Understanding natural issues and the way natural phenomena operate, whether in order to enjoy their benefits or to deal with their adverse effects, must be accompanied by observation and interpretation of phenomena. Proper interpretation and accurate analysis of the results of observations requires necessary and sufficient information concerning the events’ ways of occurring and the past history of phenomena. In natural problems such as landslides, earthquakes, etc., and in historical issues and requirements of humans such as nutrition, habitation, water pollution, etc., the instantaneous recognition or the course of changes in time as well as historical comparison of magnitude of changes are duly considered, and geographers can well examine this issue and consider, in their studies on large expanses of land, how short-term changes occur during the phenomenon, and, by referring to these changes, generalize the results to the future and predict the intensity and extent of future events. Thus it can be said that natural geography perceives the momentary balance of phenomena, or at least seeks to understand it, and even takes time backward or forward on a scale of human history.
 In other words, the present form of the Earth and the current conditions in any given phenomenon are of great concern to geographers, but accurate information from the past is always needed for their accurate examination. Furthermore, there is a need for predictions about the future trend based on current trends and past information when considering long-term exploitation of natural resources. According to the above-mentioned matters, it can be clearly stated that the study of changes in phenomena over time is the basis of geography studies, especially natural geography. Fortunately, today with the development of communications, it is possible to extend the scope of these studies to different spaces with various features, and also to collect more information; on the other hand, using new methods, techniques and facilities, the horizons of vision in the past, and in some cases in the future, have become more extensive.