Water makes up nearly three-fourths of the Earth’s surface and is the most abundant substance on the face of the Earth. Yet as common as it is, water is also the most precious substance on our planet. Contradiction? Not when you think about how much of the Earth’s water is really available for humans: Scientists estimate that less than 1% of water is available for human use. The oceans are made up of more than 97% of the water on earth, while glaciers lock up another 2% of the earth’s water. Of the 1% available for human use, half lies a half-mile below the surface of the earth, out of the reach of man. The remaining water supply is in rivers, lakes and groundwater.
The never-ending worldwide process of water circulation from clouds to land and back to the ocean is called the water cycle, or hydrologic cycle.
Humans interrupt that cycle by bringing water into our homes, schools and cities.
Almost no new water is created in nature. The earth’s water is millions of years old, or older, and is constantly being recycled. We’ve been using the same water since the beginning of time!
In desert areas, like Phoenix, precipitation is limited. All plants and animals must adapt themselves to the environment in which they live.
Desert animals and plants adapt to the stresses of limited moisture and intense radiation from the sun. They have developed ways to conserve, store and gather water, as well as to protect themselves from the sun’s rays:
The saguaro cactus is capable of accordion-like contraction and expansion for water storage. It takes approximately 50 years for a saguaro to produce flowers and approximately 70 years to grow arms.
The ocotillo is a large, thorny shrub that has long, whip-like stems. To reduce water loss, its leaves fall off when conditions are dry. New leaves will grow after a rain. It has medium-sized leaves which have less surface area for evaporation.
An evergreen shrub with small, resinous leaves, the creosote plant has both a taproot for deep-water absorption and shallow roots to help it absorb water quickly during sporadic rainfall. Small, waxy leaves help to seal in moisture.
The kangaroo rat is unique since it can live without drinking water. It gets water from a diet of dried seeds. Urine is concentrated, thereby conserving water. They burrow beneath vegetation during the hottest part of the day; since they don’t sweat or pant, they don’t lose water through perspiration.
The desert tortoise lives in underground burrows that are warm in winter and cool in summer. While estivating (the summer version of hibernating) in the summer, it lives off the fat stored in its body. This tortoise only drinks during rains and stores urine in its large bladder.
People have occupied the Sonoran desert for at least 15,000 years. While plants and animals have certain characteristics which help them to survive in the desert, humans were not designed for desert life. Instead, they attempt to modify their environment to cope with the problems of limited water and hot temperatures.
SRP has brought water to desert dwellers by building a series of six reservoirs on the Salt and Verde Rivers, and 1,230 miles of canals and ditches. The reservoirs capture and store rainfall and snowmelt from the 13,000 square mile watershed.
Because of the limited supply of water in the desert, SRP must manage the water carefully to make sure there is enough:
Only 5% of the precipitation that falls on the Salt and Verde watershed ends up in the SRP lakes.
SRP lakes hold more than 2 million acre-feet of water. This is about a two-year supply.
Approximately 125,000 acre-feet of water are lost each year to evaporation and seepage.