Oasis

a fertile area that rises in a desert whenever water is regularly available

Wadis

a dry riverbed that fills with water when rare rain fall in a desert

Semiarid

having lower temperatures and cooler nights than hot, dry deserts

Vary

to show difference between things

Millenium

a period of a thousand years

Polytheism

the belied in more than one god

Monotheism

the belief in one god

Expand

to spread out; to grow larger

Collapse

a sudden failure, breakdown, or ruin

Hydropolitics

the politics surrounding water access and usage rights

Fossil water

water that fell as rain thousands of years ago and is now trapped deep below ground

Delta

an area where sand, silt, clay, or gravel is dropped at the mouth of a river

Silt

small particles of rich soil

Ergs

a large area of sand

Nomads

a person who lives by moving from place to place to follow and hunt herds of migration animals or lead herds of grazing animals to fresh pasture

Aquifer

an underground layer of rock through which water flows

Hieroglyphics

the system of writing that uses small pictures to represent sound or words

Caliph

the successor to Muhammad

Demonstrate

to show

Regime

a government