Home | Risk Defined | News & Views | Credentials


specific weather and climate threats

There are few, if any, places on Earth where dangers from weather are totally absent. Weather and climate risks come in three varieties: risks that can kill you, risks that can cost you money, and risks that merely inconvenience you. Of course, these categories are not mutually exclusive. Getting killed may be the ultimate inconvenience.

Weather Risks - Weather risks are just what one would think, dangerous weather events that can cause death, destruction, or at least significant inconvenience.

Tornadoes - The high winds of tornadoes turn debris into deadly missiles, knock down structures onto occupants, and toss around vehicles and the occupants within. While most years not causing the most fatalities among types of dangerous weather, the capricious and random nature of tornadoes, coupled with the difficulty of forecasting them with precision, make tornadoes justly feared, especially in the Tornado Alley of the United States.

Hurricanes - The combination of high winds, sometimes augmented by associated tornadoes, and flooding from storm surge and heavy rain, plus the large areas affected, make hurricanes a deadly threat and capable of causing some of the costliest damage of any weather disaster.

Thunderstorms - While many thunderstorms just provide a natural fireworks show, they all have the potential to produce dangerous weather phenomena. Thunder isnít dangerous, but thunder is a byproduct of lightning which is a deadly threat. Thunderstorms can also produce high winds capable of knocking down large limbs and entire trees which have caused fatal injuries. A third threat from thunderstorms is extremely heavy rain which can cause flash floods. Occasionally thunderstorms produce hail which can cause severe damage, in generally small areas for any individual event, to crops and natural plants as well as human artifacts like automobiles and windows. Large hail can cause injury and even death to humans, but this is rare.

Floods - Floods come in two broad types, characterized by the speed of their onset. Floods which affect large areas are typically slow to develop and slow to recede, taking days, weeks, or in extreme cases months, for each phase. Some of these can be considered climate risk events. The flooding in the Midwest U.S. during 1993 is a classic example of flooding that was a direct result of short term climate anomalies. On the other hand, flash floods, as the name implies, develop rapidly and this makes encountering them often unexpected and thus especially dangerous. While people are killed by slowly developing floods, it is less common because the flooding does not, or at least should not, take people by surprise. However, the larger area which this type of flood generally affects means that more property damage tends to occur. Flash floods catch people off-guard, sometimes asleep, and can imperil lives before the victims realize the danger. Hurricanes can cause flooding from heavy rain and storm surge, and a significant amount of the death and damage from hurricanes are from flooding instead of wind.

Winter storms - In winter storms snow and/or ice create dangerous driving, and sometimes walking, conditions. If the travel conditions prevent someone from completing their journey, the cold, possibly made more dangerous by high winds, creates life threatening hypothermia if adequate shelter is not available.

Heat waves - Periods of high temperatures stretching over multiple days, especially coupled with high humidity and high overnight minimum temperatures, cause physiological stress on the human body which can prove fatal, especially among vulnerable groups like the elderly. Spending adequate time in air conditioned conditions provides an obvious and effective defense against the danger of heat waves, but many people have no or limited access to such cooled spaces. For those who must be exposed to high temperatures, keeping adequately hydrated by drinking water is vital.

Avalanches - An avalanche is a rapid flow of snow down a slope. In some areas of the Earth, avalanches are a significant threat to people and infrastructure. In the United States the risks from avalanches is mainly to back country recreationists like skiers and snowmobilers who venture away from the maintained areas. However, there are towns in the U.S. which are located in known avalanche zones. Like most areas of weather forecasting, the science of understanding and predicting avalanche risk has advanced in the past several decades, but the lack of direct observations of snow conditions over vast mountain areas of the U.S. inhibits the creation of accurate avalanche forecasts for many areas. Fortunately these areas tend to be sparsely populated or visited. In Switzerland, a smaller area where more of the population lives in the mountains, a denser observation network, specifically directed toward avalanche prediction has proven effective.

