Editing Drought (section)

=== General precipitation deficiency ===
{{See also|Precipitation}}
Mechanisms of producing precipitation include [[convective]], [[Stratus cloud|stratiform]],<ref>{{cite journal|title=A convective/stratiform precipitation classification algorithm for volume scanning weather radar observations|author=Emmanouil N. Anagnostou|journal=[[Meteorological Applications]]|year=2004|volume=11|pages=291–300|doi=10.1017/S1350482704001409|issue=4|bibcode=2004MeApp..11..291A|doi-access=free}}</ref> and [[orographic lift|orographic]] rainfall.<ref>{{cite journal|title=A model of annual orographic precipitation and acid deposition and its application to Snowdonia|author1=A.J. Dore|author2=M. Mousavi-Baygi|author3=R.I. Smith|author4=J. Hall|author5=D. Fowler|author6=T.W. Choularton|journal=Atmospheric Environment|volume=40|date=June 2006|pages=3316–3326|doi=10.1016/j.atmosenv.2006.01.043|issue=18|bibcode=2006AtmEn..40.3316D}}</ref> Convective processes involve strong vertical motions that can cause the overturning of the atmosphere in that location within an hour and cause heavy precipitation,<ref name="convection">{{cite book|author=Robert Penrose Pearce|year=2002|url=https://books.google.com/books?id=QECy_UBdyrcC&pg=PA66|title=Meteorology at the Millennium|publisher=Academic Press|page=66|isbn=978-0-12-548035-2|access-date=2009-01-02}}</ref> while stratiform processes involve weaker upward motions and less intense precipitation over a longer duration.<ref>{{Cite book|title=Cloud dynamics|last=Houze|first=Robert A. Jr.|date=1993|publisher=Academic Press|isbn=9780080502106|location=San Diego|oclc=427392836}}</ref>

Precipitation can be divided into three categories, based on whether it falls as liquid water, liquid water that freezes on contact with the surface, or ice.

Droughts occur mainly in areas where normal levels of rainfall are, in themselves, low. If these factors do not support precipitation volumes sufficiently to reach the surface over a sufficient time, the result is a drought. Drought can be triggered by a high level of reflected sunlight and above average prevalence of high [[pressure system]]s, [[wind]]s carrying continental, rather than oceanic air masses, and ridges of [[high pressure area]]s aloft can prevent or restrict the developing of thunderstorm activity or rainfall over one certain region. Once a region is within drought, feedback mechanisms such as local arid air,<ref>{{cite book|url=https://books.google.com/books?id=3lbixDAw5DwC&pg=PA22|page=22|title=Greenhouse Effect, Sea Level and Drought|author1=Roland Paepe|author2=Rhodes Whitmore Fairbridge|author3=Saskia Jelgersma|date=1990|publisher=Springer Science & Business Media|isbn=978-0792310174}}</ref> hot conditions which can promote warm core ridging,<ref>{{cite book|url=https://books.google.com/books?id=PvJyVtw53Y4C&pg=PA48|pages=48–49|title=The Oryx Resource Guide to El Niño and La Niña|author1=Joseph S. D'Aleo|author2=Pamela G. Grube|date=2002|publisher=Greenwood Publishing Group|isbn=978-1573563789}}</ref> and minimal evapotranspiration can worsen drought conditions.

