devastating as they might have been had they each arrived at different times of the season. With Katrina’s August landfall, much of the southeast and south central Louisiana sugarcane crop was able to recover before the peak harvest period. And one month later, the effect of Rita on the 2005 southwestern Louisiana rice crop was lessened by the fact that the storm occurred after the main crop had been harvested.
Such assessments are only the starting point for detailed, comprehensive studies of the large-scale, long-term implications of tropical weather on Louisiana agriculture, but they demonstrate that there is some potential for fruitful studies. And given the ever-increasing complexity of the international marketplace and Louisiana’s niche in world agribusiness, we believe it is vital that firmer understandings be pursued with regard to the relationships between Louisiana agriculture and forestry and future tropical threats.
A new norm? The jury’s still out. Perhaps the answer is not all that important. Whether we are experiencing a new climate regime or simply a temporary run of enhanced tropical activity, we should position ourselves to take advantage of the research opportunities available. In that way, Louisiana agriculture can be better prepared to deal with our ever-changing climate.
(This article was published in the summer 2006 issue of Louisiana Agriculture.)