Dry Lightning as a Forest Predator: A Review

Shelly Rajput

Department of Applied Sciences, Delhi Global Institute of Technology, Haryana, India.

*Corresponding Author E-mail: shelly.rajput@rediffmail.com

ABSTRACT:

Lightning discharges have great impact on forest ecology. There are many indications that lightning is main cause for wildfires. Dry lightning or rain free lightning strikes are prominent natural source for wildfires. In remote areas dry lightning can escalate into uncontrollable events. Dry lightning often ignites wildfires in dry vegetation areas. It has been studied by several researchers that dry lightning strikes are most destructive and costly wildfires. The present work is the review study of impact of dry lightning on wildfires. The influences of variables such as environment, weather, fuel dryness and geographical factors and their effect on dry lightning are also aimed to study. Dry lightning has been shown to be the cause of huge wildfires, and it is well known that wildfires are a growing threat as climate continues to warm. So, an understanding of dry lightning is essential to fire management.

KEYWORDS: Dry lightning, Wildfires, Environment.

INTRODUCTION:

Dry lightning occurrence is of critical importance to land management agencies since this type is most likely to cause wild land fires. Dry lightning strikes often ignite wildfires in dry vegetation, especially in remote areas. These strikes can quickly grow out of control under favorable conditions, causing damage and burning large areas. It has been observed, that dry lightning and dry thunderstorms cause the majority of wildfires in western U.S.

Dry lightning is cloud to ground lightning without any accompanied rainfall nearby. Dry thunderstorm are thunder and lightning that occur without bringing rain to the ground, it occurs when most or all of its precipitation evaporates before reaching the ground. Lightning strikes that occur with minimal rainfall (about with less than 2.5mm of rainfall) are known as dry lightning. In normal thunderstorm, lightning strikes, while rainfalls from the storm clouds usually accompanied by the sound of thunder. When the lightning hits the ground, it may cause a spark of flame, but the rain which comes down along the lightning puts the fire out before it has chance to spread. In dry storm rain is produced but it never reaches the ground. That’s called Virga. These dry storms tend to form extremely high, which mean that the rain may pass through a huge zone of warm air, this dry warm air cause the rain to evaporate. The dry thunderstorms are accompanied by dry microbursts, gusts of cold air which rush down from clouds and spread rapidly when they hit the ground causing gusty winds that can fan flames at the surface of earth. Komarek (1964); Pyne et al. (1996); Soler et al. (2021) explained that the dry lightning strikes are natural ignition source for wild land fires. Bates et al. (2018) found in their research that dry lightning spread in large areas as compared to fires initiated by environment ignition source. Flannigan and Wotton (1991) studied that dry lightning strikes creates challenges to fire management agencies in remote areas and develop into significant wild fire events.

Dry lightning can be disastrous even when conditions are not so dry. A Washington State University led study of lightning- ignited wildfires in the U.S. west, found the lightning strikes can cause wildfires even up to 7.7mm of precipitation. While a low amount of rain, the more accurate estimation could help to detect fires earlier, especially “holdovers fires” which can flicker for many days before exploding into full-blown wildfires. “Holdover fires “or “Sleepers “tended to occur with even higher precipitation of about 3mm to 7.7mm. Kalashnikov a Ph.D. candidate in the WSU School of the Environment in her study observed, that the dry lightning can start wild fires in remote areas that are hard for fire fighters to reach and “holdover fires” create an additional problem because they are so hard to detect in early stage. Kalashnikov in her study explained that “holdover fires” can spread fire in a day or two or sometimes it may take a week or more until condition are favorable. Forest areas are most effected by such fires as the lightning might ignite the leaves and twigs on forest floor, which is unreachable from rain as well as view because it is covered by the dense branches.

FACTORS INFLUENCING DRY LIGHTNING:

Several investigators in their study found that environmental, weather conditions, solar radiations and atmospheric instability influence the dry lightning strikes. Bradshaw et al. (1983) explained that the occurrence and spread of wildfires depends on the availability of dry fuel, ignition and wind. Nash and Johnson (1996); Renkin and Despain (1992) observed that the lightning strikes igniting fires are influenced from fuel load, fuel moisture and rainfall conditions during lightning discharges.

