The continued aridity trend occurring in many regions worldwide is a manifestation of the response of the earth system to global change. It hinders severely the sustainable development of these regions. Northern China is one of the largest and most affected regions in the world. This book documents the climate change in its arid and semi-arid areas on decadal to geological time scales based on analyses of various data sources. These analyses improved our understanding of the potential mechanisms driving the aridity trend, particularly in the second half of the 20th century. Based on these analyses and a systematic assessment of the impact of the aridity trend on the ecological and hydrological processes in northern China, measures of human adaptation to the aridity trend for socio-economic developments are proposed.