Preface

Aridity is the imbalance between long-term average water supply and long-term average water demand. Unlike drought, which is defined as a period of abnormally dry air long enough to cause a serious hydrological imbalance, aridity is permanent, not temporary. A region is arid when it is characterized by a severe lack of usable water inhibiting the growth and development of plant and animal life. Environments exposed to arid climates tend to be devoid of vegetation and are called arid or desert. In the more extreme areas, called extreme arid deserts, the average annual precipitation is below 25mm, under which conditions microorganisms must cope with not only water scarcity but also deadly UV radiation, high and low temperatures, high evaporation rates, prolonged drying times, oligotrophic conditions, and high salinity levels. Arid environments cover more than one-third of the world's land area and represent the most common habitat on Earth after the oceans. Aridity poses a threat to the environment, as well as to the economy and to security, development, food security, and social life around the world. The causes of increased aridity are complex and are thought to be both natural and man-made. Factors such as climate change, population growth, soil erosion, inappropriate irrigation, poor farming methods, soil, water, and groundwater contamination, urbanization, deforestation, improper water management, and desertification of arid and semi-arid zones are among the causes of drought.

A report by the European Commission Joint Research Center on climate change, aridity, and drought states that people around the world feel the effects of climate and environmental crises mostly through water: in the last 50 years, climate and water hazards accounted for half of all disasters and 45 percent of all deaths. The report notes that 90 percent of environment-related casualties during this period occurred in developing countries. Drought is among the greatest threats to sustainable development, especially in developing countries, and a third of the world's population lives in drought-stricken regions. Drought has directly caused the death of approximately 650,000 people in the last half-century. It is reported that approximately 160 million children are currently exposed to severe and prolonged drought, and this situation poses a serious threat to the education, health, and safety of especially women and girls in developing countries. Taking urgent measures on a global scale to combat desertification, water scarcity, loss of agricultural lands, migrations due to desertification and aridity that causes economic losses; determining sustainable land reclamation and ecosystem restoration policies; and steps to be taken against climate change are of vital importance in the fight against aridity and drought.

This edited collection contains seven chapters. Chapter 1 is a general introduction to the topic of aridity and relevant definitions. Chapter 2 highlights drought and water stress in Northern African countries and outlines the main approaches to improving water management in every country of the region. Chapter 3 focuses on the initiatives taken by the Barind Multipurpose Development Authority to transform the aridlike Barind area into a green arable landscape through efficient water management.

Chapter 4 reviews remote sensing tools in agricultural applications. A novel model predicting transported soil volume through the presence of water which is presented in Chapter 5 will be a point of reference in future studies involving rocky planets. Chapter 6 illustrates the impacts of the industrial and technological revolution on territories and cities in arid environments with a case study of the Antofagasta region in the Atacama Desert, Chile. The final chapter evaluates the wood quality of five elite four-year-old Eucalyptus spp. clones from a clonal test installed in a pulp-producing region of seasonal drought stress in central-western Brazil.

> **Murat Eyvaz** Associate Professor, Department of Environmental Engineering, Gebze Technical University, Kocaeli, Turkey
