Running water is undoubtedly the most dominating geomorphic agent in shaping the earth's surface in both humid and arid climates.

In humid regions, which receive heavy rainfall, running water is considered the most important agent in bringing about the degradation of the land surface. There are two components of running water: overland flow on general land surface as a sheet, and linear flow as streams and rivers in valleys. Most of the erosional landforms made by running water are associated with vigorous and youthful rivers flowing over steep gradients. With time, stream channels over steep gradients turn gentler due to continued erosion, and as a consequence, lose their velocity, facilitating active deposition.

In arid climates or deserts, many features owe their formation to mass wasting and running water as sheet floods. Though rain is scarce in deserts, it comes down torrentially in a short period of time. The desert rocks, devoid of vegetation and exposed to mechanical and chemical weathering processes due to drastic diurnal temperature changes, decay faster. The torrential rains help in removing the weathered materials easily.

The weathered debris in deserts is moved by not only wind but also by rain/sheet wash. While wind moves fine materials, general mass erosion is accomplished mainly through sheet floods or sheet wash. Stream channels in desert areas are broad, smooth and indefinite and flow for a brief time after rains.

Thus, running water plays a dominant role in shaping landforms across both climatic regions through erosion and deposition.