A drought is a period of drier-than-normal conditions. A drought can last for days, months or years. Drought often has large impacts on the ecosystems and agriculture of affected regions, and causes harm to the local economy. Annual dry seasons in the tropics significantly increase the chances of a drought developing and subsequent wildfires. Periods of heat can significantly worsen drought conditions by hastening evaporation of water vapour, drying out forests and other vegetation and increasing fuel for wildfires.
Drought in Australia is defined by the Australian Bureau of Meteorology as rainfall over period greater than three-months being in the lowest decile of what has been recorded for that region in the past. This definition takes into account that drought is a relative term and rainfall deficiencies need to be compared to typical rainfall patterns including seasonal variations. Specifically, drought in Australia is defined in relation to a rainfall deficiency of pastoral leases and is determined by decile analysis applied to a certain area. Note that this definition uses rainfall only because long-term records are widely available across most of Australia. However, it does not take into account other variables that might be important for establishing surface water balance, such as evaporation and condensation.
Severe weather is any dangerous meteorological phenomenon with the potential to cause damage, serious social disruption, or loss of human life. Types of severe weather phenomena vary, depending on the latitude, altitude, topography, and atmospheric conditions. High winds, hail, excessive precipitation, and wildfires are forms and effects of severe weather, as are thunderstorms, downbursts, tornadoes, waterspouts, tropical cyclones, and extratropical cyclones. Regional and seasonal severe weather phenomena include blizzards (snowstorms), ice storms, and duststorms.
The climate of the United States varies due to changes in latitude, and a range of geographic features, including mountains and deserts. Generally, on the mainland, the climate of the U.S. becomes warmer the further south one travels, and drier the further west, until one reaches the West Coast.
Climate change in California has resulted in higher than average temperatures, leading to increased occurrences of drought and wildfires. During the next few decades in California, climate change is likely to further reduce water availability, increase wildfire risk, decrease agricultural productivity, and threaten coastal ecosystems. The state will also be impacted economically due to the rising cost of providing water to its residents along with revenue and job loss in the agricultural sector. California has taken a number of steps to mitigate impacts of climate change in the state.
The United States' contiguous western and especially southwestern region has experienced widespread drought since about year 2000. Below normal precipitation leads to drought, and is caused by an above average persistence of high pressure over the affected area. Changes in the track of extratropical cyclones, which can occur during climate cycles such as the El Niño-Southern Oscillation, or ENSO, as well as the North Atlantic Oscillation, Pacific Decadal Oscillation, and Atlantic multidecadal oscillation, modulate which areas are more prone to drought. Increased drought frequency and severity is also expected to be one of the effects of global warming.
The 1988–1990 North American drought ranks among the worst episodes of drought in the United States. This multi-year drought began in most areas in 1988 and continued into 1989 and 1990. The drought caused $60 billion in damage in United States dollars, adjusting for inflation. The drought occasioned some of the worst blowing-dust events since 1977 or the 1930s in many locations in the Midwestern United States, including a protracted dust storm, which closed schools in South Dakota in late February 1988. During the spring, several weather stations set records for the lowest monthly total precipitation and the longest interval between measurable precipitation, for example, 55 days in a row without precipitation in Milwaukee. During the summer, two record-setting heatwaves developed, similar to those of 1934 and 1936. The concurrent heat waves killed 4,800 to 17,000 people in the United States. During the summer of 1988, the drought led to many wildfires in forested western North America, including the Yellowstone fires of 1988.
Droughts are a relatively common feature of the weather in the United Kingdom, with one around every 5–10 years on average. These droughts are usually during the summer, when a blocking high causes hot, dry weather for an extended period. However this means that droughts can vary in their characteristics. All types of drought cause issues across all sectors, with impacts extending to the ecosystem, agriculture and the economy of the whole country in severe cases of drought. The south east of the country usually suffers most, as it has the highest population and the lowest average precipitation per year, which is even lower in a drought. Even in these areas in severe droughts, the definition, impacts, effects and management are all minimal in comparison to drought prone areas such as Australia and parts of the United States. In recent years however, the summers of 2007, 2008, 2009, August 2010 and 2012 were wetter than normal, 2007 being wettest on record. Droughts have continued to occur in recent times, with spring 2011, July 2013, summer 2018, spring 2020, spring and summer 2022 and May and June 2023 all featuring excessively dry periods for part or all of the UK, and will likely become more severe due to climate change over the 21st century.
