The following table shows the extent of drought by major region (abbreviated) by listing the percent of normal precipitation. Drought here is arbitrarily defined as when there is less than 75 percent of normal precipitation. There was no drought in any region in the years not listed. Note that in 2011, as well as 1917 and 1956, all the regions were in drought. Source: Office of State Climatologist, Texas A&M University.
Drought has proven to be difficult to define and there is no universally accepted definition. The most commonly used drought definitions are based on meteorological, agricultural, hydrological and socioeconomic effects. (These definitions are from the New Mexico Drought Planning Team website.)
Meteorological drought is often defined by a period of substantially diminished precipitation duration and/or intensity. The commonly used definition of meteorological drought is an interval of time, generally on the order of months or years, during which the actual moisture supply at a given place consistently falls below the climatically appropriate moisture supply.
Agricultural drought occurs when there is inadequate soil moisture to meet the needs of a particular crop at a particular time. Agricultural drought usually occurs after or during meteorological drought but before hydrological drought and can also affect livestock and other dry-land agricultural operations.
Hydrological drought refers to deficiencies in surface and subsurface water supplies. It is measured as streamflow and as lake, reservoir and groundwater levels. There is usually a delay between lack of rain and less measurable water in streams, lakes and reservoirs. Therefore, hydrological measurements tend to lag other drought indicators.
Socioeconomic drought occurs when physical water shortages start to affect the health, well-being, and quality of life of the people, or when the drought starts to affect the supply and demand of an economic product.