Solar radiation was found to be a prime predicator of dry lightning strikes, reflecting its effect on weather conditions that favor fuel dryness and therefore increase chances of lightning fires. Byram (1943); Liu et al. (2014) suggested that higher solar radiation levels, accelerates fuel drying and reduce fuel moisture content which effect the lightning fire chances to spread. Amila et al. (2024) observed that in Tasmania, lightning fires are more influenced by fuel dryness. Also, they integrated dry lightning conditions and trained their models for Tasmania’s FFDI (Forest Fire Danger Index) and found the improvement in comparison with existing model of Clarke et al. (2019) because Tasmania has higher rainfall and lower FFDI than Victoria. Their model was developed based on the Clarke et al. (2019) model, for Victoria and tested in Tasmania, found that there is a positive relationship between FFDI and lightning fire. Almia et al. (2024) suggested machine learning techniques to identify areas prone to lightning fire. Also observed that how fuel characteristics and moisture content influence fire initiation. Rorig and Ferguson (1999), in dry lightning research observed that atmospheric stability and moisture can predict dry lightning in advance.

Treeless fuel types such as grasslands, sedgelands and alpine heathlands are more influenced with lightning fires, whereas eucalypt forest and rain forest are less influenced. As in treeless area there are inadequate canopy cover, surface fuels like grasses, shrubs, and herbs are directly exposed to sunlight leading to higher temperature and reduce moisture. It has been studied those open forests are more susceptible to lightning fires due to their direct exposure to solar radiations and regular reduction of moisture. Forest with dense canopies, may provide shading and moisture retention, and thereby reduce solar radiation penetration and air flow.

Furlaud et al. (2021); Leonard et al. (2014) explained in their work that rainforests and wet eucalypt forest are less prone to lightning fires. Colhoun and Shimeld (2012); Jones et al. (2019) also found in their study, that areas with wet eucalypt forest, woodland and rainforest have low probabilities of lightning caused ignition and region with dry eucalypt forest show a medium to high probability of ignition in central to eastern Tasmania. Several researchers in their study found that the dryness level in atmosphere is correlated well to fire occurrence. The green dryness level(moist), indicates very low or no probability of fires or significant growth on existing fires. Yellow dryness level(dry) indicates low probabilities of new large fires and brown dryness level(brown) indicates a very dry environment, which result in a higher-than-normal probability of fire growth.

Nauslar et at. (2013); Rorig et al. (2007) studies that atmospheric conditions conductive to dry lightning are a low dry layer coupled with mid-level instability. The rain that falls from higher altitude thunderstorms passes through drier lower layer evaporates before hitting the ground, preserving the dry fuel below for ignition from lightning flashes. Dry lightning provides the means of igniting dry fuel, while the convective environment conditions provide wind to aid in spreading the fire immediately after ignition. Amila et al. (2024) during their research studied, the contribution of weather conditions and associated fuel dryness to the probability of lightning ignitions. Their research provided an important baseline and geographic context for understanding how lightning fires in Tasmania will respond to climate change, knowledge essential of wildfire management strategies.

Duryer and Uman (2014); Song et al. (2024) found in their research that the existing understanding and data regarding lightning ignition process are inadequate for developing physics- based model. Statistical and data-based models offer an alternative approach for more thorough investigation into lightning fires. Machine learning techniques for studying dry lightning has found to be as a significant source for wildfires. Earth system modelling suggests that lightning activity will increase due to climate change in many regions globally.

CONCULSION:

Dry thunderstorms are the most common origin of wildfires. Dry thunderstorm generally occurs in desert or places where the lower layer of the atmosphere usually contains little water vapor. Any precipitation that falls from elevated thunderstorm can be entirely evaporated as it falls through the lower dry layers. They are commonly during the summer month across much of western North America areas. Several researchers have addressed both the environment changes and natural causes of wildfires. The growing importance of lightning fires research is required to identify and improve understanding of the key bio-physical factors in indicating fires, thereby magnifying the ability to study their impact on ecosystems. Increased lightning activity is likely to increase the risk of lightning ignited wildfires. A recent study has found dry lightning outbreaks are leading cause of some of the largest wildfire, despite this, dry lightning has remained largely understudied. Further investigation of how climatic changes are altering fire weather, atmospheric instability, fuel dryness will provide more understanding for wildfire lightning.

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Received on 02.11.2024 Revised on 25.11.2024

Accepted on 12.12.2024 Published on 16.12.2024

Available online on December 31, 2024

Research J. Engineering and Tech. 2024; 15(2):65-68.

DOI: 10.52711/2321-581X.2024.00010

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