Deserts Driest Places on Earth

Deserts constitute the second most extensive environment system of the Earth. They are an important sub-component of the global climate system. The book briefly describes how deserts are formed, some great deserts of the world, and desertification, desert landforms, mineral resources in deserts, water in deserts, desert plants, desert animals, and people living in deserts. The book provides a bird’s eye view on the factors accelerating process of desertification and how it will have devastating consequences for both humans and the environment and its possible impact on the climate of even those regions that are quite remote from the actual desert areas and how to stop it.

Dr. Subodh Mahanti did his BSc (Honours) from Burdwan University (1976)and MSc from Banaras Hindu University (1978). He was awarded BHU Gold Medal for standing first in MSc. He did his PhD in Organic Chemistry (1982) and subsequently worked in Molecular Biology. For the last 14 years he has been working in Vigyan Prasar. Besides his research papers, he has written more than 300 popular science articles. He has edited/authored/co-authored more the 20 books. Dr. Mahanti has been awarded FIE Foundation National Award (2000), NCSTC National Award (2003), Delhi Hindi Academy Award (2006) and Dr. Meghand Saha Award (2005) for his contributions in the field of Science Popularisation. Dr. Mahanti is a Fellow of the NCSTC Network.

Earth is the only planet we know of with life on it. Animals, Plants and microorganisms maintain a delicate balance with a variety of life forms we call Biodiversity. Each species depends on other species for its existence. When we talk of life on earth, we also talk about the human species. If we need to understand and preserve our environment, we shall need to understand thee interdependence of the species on each other and the importance of natural resources like air, water and soil for living beings.

Life has continued to evolve on this earth over millions of years adapting to changing environment. Only those species have survived that have adapted to the changing environment. This change could be due to natural causes like earthquakes, eruption of volcanoes, cyclones, and so on. It even could be due to climate change. However, quite often this is brought about by the species higher up in the ladder of evolution that tries to control environment to suit its needs and for development. This is precisely what human species has done to our fragile planet.

We need energy for development; which we traditionally obtain by burning natural resources like firewood, coal and petroleum. This is what we have been doing for centuries. Today there is consensus that human activities like burning of fossil fuels and consequent pumping of gases like carbon dioxide into atmosphere have been responsible for the earth getting hotter and hotter Today, there are threats to our planet arising from climate change, degrading environment, the growing rate of extinction of species, declining availability of fresh water, rivers running dry before they can reach sea, loss of fertile land due to degradation, depleting energy sources, incidence of diseases, challenge of feeding an exponentially growing population, and so on. The human population is now so large that the amount of resources needed to sustain it exceeds what is available. Humanity’s environmental demand is much more that the earth’s biological capacity. This implies that we are living way beyond our means, consuming much more than what the earth can sustain.

To draw the attention of the world to these aspects and in an attempt to establish that environment is where we live and development is what we all do in attempting to improve our lot, within that abode, the United Nations has declared the year 2008 as “The Year of the Planet Earth”. It is hoped that with the cooperation of all we shall be able to save the biodiversity and the life on this planet. A host of activities and programmes are being organized all over the world for this purpose. One of the important aspects is to make people aware about the challenges we face and the possible solution to save this planet form heading towards catastrophe. It is with such thoughts that Vigyan Prasar had initiated programmes with activities built around the theme “The Planet Earth”. The activities comprise of development and production of a series of informative booklets, radio and television programmes, and CD-ROMs; and training of resource persons in the country in collaboration with other agencies and organizations.

It is expected that the present series of publication on the theme “The Planet Earth” would be welcomed by science communicators, science clubs resource persons, and individuals; and inspire them initiate actions to save this fragile abode of ours.

The English word desert comes from the Latin term desertum, meaning “an unpopulated place”, and correctly reflects the harshness of the environment where few, if any live. The common perception about deserts is that these are hot, dry areas where it almost never rains and the dead and dreary sands stretch away as far as the eyes cab see. While there may be an element of truth in this commonly held idea, there are many fascinating facets that xome to life when desert regions are given a closer look. It is correct that deserts are generally dry places on Earth. If a region receives an average of less than 25 centimetres of rain each year, scientists classify it as a desert. But in addition to the hot, dry deserts there are also the so-called Cold deserts. When cold and unmelting snow create environments where life forms face formidable challenges for survival, area is called a cold desert.

Deserts constitute the second most extensive environment system of the Earth. They are an important sub-component of the global climate system. But the threat is that thousands and thousands of hectares of productive land are becoming desert-like and thus, unproductive. This process is termed as desertification. There is enough evidence to indicate that desertification has been occurring extensively over the world for the last several decades. The process of desertification is accelerating and is currently affecting on fifth of the world’s population in more than 100 countries. It has had devastating consequences for both humans and the environment. If desertification continues unabated, it has the potential to seriously impact on the climate of even those regions that are quite remote from the actual desert areas. The process of desertification has therefore come under close scrutiny.

