Aiguo Dai reviews drought trends over the last millennium and recent global aridity changes from 1950 to 2008. He discusses future aridity projections based on climate models, noting that prolonged droughts have occurred in North America, West Africa, and East Asia, often linked to tropical sea surface temperature (SST) anomalies. La Niña-like SSTs cause drought in North America, while El Niño-like SSTs cause drought in East China. In Africa, the southward shift of warm SSTs in the Atlantic and warming in the Indian Ocean are responsible for recent Sahel droughts. Local feedbacks can enhance and prolong droughts. Since the 1970s, global aridity has increased due to drying in Africa, southern Europe, East and South Asia, and eastern Australia. Recent warming has increased atmospheric moisture demand and altered circulation patterns, contributing to drying. Climate models project increased aridity in the 21st century over most of Africa, southern Europe, the Middle East, most of the Americas, Australia, and Southeast Asia. The United States has avoided prolonged droughts in the last 50 years but may face persistent droughts in the next 20–50 years. Future drought predictions depend on models' ability to predict tropical SSTs. Drought is a recurring extreme climate event characterized by below-normal precipitation. It is classified into meteorological, agricultural, and hydrological droughts. Meteorological drought is defined by below-normal precipitation, often preceded by above-normal temperatures. Agricultural drought results from dry soils, while hydrological drought involves reduced river flow and groundwater storage. Drought indices, such as the Palmer Drought Severity Index (PDSI), are used to quantify drought. The PDSI considers both precipitation and temperature, making it useful for low and middle latitudes. However, it may not account for all factors affecting drought, such as vegetation and frozen soils. Historical droughts have occurred in many regions, including North America, Africa, Asia, and Australia. The Dust Bowl drought in the 1930s was exacerbated by overgrazing and dust storms. Recent droughts in Africa and East China are linked to SST patterns and warming. Since the 1950s, global aridity has increased, with drying in Africa, southern Europe, East and South Asia, and eastern Australia. The 21st century is projected to see increased aridity in many regions, with climate models showing continued drying over most of Africa, southern Europe, the Middle East, most of the Americas, Australia, and Southeast Asia. Human activities, particularly greenhouse gas emissions, have contributed to recent drying trends. Future drought predictions will depend on accurate modeling of tropical SSTs and other climate factors. Current climate models have limitations in simulating tropical precipitation and variability, requiring further improvements for reliable drought predictions.Aiguo Dai reviews drought trends over the last millennium and recent global aridity changes from 1950 to 2008. He discusses future aridity projections based on climate models, noting that prolonged droughts have occurred in North America, West Africa, and East Asia, often linked to tropical sea surface temperature (SST) anomalies. La Niña-like SSTs cause drought in North America, while El Niño-like SSTs cause drought in East China. In Africa, the southward shift of warm SSTs in the Atlantic and warming in the Indian Ocean are responsible for recent Sahel droughts. Local feedbacks can enhance and prolong droughts. Since the 1970s, global aridity has increased due to drying in Africa, southern Europe, East and South Asia, and eastern Australia. Recent warming has increased atmospheric moisture demand and altered circulation patterns, contributing to drying. Climate models project increased aridity in the 21st century over most of Africa, southern Europe, the Middle East, most of the Americas, Australia, and Southeast Asia. The United States has avoided prolonged droughts in the last 50 years but may face persistent droughts in the next 20–50 years. Future drought predictions depend on models' ability to predict tropical SSTs. Drought is a recurring extreme climate event characterized by below-normal precipitation. It is classified into meteorological, agricultural, and hydrological droughts. Meteorological drought is defined by below-normal precipitation, often preceded by above-normal temperatures. Agricultural drought results from dry soils, while hydrological drought involves reduced river flow and groundwater storage. Drought indices, such as the Palmer Drought Severity Index (PDSI), are used to quantify drought. The PDSI considers both precipitation and temperature, making it useful for low and middle latitudes. However, it may not account for all factors affecting drought, such as vegetation and frozen soils. Historical droughts have occurred in many regions, including North America, Africa, Asia, and Australia. The Dust Bowl drought in the 1930s was exacerbated by overgrazing and dust storms. Recent droughts in Africa and East China are linked to SST patterns and warming. Since the 1950s, global aridity has increased, with drying in Africa, southern Europe, East and South Asia, and eastern Australia. The 21st century is projected to see increased aridity in many regions, with climate models showing continued drying over most of Africa, southern Europe, the Middle East, most of the Americas, Australia, and Southeast Asia. Human activities, particularly greenhouse gas emissions, have contributed to recent drying trends. Future drought predictions will depend on accurate modeling of tropical SSTs and other climate factors. Current climate models have limitations in simulating tropical precipitation and variability, requiring further improvements for reliable drought predictions.