Landslides - The threat from landslides is somewhat similar to that of avalanches except that instead of tons of snow sliding downhill, tons of mud, dirt, rock, and whatever was on or in the dirt slides downhill. Landslides (or rockslides) can occur whenever the structural strength of a layer of the ground is exceeded by the force of gravity pulling the ground downhill. Landslides and rockslides can occur at any time due to the accumulation of weathering effects, but often landslides occur because of heavy rain soaking steep hillsides until a layer of soil is virtually "floated" free and slides onto lower, ultimately flatter, terrain. In the United States there are significant concentrations of people and associated infrastructure in areas that are in danger of landslides. California is one of these areas due to its denser population living in hilly terrain and often intense winter rain storms, sometimes coupled with hillsides denuded of vegetation due to wildfires.

Climate Risks - Climate is the long term average of weather parameters such as temperature and rainfall. Typically the time period over which these averages are calculated is 30 years. Climate anomalies, which are difference between the 30 year averages and averages over shorter time periods, can be the source of climate hazards. These differ from weather hazards by being caused by prolonged periods of weather that tends to be, for instance, hotter than normal or drier than normal, while weather hazards are usually caused by distinct events like individual storms. However, the line dividing climate and weather risks can be fuzzy. Some weather risks above straddle the border with climate risks. For instance, a flood may be due to a prolonged period of above normal precipitation rather than one cloudburst. A heat wave is more than a single really hot day, yet a warmer than normal summer may not encompass an actual heat wave.

Drought - Drought is a prolonged period of generally below normal precipitation, sufficiently so that the lack of water produces detrimental consequences. The effects may be observed in natural ecosystems, human society, or both. Drought can wilt or kill plants, decrease crop yields, kill wild and domestic animals, strain water supplies for people, decrease hydropower production, even restrict transportation. The effects of drought are especially dire in poor, semi-arid regions with severely limited water resources to begin with and little infrastructure or money to cope with food and water shortages. As the impacts have become more prominent, drought is being monitored more closely in the United States in recent years. National Drought Monitor

Floods - As mentioned above, some floods can be classified as climate risks. These floods are in a sense the flip side of drought, which is to say significantly more precipitation than normal over a period of time. Some river basins experience floods almost every spring as snow melts. Other river basins experience floods due to yearly monsoon rains. Since these events are typical of the annual climate cycle, they can be considered climatic floods. However, these floods can be exacerbated by unusually heavy snowpack or heavier than normal monsoons. A prolonged period of warmer than normal, above freezing temperatures and/or unusually heavy rain on top of snow cover can also exacerbate flooding from snowmelt.

Even some flash floods which are triggered by weather events are partially climate events. If there has been enough precipitation, perhaps over an extended period of time, that the ground is saturated, it can take a smaller rainfall event than usual to cause a flash flood because the rain all runs off into the streams rather than partly soaking into the ground.

Wildfire - Wildfires are fires in natural areas such as forests or grasslands as opposed to manmade structures. Of course, wildfires can spread to manmade structures that are in or near natural areas, and this is increasingly a risk. Drought is often an antecedent of wildfire, but not always. Certain landscapes are regularly visited by wildfire under normal climatic conditions. Such wildfires are often part of an annual cycle in regions which experience alternating wet and dry seasons, such as Southern California. In the eastern U.S. autumn can be a period of enhanced wildfire risk because the deciduous trees are losing their leaves and sap and the weather tends to have long periods of little rain plus low humidity. However, wildfire frequency and intensity in such regions can be made worse by drought.

Climate change - The climate, as defined by time averages of weather phenomena, is always changing. Sometimes these changes are indistinguishable from the fluctuations due to the limited sample size of even 30 years of weather observations. Sometimes the changes are far enough outside the likely range of such statistical uncertainty that they represent genuine differences in the climate from one period to another. The possible causes of these changes are numerous, but due to the complex nature of the climate system and our still limited knowledge, it is difficult to apportion a given change among specific causes. Whatever the causes, the fact that natural and manmade systems are structured to deal with the range of weather associated with a certain climate means that climate change can damage these systems.


Home | Risk Defined | News & Views | Credentials


 

©2012 Russell Martin