Some scientists think that desertification is a process of change, some others think that it is the end result of the process of change. There are sozens of definitions for the term “desertification”. While some definitions complement each other; others appear to be contradictory. But all agree that desertification – the loss of the land’s biological productivity to arid, semi-arid and dry sub-humid areas –is one of the most serious threats facing humanity. The problem of desertification and deterioration of desert environment has become a global concern. It has been estimated that, if we don’t take action, current trends suggest that by 2020 an estimated 60 million people could move from decertified areas of sub-Saharan Africa towards North Africa and Europe, and that worldwide, 135 million people could be placed at risk of being uprooted.

This book certainly cannot be considered as a comprehensive account on deserts. Its main objective is to provide an introduction to the different facets of deserts. After defining what is meant by deserts, and how they are formed, the book briefly describes the great deserts of the world, desert landforms, mineral resources in deserts, water in deserts, desert plants, desert animals, and people in deserts. Special emphases has been placed on the process of desertification and how to stop it. The glossary section of the book contains definitions of important concept and facts related to deserts and their environments the slight repetitions are intentional and meant to reinforce message.

The theme of the book is very relevant to India and its people. India’s arid zone covers about 39 million hectare (Mha). This is about 12 per cent of the total area of the country. Kofi Annan pointed out in 2003 that every year in India, dry spells and deforestation turn 2.5 million hectares into wasteland, while elsewhere in Asia, sandstorms are becoming a growing threat to the economy and the environment.

A large number of Indians live in deserts. The Thar Desert in Rajasthan is most highly populated hot desert in the world.

We must act now otherwise it would be too late to tackle the situation. It would require collective action. The first step is to create awareness among the people and this book may be perceived as a small effort towards the goal.

After the oceans, deserts are one of the most extensive environment systems and cover vast areas of the Earth. When we talk about the well-being of the Planet Earth or of a sustainable Earth system, we cannot ignore deserts. According to Tony Allan and Andrew Warren deserts (both hot and cold) comprise up to 40 per cent of the terrestrial surface. While this may not be a consensus figure, it can be safely said that one-third of the Earth’ surface is covered by deserts.

Most deserts lie near the Tropic of Cancer and the Tropic of Capricorn-the two lines of latitude lying about 30 degrees from the equator. The area between these two lines is called the Torrid Zone. Almost all continents have deserts. A very high proportion of the continents of Africa and Australia are deserts. Most parts of southwest Asia and Central Asia and all the south-western states of the United States and much of northern Mexico are deserts. Small parts South America are deserts.

When people think of deserts, the following images come to their minds: hot and arid land, no rain, vast expanses of sand, reddish brown soil a brilliant blue sky, no vegetation or very few plants-mostly thorn. The camel is the only to be truly at home in the deserts. But the truth is far removed from this. It is not very common to find sand in a desert. Small rocks, pebbles and loose gravel are to be found on the surface of the most of the deserts. Only about 15-20% of the world’s desert is covered by pure sand. The desert landscapes are the result of the action of wind and water millions of years and some areas are of spectacular natural beauty.

Contrary to what most people believe, all deserts are not hot some desert near the North and South Poles are so cold that all moisture is frozen solid. But, all deserts have two things in common: they are dry, and they support little plant and animal life.

There is a wide temperature variation between day and night in the deserts. Temperatures rise during the day but as the Sun sets, deserts become coolar. Thus deserts alternately warm and cool. This cycle of alternate heating and cooling causes the rocks to cyclically expand and contract. The continuous cycles of expansion and contraction breaks the rocks into smaller fragments. The fragments thus produced are blown away by the desert wind and grind down other rocks. This leads to gradual wearing away of the rocks. As the process continues the fragments eventually form the grain-like sand that we see on desert surfaces.

Desert sand is not the same sand that we find on beaches. Desert sand is larger and rounder. The color of the sands also varies from desert to desert. Most of the sand in deserts is in the form of sand sheets and sand sees – vast regions of undulating dunes resembling ocean waves “frozen” in an instant of time. Sometimes the winds blow away almost all the sand, exposing bare rocks or stony ground.

Deserts are not of recent origin. These have existed throughout the Earth’ history and have persisted for millions of years. Deserts are believed to have been present even when glaciers covered large portions of the Earth during the great Ice Ages. Scientists agree that some deserts, though perhaps samaller than the present ones, have always been present on Earth. A particular desert may disappear because of changes in climate. Similarly a non-desert may region may become a desert. But this kind of transformation does not take place suddenly. It takes a very long time to come to pass. Deserts are not static. They expand and contract within well-defined zones.

Rainfall varies from desert to desert and from year to year. The driest deserts may receive no rainfall for several years. The Atacama Desert has faced the world’s longest drought. In some part of the desert no rain fell here for 400 years (from 1571 until 1971). On the other hand, a desert may receive as much as 430 millimeters of rain in a single year. Rainfall may be spread out over many months or fall within a few hours. For example, in the Astacama Desert again, more than 12.5 millimeters of rain fell in one shower after four years of drought. The point to note here is that the Atacama Desert is considered the world’s driest desert. Such conditions often cause flash floods, which sweep vast quantities of mud, sand, and boulders trough gullies and dry river beds (sometimes called wadis or arroyos). The water, however, soon evaporates or disappears into the ground.