The Late Quaternary Environmental changes in Iran

The history of The Quaternary evolution in Iran, is one of the important issues that have attracted theattention of many researchers over the past decades an. Despite many studies on the nature of thesechanges, and the existence evidences of these changes in the glacial and partly Holocene periods in Iran,there are still many uncertainties about it. There are two main views about the Pleistocene climate in Iran,the First, not only does not accept an increase in precipitation during the glacial periods, but also believesin its reduction from the present values. The second view that believed to increase the precipitation on theinner frontier of the Iranian plateau and the highlands. Proponents of the second theory also are twogroups. The first group, such as Scharlau, gives rise to a significant increase in rainfall and the other groupslight increases (Ayvazi ۲۰۱۳). This study, based on the hypothesis that the conditions in Iran were coldand dry during glacial periods, according to the detailed researches carried out in Iran over the past fewdecades, as well as in the sub-Saharan Africa, Arabia and Mesopotamia in the Quaternary, intends to finda response for the origins of rainy periods comparatively. We using the significant studies that have beencarried out over the past decades in relation to the Quaternary and in particular the late Quaternary changesin Iran, and distant areas, including the sub-Saharan Africa, the Arabian Peninsula, Oman andMesopotamia. using the technique of comparison and reviewing existing theories and resources, includingnumerous books and articles, and establishing a reasonable relationship between the events in Iran andother geographic regions during the late Quaternary (Pleistocene-Holocene transition).an attempt has beenmade to identify the general framework of changes during glacial and interglacial periods in the Iran. Aswell as, while paying special attention to the humid conditions of the first half of the Holocene in differentregions, including Iran, the possibility of occurrence of periods known as rainy periods or Iran's fluvialconditions in Holocene or in general in interglacial periods is discussed. In general, the geomorphicevidences, palynological data, climatic models, and archaeological data related to Iran and adjacentterritories, indicate that during the last glacial period, Iran has had colder and drier conditions than today.Based on the evidences, the Indian monsoon since the beginning of Holocene, except for limited areas inthe northeast, north, northwest, and parts of the west, has affected the country. In the first half of theHolocene, the monsoonal effects during summer, along with the influx of western low pressures in the coldseason, led to a very humid condition, especially in the central, eastern, southern and southwestern regionsof Iran throughout the year. Thus, the so-called rainy periods or fluvial periods in Iran, which its differentevidences have been documented, especially in the central regions, caused by these climatic systems.

Keywords:

Late Quaternary) , Iran , rainy periods