White Sands National Monument in New Mexico, Wadi Dhar in Yemen, and Dead Vleii in the Namib Desert are provided as examples of desert locations. Deserts are defined as areas receiving less than 250mm of annual precipitation, or less than 100mm for extreme deserts. Deserts experience large daily temperature fluctuations. Common desert landforms include hamadas (rock deserts), ergs (sand deserts), stony deserts, playas (dry lake beds), wadis (dry river beds), and bajadas (alluvial fans). Desert vegetation is xerophytic or drought-resistant, with small, twisted leaves and stomata that only open at night. Perenn

1. White Sands National Monument, New Mexico, USA Wadi Dhar, Yemen Dead Vleii, Namib Desert DESERT INTRODUCTION

2. DISTRIBUTION OF DESERTS Annual precipitation in deserts is less than 250mm and less than 100mm in extreme deserts. Deserts have large diurnal temperature ranges.

8. Hot Desert Climates

10. Rock desert or hamada Sand desert or erg Stony desert

11. Basins of inland drainage called playas or shotts Dry ravines or wadis or arroyos Alluvial fans can join together to form a bajada

12. DESERT VEGETATION

13. This xerophytic or drought resistant vegetation has adapted to living in dry conditions by having small, twisted leaves with stomata which only open at night to allow respiration.

14. Perennials, such as ocotillo, become dormant between the rains. Once all moisture has evaporated from the soil, the plant drops its leaves and temporarily stops growing.

15. Instead of thorns, the creosote bush relies for protection on a smell and taste that wildlife find unpleasant. Creosote has an extensive double root system -- both radial and deep -- to accumulate water from both surface and ground water.

16. Cactus, xerophytic adaptations of the rose family, are among the most drought-resistant plants on the planet due to their absence of leaves, shallow root systems, ability to store water in their stems, spines for shade and waxy skin to seal in moisture.

17. Desert plants must act quickly when heat, moisture and light inform them it's time to bloom. Ephemerals are the sprinters of the plant world, sending flower stalks jetting out in a few days. The peak of this bloom may last for just days or many weeks, depending on the weather and difference in elevation.

18. WATER? IN THE DESERT?

19. RAINFALL

20. RAINFALL

21. RAINFALL

22. RIVER

23. RIVER

24. RIVER

25. RIVER

26. GROUNDWATER

27. GROUNDWATER

28. GROUNDWATER

29. Resources and Further Reading Robert G. Bailey (1998), Ecoregions, Springer-Verlag New York Farouk El-Baz et al.,(1982), The Desert Realm, National Geographic Tony Allan & Andrew Warren (1993), Deserts, Mitchell Beazley World Conservation Atlas www.geojuice.org