Survey your landscape: What areas or individual plants do you want most to save? Give top priority to irrigating established trees and shrubs; they’re virtually irreplaceable. Consider perennials a second priority.

The roots of various plants grow to different depths; the trick is to apply just enough water to moisten the roots. Most tree roots are located in the top 2 feet of soil. The dripline of a tree or shrub, which runs around the perimeter of the canopy, outlines much of the root zone. Focus water there.

The hose-end device has a needlelike shaft that injects water into the ground, irrigating roots directly so no water is lost to evaporation. Check garden centers for root irrigators like the one from Hound Dog Products (about $20; 800/694-6863). Insert the shaft 6 to 12 inches or deeper into the soil around trees and shrubs. After watering in one spot along the dripline, move the irrigator to another spot until you complete one round-trip. 

Dig down 1 foot with a trowel or spade and feel a handful of soil. An even easier way to test moisture is to use a sampling tube to “read” the soil. When you push the metal tube into the ground and twist it back out, it extracts a 12-inch or longer core, showing in cross section how wet or dry the soil actually is. If the top 2 inches of the soil sample are dry, it’s time to water. Sampling tubes are available from Forestry Suppliers (from $40).

Slow soaking limits runoff and encourages plants to develop deep root systems that are better able to tolerate drought. The heavier your soil, the more important slow soaking is in preventing runoff. Using an oscillating sprinkler to water large areas helps reduce runoff. But if you see puddling, turn the water off for an hour, then start again. To minimize evaporation, irrigate in the early morning or evening.

Mound soil berms around young trees and shrubs such as roses to concentrate water on the root zones. Fill the basin with a slow-running hose so water soaks in.

These porous hoses ooze water along their length. Run them among flowers and shrubs or along hedges or rows of vegetables. Coil them under the driplines of large trees; a good average length is 50 or 100 feet.

-8. Apply mulch

Drought or not, spreading a layer of mulch over the soil around plants is simply good gardening. Mulch reduces evaporation, insulates roots from extreme temperature changes, and helps prevent weeds, which steal water needed by desirable plants. Spread a 3-inch layer of organic mulch such as compost or shredded bark around trees and shrubs; for flowers and vegetables, apply 1 to 2 inches. Gravel and other mineral mulches are also effective.

-9. Modify lawn care

If local restrictions allow lawn irrigation, there are some things you can do to reduce the amount of water you apply. Set your mower to cut at the high end of the recommended range: 1 1/2 inches for bent grass; 2 inches for bluegrass and perennial ryegrass; 3 inches for tall fescue. Taller grass shades the soil, reducing evaporation. In early June, fertilize with 1 pound of nitrogen per 1,000 square feet of turf to strengthen grass before it becomes stressed. In July, cut back to a 1/2 inch of water every week; under this regime, lawns turn the color of straw and go semidormant through summer but bounce back after the weather cools.

Use glazed terra-cotta or plastic ones, which hold water better. For extra insulation, nest smaller pots inside larger ones, or bury pots up to their rims in the ground.

Drought is a recurring feature of the climate in most parts of the world. However, these regular droughts have become more extreme and more unpredictable due to climate change. In fact studies based on dendrochronology, or tree rings dating, confirm that drought affected by global warming goes back to 1900.

Many plant species, such as those in the family Cactaceae (or cacti), have drought tolerance adaptations like reduced leaf area and waxy cuticles to enhance their ability to tolerate drought. Some others survive dry periods as buried seeds. Semi-permanent drought produces arid biomes such as deserts and grasslands.^[4] Prolonged droughts have caused mass migrations and humanitarian crisis. Most arid ecosystems have inherently low productivity. The most prolonged drought ever in the world in recorded history occurred in the Atacama Desert in Chile (400 Years).^[5]

Drought affect food production and human society, so they are considered a disaster, of natural, supernatural or human cause (which itself could be supernatural causes, malediction, sin, ...). It is among the earliest documented climatic events, present in the Epic of Gilgamesh and tied to the Biblical story of Joseph's arrival in and the later Exodus from Ancient Egypt.^[6] Hunter-gatherer migrations in 9,500 BC Chile have been linked to the phenomenon,^[7] as has the exodus of early humans out of Africa and into the rest of the world around 135,000 years ago.^[8] Rituals exist to prevent or avert drought, rainmaking could go from dances to scapegoating to human sacrifices. Nowadays, those ancient practices are for the most part relegated to folklore and replaced by more rational water management.

President Barack Obama discussing the drought in California with farmers, 2014

See also: Dry season

Within the tropics, distinct, wet and dry seasons emerge due to the movement of the Intertropical Convergence Zone or Monsoon trough.^[21] The dry season greatly increases drought occurrence,^[22] 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.^[23] 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).^[24] Periods of warmth quicken the pace of fruit and vegetable production,^[25] increase evaporation and transpiration from plants,^[26] and worsen drought conditions.^[27]

See also: El Niño

Regional impacts of warm ENSO episodes (El Niño)

Drier and hotter weather occurs in parts of the Amazon River Basin, Colombia, and Central America during El Niño events. 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 fires, worsening haze, and decreasing air quality dramatically. Drier-than-normal conditions are also in general observed in Queensland, inland 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 mm of rain falling in the month and temperatures hitting as high as 35 °C on 26 February. The years 1968 and 2005 had the next driest Februaries, when 8.4 mm of rain fell.^[28]

See also: Aeolian processes

Human activity can directly trigger exacerbating factors such as over farming, excessive irrigation,^[29] deforestation, and erosion adversely impact the ability of the land to capture and hold water.^[30] In arid climates, the main source of erosion is wind.^[31] Erosion can be the result of material movement by the wind. The wind can cause small particles to be lifted and therefore moved to another region (deflation). Suspended particles within the wind may impact on solid objects causing erosion by abrasion (ecological succession). Wind erosion generally occurs in areas with little or no vegetation, often in areas where there is insufficient rainfall to support vegetation.^[32]

Fields outside Benambra, Victoria, Australia suffering from drought conditions in 2006.

Loess is a homogeneous, typically nonstratified, porous, friable, slightly coherent, often calcareous, fine-grained, silty, pale yellow or buff, windblown (Aeolian) sediment.^[33] It generally occurs as a widespread blanket deposit that covers areas of hundreds of square kilometers and tens of meters thick. Loess often stands in either steep or vertical faces.^[34] Loess tends to develop into highly rich soils. Under appropriate climatic conditions, areas with loess are among the most agriculturally productive in the world.^[35] Loess deposits are geologically unstable by nature, and will erode very readily. Therefore, windbreaks (such as big trees and bushes) are often planted by farmers to reduce the wind erosion of loess.^[31] Wind erosion is much more severe in arid areas and during times of drought. For example, in the Great Plains, it is estimated that soil loss due to wind erosion can be as much as 6100 times greater in drought years than in wet years.^[36]

See also: Climate change

Global climate change is expected to trigger droughts with a substantial impact on agriculture^[37][38] throughout the world, and especially in developing nations.^[39][40][41] Along with drought in some areas, flooding and erosion could increase in others. Some proposed solutions to global warming that focus on more active techniques, solar radiation management through the use of a space sunshade for one, may also carry with them increased chances of drought.^[42]

According to the Special Report on Climate Change and Land of the Intergovernmental Panel on Climate Change climate change increase drought and desertification. Hundreds of million people are affected. The affected area includes large territories in Africa, Asia, Australia, and South America.^[43]