World’s First Seasonal Lightning Forecast

At about 250 lightning flashes per square kilometer per year, the Lake Maracaibo Basin in northwestern Venezuela has the highest annual lightning rate of any place in the world.

Lightning activity is so common there that it has a proper name, Catatumbo Lightning, named for the Catatumbo region located in the southwest corner of the basin. A person is three times more likely to be struck by lightning in Catatumbo than in the entire continental United States.

Besides the implications for human safety and well-being, lightning strikes also kill or maim cattle and other livestock in the region, and can frequently interrupt oil and natural gas exploration in a country that holds the world’s largest proven oil reserves.

In January  this year, a team of researchers led by Ángel Muñoz published a seasonal lightning forecast for Catatumbo — the first of its kind for the region and for the globe. The team recently won the ‘Orden de la Zulianidad’, an award given by the state government of Zulia in Venezuela for outstanding contributions to society.

Muñoz, who is now a postdoctoral research affiliate at Princeton’s Atmospheric and Ocean Sciences program, explains the research and its applications in a detailed interview below.

What makes Catatumbo such a flashpoint for lightning?

Warm and moist low-level winds coming from the Caribbean Sea, and the presence of the Andes and the Perijá mountain ranges surrounding Lake Maracaibo, produce ideal conditions for thunderstorms, especially in the southwestern corner of the lake basin. The tall mountains can lead to the development and persistence of clouds with large vertical profiles when sustained winds bring moisture to the area. This is important because lightning frequency increases very rapidly with cloud height.

Incidentally, we’ve helped corroborate that there is not one, but two lightning hotspots in the southwestern quadrant of the basin: one close to the mouth of the Catatumbo River and another at the border between Venezuela and Colombia.

What are the main variables that you used to make the lightning predictions?

Our team explored the role of many physical variables, including sea-surface temperatures, winds, moisture transport and convective available potential energy (a.k.a. CAPE, a measure of the potential for storminess in a region). We did this in both the observational data and our own high-resolution, numerical simulations. We found that CAPE and winds had the most direct influence on lightning in Catatumbo, so we developed an index from these two climate variables to use as a basis of our prediction model. We’re not ignoring the other climate variables, however. Ultimately, since they all have an impact on CAPE and winds, our index captures variability from many climate processes. This is why the lightning forecasts we developed for the region base on this index had high skill, about twice the typical skill for rainfall forecasts there.

We made extensive use of both IRI’s Climate Predictability Tool and its Data Library in our research and analysis.

Do other climate timescales play a role? What causes lightning rates in the region to fluctuate?

Our research identified the role of what we’re calling the Maracaibo Basin Low-Level Jet — an ebbing and flowing ‘tide’ of winds present between the ground and the base of the clouds that blow from the Caribbean to the southern part of the basin, and then in the opposite direction— as the main regulator of lightning activity at daily scale. The interaction of these winds with the mountain range surrounding the basin explains the location, timing and high frequency of events. The intensity and moisture transported by this low-level jet change along the year, depending on the influence of seasonal-scale climate drivers such as the El Niño-Southern Oscillation, the Caribbean Low-Level Jet and the Atlantic Meridional Mode.

The dangers that lightning pose are so localized. Why is a seasonal lightning forecast over an area as large as Catatumbo useful?

Lightning is arguably the most dangerous natural hazard, due to its unpredictability and the frequency of strikes. A recent review of annual fatalities in 23 countries cites deaths rates ranging from 1 to 84 per million people. Overall, developing countries show higher lightning-related death rates than developed countries, especially in cases where a large percentage of the population is found in rural areas.

Developed countries are vulnerable when lightning occurs in areas with a high concentration of expensive infrastructure. In the U.S., for example, lightning is estimated to account for $8-10 billion in losses to the U.S. economy each year.

The Lake Maracaibo Basin has characteristics of both developing and developed countries. There’s a rural population of farmers and fishermen with mostly no protection from extreme weather. There’s also very expensive infrastructure, including approximately 13,000 oil wells that produce 1.95 million barrels a year of crude oil, or about 50% of Venezuela’s export capacity. In addition, lightning in the lake basin is also responsible for $400,000 in average losses per electric power plant every year.

Improving our ability to predict lightning activity in the region would spare Venezuela some of these losses. The work also has potential application in neighboring Colombia, with shares similar statistics.

The sensor you built for this work also has an interesting backstory – can you tell us about it?

The Center for Scientific Modeling in Venezuela designed and built the set of microsensors we’re using in our Catatumbo expeditions. We launched these iCaro sensors, as they’re called, using tethered balloons. The sensors help us characterize the evolution of the planetary boundary layer, which is the the part of the atmosphere between the ground and the base of the clouds, and study conditions conducive to lightning. Since April 2015, we have had five field campaigns occurring about every 3 months. We acquire data every 30 minutes continuously for 2-3 days. We also use the data to calibrate our prediction models.

What’s next in this research?

We are designing a lightning early warning system named SIVIGILA for the Lake Maracaibo Basin. This involves real-time monitoring using a new network of detectors, short-term forecasts using a calibrated high-resolution model and the seasonal forecasts using the models we previously reported on. Our team is following IRI’s ‘ready-set-go’ approach in which action-oriented information at multiple timescales is provided to the user to facilitate decisions.

We are still looking for funding to continue the field campaigns that will keep the models calibrated, and to buy and maintain the lightning detectors.

For more information

http://cmc.org.ve/Catatumbo
http://cmc.org.ve/ExpedicionesCatatumbo