The 2000s drought in Australia, also known as the millennium drought is said by some to be the worst drought recorded since European settlement.
The 2010–2013 Southern United States and Mexico drought was a severe to extreme drought that plagued the Southern United States, including parts of Texas, Louisiana, Arkansas, Mississippi, Alabama, Georgia, South Carolina, North Carolina, Florida, and Oklahoma; the Southwestern States, including Kansas, Colorado, New Mexico, and Arizona; as well as large parts of Mexico, in a three-year pattern from 2010 to 2013.
A megadrought is an exceptionally severe drought, lasting for many years and covering a wide area.
The 2012–2013 North American drought, an expansion of the 2010–2013 Southern United States drought, originated in the midst of a record-breaking heat wave. Low snowfall amounts in winter, coupled with the intense summer heat from La Niña, caused drought-like conditions to migrate northward from the southern United States, wreaking havoc on crops and water supply. The drought inflicted significant economic ramifications for the affected states. It exceeded, in many measures, the 1988–1989 North American drought, the most recent comparable drought.
The historical and ongoing droughts in California result from various complex meteorological phenomena, some of which are not fully understood by scientists.
In 2022, several areas of the world experienced heat waves. Heat waves were especially notable in East Asia, the Indian subcontinent, Australia, western Europe, the United States, and southern South America. 2022 heat waves accounted for record-breaking temperatures and, in some regions, heat-related deaths. Heat waves were worsened by the effects of climate change, and they exacerbated droughts and wildfires.
The 2022 California wildfire season was a series of wildfires throughout the U.S. state of California. By the end of the year, a total of 7,667 fires had been recorded, totaling approximately 363,939 acres across the state. Wildfires killed nine people in California in 2022, destroyed 772 structures, and damaged another 104. The 2022 season followed the 2020 and 2021 California wildfire seasons, which had the highest and second-highest (respectively) numbers of acres burned in the historical record, with a sharp drop in acreage burned.
The southwestern North American megadrought is an ongoing megadrought in the southwestern region of North America that began in 2000. At least 24 years in length, the drought is the driest multi-decade period the region has seen since at least 800 CE. The megadrought has prompted the declaration of a water shortage at Lake Mead, the largest reservoir in the United States. Climate change models project drier conditions in the region through the end of the 21st century, though climate change mitigation may avoid the most extreme impacts.
The 2022 New Mexico wildfire season is an ongoing series of wildfires burning throughout the U.S. state of New Mexico. As of December 13, 2022, 904,422 acres (366,007 ha) had burned across the state. The burned acreage figure for 2022 is well above the 1995-2015 average of approximately 270,000 acres burned annually. with the fire season in the state expected to continue until the advent of the regular North American Monsoon weather pattern throughout the Southwestern United States in the summer.
During the summer of 2022, parts of Europe experienced drought conditions exacerbated by heat waves. This was preceded by a warm and dry spring. On 9 August, a senior European Commission researcher said it seems to be Europe's worst year in 500 years. A report from the Global Drought Observatory has confirmed this. The drought had serious consequences for hydropower generation and the cooling systems of nuclear power plants, as the drought reduced the amount of river water available for cooling. Agriculture in Europe was also negatively affected by the drought.
Starting in March 2023, most of Canada experienced drought, which was especially severe across the Prairie provinces and unprecedented in British Columbia. On occasion, every province and territory was in drought at the same time. Common factors across Canada were a quick snow melt, sometimes due to a below-average snowpack, and the warmest May-June period in more than 80 years. Moderate to severe drought conditions from British Columbia to northern Ontario persisted into fall.
