Hydrological Systems, Drought, and Water Insecurity

Vocabulary flashcards covering the physical and human causes of drought, water insecurity, ENSO cycles, and climate change impacts on the global hydrological system.

Teleconnections

Significant relations or links between weather phenomena at widely separated locations on Earth, typically entailing climate patterns that span thousands of miles.

Hadley Cell Expansion

The poleward movement of the Hadley cell by up to $2^\circ$ (approximately $140\text{ miles}$) since 1979 caused by global warming and increased evaporation at the equator, contributing to a $20\text{--}30\%$ summer rainfall reduction in Greece and up to a $45\%$ rainfall drop in central Chile.

El Niño Southern Oscillation (El Niño Phase)

A climatic phase where weakened trade winds reduce the westward movement of warm equatorial water, resulting in less warm water, reduced rainfall, and droughts in Australia and the Western Pacific, while causing excess rainfall in South America.

Normal Pacific Atmospheric Circulation

A state in which equatorial trade winds push warm surface water westward toward Australia to generate clouds and rainfall, while cold, nutrient-rich water is drawn up from the ocean depths along the coast of South America via the Humboldt Current.

Desertification

The process by which fertile and productive land in dry regions loses its nutrients, water, and vegetation, turning into an unproductive desert area.

Wind Erosion in Desertification

The physical process where altered rainfall patterns lead to vegetation die-off, leaving soil exposed to wind erosion at a rate of $24\text{ billion tonnes}$ per year and preventing the remaining soil from absorbing moisture.

Sahelian Water Deficit

Severe water stress driven by rapid human population growth ($3\%$ per year), overgrazing, over-cultivation, civil wars, and over-abstraction of groundwater, resulting in Lake Chad's surface area shrinking by over $90\%$ between the 1960s and 2000s.

Australia's "Big Dry" Event

The most severe prolonged climate event in Australia's history ($1996\text{--}2010$), causing rice production to collapse by $99\%$, sheep populations to halve, cotton outputs to plummet, and cities to invest over \\$13\text{ billion} in desalination plants.

Ecological Resilience

The capacity of an ecosystem to withstand and recover from a natural disturbance (such as drought or flood) or human disturbance.

Wetland Ecosystems

Areas covered in water for extended periods that recharge aquifers, act as natural retention zones to mitigate flood risk, support diverse species habitats, and use vegetation and dilution to filter and reduce the concentration of pollutants.

Continentality

A physical factor causing water insecurity in the interior of large continental landmasses, where inland moisture availability is very low due to vast distances from the ocean.

Geological Controls on Water Security

The influence of bedrock permeability on water availability: permeable bedrock allows aquifer formation (e.g., providing $70\%$ of China's irrigation water), whereas impermeable bedrock prevents natural underground water storage.

Blue Baby Syndrome

A severe health issue linked to agricultural water contamination, caused by nitrate pollution leaching from chemical fertilizers into water supplies.

Untreated Sewage Discharge

A human cause of water contamination that introduces pathogens like cholera into water supplies; globally, the UN estimates $80\%$ of wastewater is discharged untreated, including $70\%$ of all sewage in India.

Industrial Water Contamination in China

Severe chemical pollution of freshwater stores where $78\%$ of lakes and $80\%$ of rivers are fit only for industrial use rather than human consumption, including discharges containing lead and arsenic in the Yangtze River.

Top Global Water Users

The three largest annual consumers of freshwater: India ($647.5\text{ billion cubic metres}$, $90\%$ used for agriculture), China ($591.8\text{ billion cubic metres}$), and the USA ($444.4\text{ billion cubic metres}$).

Virtual Water Footprint (Agriculture)

The total volume of freshwater consumed to produce agricultural products, exemplified by the $2500\text{ L}$ required to produce $1\text{ kg}$ of rice compared to the $18,000\text{ L}$ required to produce $1\text{ kg}$ of beef.

Economic Water Scarcity

A condition in which water availability is restricted by a lack of capital, infrastructure, technology, or poor governance rather than a physical absence of water.

Water Privatisation in Bolivia (1999)

A policy event in Bolivia in 1999 that led to a $35\%$ increase in the cost of water, illustrating how market privatisation can induce economic water scarcity.

Water Poverty Disparity (UK vs. Ghana)

An economic disparity where $50\text{ L}$ of tap water costs $10\text{p}$ in the UK, compared to $50\text{p}$ in Ghana, the latter representing $25\%$ of an informal worker's daily income.

Albedo

A measure of the reflectivity of a surface, expressed as the percentage of incoming solar radiation (sunlight) that is reflected back into space.

Arctic Amplification

A positive feedback process where thawing white ice surfaces (high albedo) give way to darker blue ocean water, increasing solar absorption and further accelerating warming.

Enhanced Greenhouse Effect

The heightened trapping of heat in the atmosphere driven by human emissions, causing more re-radiated and re-emitted heat to remain in the Earth system and less heat to escape into space.

Precipitation Trends under Climate Change

Hydrological shifts caused by warmer air having a higher water-holding capacity, which increases precipitation intensity over frequency, decreases rainfall between $10^\circ$ and $30^\circ$ of the equator, and causes winter precipitation in northern regions to fall as rain rather than snow.

Biotic Pumping

The natural process by which forest vegetation recycles moisture and drives evapotranspiration to maintain rainfall; disrupted by widespread deforestation, reducing natural water retention for $75\%$ of the world's largest cities.