Question

why is it impossible to define the boundary between humid climates and dry climates by a single precipitation amount?

Answer 1

The inability to define the boundary between humid and dry climates by a single precipitation amount is due to variations in evaporation rates, elevation differences, geographic features like mountain ranges that cause the rain shadow effect, and proximity to bodies of water. These complexities prevent a universal threshold from being applied.

Step-by-step explanation:

It is impossible to define the boundary between humid climates and dry climates by a single precipitation amount due to several factors that affect precipitation and evaporation.

In cooler climates, low precipitation does not always result in dry conditions because the evaporation rate is lower. Conversely, in warmer climates, the same amount of precipitation might lead to drier conditions due to higher evaporation rates.

Elevation, proximity to oceans, and geographic features like mountain ranges can also cause variations in precipitation patterns.

For example, the rain shadow effect describes how mountains can block precipitation, creating arid conditions on the leeward side despite higher precipitation on the windward side. These complexities make it difficult to set a universally applicable threshold of precipitation to delineate humid from dry climates.

Answer 2

Dryness is not only related to annual precipitation totals, but is also a function of evaporation. Dry climates have much lower rates of weathering than humid climates.