We strive to provide a thorough description on the cutting edge of the spatial and temporal occurrence of rainfall-induced landslides by quantifying the hydro-mechanical processes in hillslopes. Landslides are a pervasive natural phenomenon that constantly shapes the morphology of the earth's surface. Over geologic time, landslides are the result of two episodic, and broadly occurring geologic processes; tectonics and erosion. At human scale, the former operates at a uniform rate barely sensed by humans except during earthquakes. However, the latter is entirely sensible and is driven largely by rainfall. The results of these dynamic geologic processes are the infinite variety of landforms that vary remarkably in geometry; from flat plains to rolling hills, to vertical or even overhanging cliffs, and to shapes that test human's imagination.

Understanding of how landslides occur is vital to the well being of human society and our environment and has been a research focus for many disciplines such as geomorphology, hydrology, geography, meteorology, soil science, and civil and environmental engineering. While each of these disciplines tackles landslide problems from quite different perspectives, a common thread is the mechanics of landsliding. From the vantage of mechanics, no matter how complicated the morphology of the land surface, it is the mechanical balance within hillslopes that determines if they are stable or not. Two coupled physical processes govern the mechanical balance; hydrological or subsurface flow process and stress equilibrium process.