Physical Geography as a science is experiencing a radical change in philosophy. It is changing from a science that was highly descriptive to one that is increasingly experimental and theoretical. This transition represents a strong desire by Physical Geographers to understand the processes that cause the patterns or forms we see in nature.
Before 1950, the main purpose of research in Physical Geography was the description of the natural phenomena. Much of this description involved measurement for the purpose of gaining basic facts dealing with form or spatial appearance. Out of this research Physical Geographers determined such things as: the climatic characteristics for specific locations and regions of the planet; flow rates of rivers; soil characteristics for various locations on the Earth's surface; distribution ranges of plant and animal species; and calculations of the amount of freshwater stored in lakes, glaciers, rivers and the atmosphere. By the beginning of the 20th century Physical Geographers began to examine the descriptive data that was collected, and started to ask questions related to why? Why is the climate of urban environments different from the climate of rural? Why does hail only form in thunderstorms? Why are soils of the world's tropical regions nutrient poor? Why do humid and arid regions of the world experience different levels of erosion?
In Physical Geography, and all other sciences, most questions that deal with why are usually queries about process. Some level of understanding about process can be derived from basic descriptive data. Process is best studied, however, through experimental manipulation and hypothesis testing. By 1950, Physical Geographers were more interested in figuring out process than just collecting descriptive facts about the world. This attitude is even more prevalent today because of our growing need to understand how humans are changing the Earth and its environment.
Finally, as mentioned above, a deeper understanding of process normally requires the use of hypothesis testing, experimental methods, and statistics. As a result, the standard undergraduate and graduate curriculum in Physical Geography exposes students to this type of knowledge so they can better ask the question why?