A drought is a prolonged period of abnormally low precipitation that results in a noticeable water shortage for people, agriculture, and the environment. This natural hazard develops slowly over weeks or months, making its beginning and end difficult to pinpoint. Understanding a drought requires looking beyond simple rainfall deficits to examine its complex and varied impacts. Two interesting facts about droughts are the multiple ways they are scientifically measured and their hidden, damaging physical effects on built infrastructure.
The Four Dimensions of Drought Measurement
Drought is classified into four distinct types, each reflecting a different impact on the Earth’s systems. The progression usually begins with a meteorological deficit, which is a lack of rainfall over an extended time compared to the regional average. This initial lack of moisture then cascades into other systems.
The immediate consequence of a rainfall deficit is an agricultural drought, which focuses on soil moisture levels. When water in the soil is insufficient to support crop health, it leads to reduced yields and crop failure. This type is the first to become apparent after a meteorological drought begins.
If dry conditions persist, a hydrological drought follows, characterized by below-average water levels in surface and subsurface reserves. This includes reduced stream flow, lower water tables in aquifers, and decreased storage in reservoirs. Hydrological deficits take longer to develop because large water bodies and groundwater systems have a significant buffer capacity.
Finally, a socioeconomic drought occurs when physical water shortages affect the supply and demand of economic goods. This dimension considers the human impact, such as financial losses in agriculture, increased costs for energy production, or the need for water-rationing policies. The four classifications demonstrate that a drought’s severity is measured by its impact, not just the amount of rain that failed to fall.
Hidden Physical Effects on Infrastructure
A less obvious consequence of extended dry periods is the physical damage they inflict on man-made structures and the ground beneath them. This damage is most pronounced in areas with high clay content soils, known as expansive soils. As these soils lose moisture during a drought, they undergo desiccation and contract sharply.
This shrinkage can remove support from building foundations, roads, and utility lines, leading to structural instability. The soil contraction causes differential settlement, where various parts of a foundation sink at different rates. This results in cracks in walls, ceilings, and basement floors. Homeowners may notice signs like doors and windows that suddenly stick or become misaligned because the structure is shifting.
A related physical effect is land subsidence, which occurs in regions that rely heavily on groundwater pumping. When drought conditions force increased extraction from underground aquifers, the pressure the water once exerted on the surrounding soil is reduced. This pressure drop can cause the fine-grained soil layers to compact permanently, leading to the sinking of the ground surface. This compaction is irreversible and can damage deep foundations, bridges, and buried infrastructure like pipelines and sewer systems.