==== Dry season ====
{{See also|Dry season}}

Within the tropics, distinct, [[wet season|wet]] and dry [[season]]s emerge due to the movement of the [[Intertropical Convergence Zone]] or [[Monsoon trough]].<ref name="Wang">{{cite book|author=Bin Wang|url=https://books.google.com/books?id=yRT57TENzT8C&pg=PT206|title=The Asian Monsoon|date=2006-01-13|publisher=Springer Science & Business Media|isbn=978-3540406105|page=206}}</ref> The dry season greatly increases drought occurrence,<ref>{{cite book|url=https://books.google.com/books?id=y6r9jUTzJiYC&pg=PA349|page=349|title=Monitoring and Predicting Agricultural Drought : A Global Study: A Global Study|author1=Vijendra K. Boken|author2=Arthur P. Cracknell|author3=Ronald L. Heathcote|date=2005-03-24|isbn=978-0198036784|publisher=Oxford University Press}}</ref> and is characterized by its low humidity, with watering holes and rivers drying up. Because of the lack of these watering holes, many grazing animals are forced to migrate due to the lack of water in search of more fertile lands. Examples of such animals are [[zebras]], [[elephants]], and [[wildebeest]]. Because of the lack of water in the plants, bushfires are common.<ref>{{cite web|url=http://burarra.questacon.edu.au/pages/seasons.html|title=Wet & Dry Seasons|access-date=2018-12-23|archive-url=https://web.archive.org/web/20120320141721/http://burarra.questacon.edu.au/pages/seasons.html|archive-date=2012-03-20|url-status=dead}}</ref> Since water vapor becomes more energetic with increasing temperature, more water vapor is required to increase relative humidity values to 100% at higher temperatures (or to get the temperature to fall to the dew point).<ref>{{cite web|url=http://www.ems.psu.edu/~fraser/Bad/BadClouds.html|title=Bad Meteorology: The reason clouds form when air cools is because cold air cannot hold as much water vapor as warm air|author=Alistair B. Fraser|date=1994-11-27|access-date=2015-02-17|archive-url=https://web.archive.org/web/20150316122724/http://www.ems.psu.edu/~fraser/Bad/BadClouds.html|archive-date=2015-03-16|url-status=dead}}</ref> Periods of warmth quicken the pace of fruit and vegetable production,<ref>{{cite book|url=http://www2.ca.uky.edu/agc/pubs/id/id128/id128.pdf|archive-url=https://ghostarchive.org/archive/20221009/http://www2.ca.uky.edu/agc/pubs/id/id128/id128.pdf|archive-date=2022-10-09|url-status=live|page=19|title=Home Vegetable Gardening in Kentucky|author=Cooperative Extension Service|publisher=[[University of Kentucky]]|date=January 2014|access-date=2015-02-18}}</ref> increase evaporation and transpiration from plants,<ref>{{cite web|author=North Carolina State University|title=Evapotranspiration|url=https://www.nc-climate.ncsu.edu/edu/k12/.evapo|date=2013-08-09|access-date=2015-02-18|archive-url=https://web.archive.org/web/20150219045714/https://www.nc-climate.ncsu.edu/edu/k12/.evapo|archive-date=2015-02-19|url-status=dead|author-link=North Carolina State University}}</ref> and worsen drought conditions.<ref>{{cite web|url=http://www.noaanews.noaa.gov/stories/s909.htm|date=2002-05-16|access-date=2015-02-18|title=Warm Temperatures and Severe Drought Continued in April Throughout Parts of the United States; Global Temperature For April Second Warmest on Record|author=National Oceanic and Atmospheric Administration|url-status=dead|archive-url=https://web.archive.org/web/20150219055008/http://www.noaanews.noaa.gov/stories/s909.htm|archive-date=Feb 19, 2015}}</ref>

==== El Niño–Southern Oscillation (ENSO) ====
{{Further|El Niño–Southern Oscillation}}
The [[El Niño–Southern Oscillation]] (ENSO) phenomenon can sometimes play a significant role in drought. ENSO comprises two patterns of temperature anomalies in the central [[Pacific Ocean]], known as [[La Niña]] and [[El Niño]]. La Niña events are generally associated with drier and hotter conditions and further exacerbation of drought in [[droughts in California|California]] and the [[Southwestern United States]], and to some extent the [[Southeastern United States|U.S. Southeast]]. Meteorological scientists have observed that La Niñas have become more frequent over time.<ref>{{cite web|url=https://www.9news.com/article/news/nation-world/la-nina-west-coast-climate/507-f792ab4a-bc35-4e45-9de1-08d8379dfc9b|title=Weather's unwanted guest: Nasty La Niña keeps popping up|author=Seth Borenstein|publisher=9news.com.au.com|date=May 28, 2022|access-date=June 4, 2022|quote=Scientists are noticing that in the past 25 years the world seems to be getting more La Niñas than it used to...|url-status=live|archive-url=https://archive.today/20231206185338/https://www.9news.com/amp/article/news/nation-world/la-nina-west-coast-climate/507-f792ab4a-bc35-4e45-9de1-08d8379dfc9b|archive-date=6 December 2023}}</ref>

Conversely, during El Niño events, drier and hotter weather occurs in parts of the [[Amazon River]] Basin, [[Colombia]], and [[Central America]]. Winters during the El Niño are warmer and drier than average conditions in the Northwest, northern Midwest, and northern Mideast United States, so those regions experience reduced snowfalls. Conditions are also drier than normal from December to February in south-central Africa, mainly in [[Zambia]], [[Zimbabwe]], [[Mozambique]], and [[Botswana]]. Direct effects of El Niño resulting in drier conditions occur in parts of [[Southeast Asia]] and [[Northern Australia]], increasing [[bush fire]]s, worsening [[haze]], and decreasing air quality dramatically. Drier-than-normal conditions are also in general observed in [[Queensland]], inland [[Victoria (Australia)|Victoria]], inland [[New South Wales]], and eastern [[Tasmania]] from June to August. As warm water spreads from the west Pacific and the [[Indian Ocean]] to the east Pacific, it causes extensive drought in the western Pacific. Singapore experienced the driest February in 2014 since records began in 1869, with only 6.3&nbsp;mm of rain falling in the month and temperatures hitting as high as 35&nbsp;°C on 26 February. The years 1968 and 2005 had the next driest Februaries, when 8.4&nbsp;mm of rain fell.<ref>{{cite web|url=http://www.channelnewsasia.com/stories/singaporelocalnews/view/1040778/1/.html|publisher=Channel NewsAsia|title=February 2010 is driest month for S'pore since records began in 1869|first1=Joanne|last1=Chan|date=3 March 2010|access-date=5 November 2017|archive-url=https://web.archive.org/web/20100303222328/http://www.channelnewsasia.com/stories/singaporelocalnews/view/1040778/1/.html|archive-date=3 March 2010}}</ref>