Geol 1418 Drought

Drought

A deficiency of precipitation over an extended period, resulting in a water shortage.

Stealth Disaster

Drought proceeds slowly and progressively, often without immediate attention.

Fatal Impacts

Drought has caused more deaths, displacement, and wars than any other natural disaster.

Duration

Can affect broad areas and last months, years, or decades.

U.S. Losses

Annual $6–8 billion in damages.

Widespread Drought

Covers over 40% of the U.S. every few years.

Unique Nature

Drought differs from other natural processes due to gradual onset and accumulating impacts.

Definition (NWS)

“A deficiency of precipitation over an extended period (usually a season or more) resulting in a water shortage.”

Not Always Dry

Drought doesn’t require extremely dry conditions, just less precipitation than usual.

Relative Phenomenon

Drought and “normal” vary region to region.

Example (San Francisco vs. Reno)

Both faced extreme drought in 2014 despite vastly different normal rainfall averages.

Meteorological Drought

When precipitation is below normal for weeks to years.

Agricultural Drought

When soil moisture fails to meet crop needs.

Hydrological Drought

When surface and subsurface water supplies fall below normal.

Socioeconomic Drought

When water supply fails to meet human and environmental demands.

Most Common Cause

A persistent departure from normal weather patterns.

U.S. Drought Formation

Caused by repeated high-pressure systems staying over one area.

High-Pressure Systems

Bring light winds, clear skies, and dry conditions.

Palmer Drought Severity Index (PDSI)

Measures moisture deficiency compared to average local conditions.

US Drought Monitor

Map combining climate, soil, and hydrologic data to summarize drought conditions.

Drought Severity Classification

Used to rank drought intensity levels.

Consequences of Drought

Famine, livestock deaths, migration, war, and civilization collapse.

Historical Collapses

Egypt, Greece, Angkor Wat all fell partly due to drought.

Mayan Civilization

Declined due to century-long rainfall decreases and multiple severe droughts.

Mayan Impact

Abandonment of cities, halted monument building, and wars.

Droughts in China

1877–78: 9.5 million dead; 1928–30: 3 million dead; 1958–61: up to 45 million dead.

Dust Bowl (1930s)

Multi-year U.S. drought that devastated Great Plains agriculture.

Term “Dust Bowl”

Coined by AP reporter Robert Geiger (1935).

Dust Bowl States

Kansas, Colorado, Oklahoma, Texas, New Mexico.

Four Distinct Droughts

Occurred in 1930–31, 1934, 1936, 1939–40.

Causes of Dust Bowl Damage

Poor land management, Great Depression, overexpansion, lack of conservation.

Migration West

Thousands of farms abandoned; families moved to California and western states.

Cultural Legacy

Captured in The Grapes of Wrath by John Steinbeck (1939).

New Deal Relief

Programs under FDR created drought recovery and prevention systems.

Relief Measures

Emergency supplies, livestock aid, farm loans, reforestation.

Soil Conservation Service (SCS)

Created to promote long-term drought resilience (now NRCS).

Desertification

Process turning productive land into desert, often due to poor land management.

Main Desertification Causes

Overgrazing, marginal farming, vegetation loss, poor irrigation.

Salinization

Salt buildup in soil from improper irrigation, preventing plant growth.

Population Pressure

Overuse of land and poverty worsen desertification.

Sahel Region

Semi-arid African region where desert moved 100 km south (1950–1975).

Restricted Herding

Closed borders in Sudan worsened vegetation loss and desert spread.