Abstract
In the Holocene, there has been a sudden and severe climate change that has affected the process of cultural evolution, subsistence system, demographic change, and the pattern of the distribution of human settlements. Palaeoclimatological studies show that in the second half of the 7th millennium BC, during a cold and dry climatic event, with a peak of about 6200 BC, the settlement conditions, in particular in some parts of the Northern hemisphere, were significantly disturbed. After this period, the air temperature rose sharply and replaced the warm and dry climate from the beginning of the 6th millennium BC. From the second quarter of the 6th millennium BC, gradually, the amount of humidity increased and the air temperature decreased, so that from the beginning of the second half of the 6th millennium BC, more favorable climate conditions were created for agricultural activities. The early evidence of the human settlements in the North of Central Iran region mainly belongs to the beginning of the sixth millennium BC. Due to the lack of architectural evidence from the first half of the 6th millennium BC in this region, human societies were probably semi-sedentary. From about 5400 BC, sedentary-farmer settlements with architecture were established and gradually their number increased. In the early 5th millennium BC, a warm and dry climatic change caused the interregnum/collapse of the settlements in the region. Therefore, the time of the genesis and prosperity of the early settlements in the North of Central Iran was related to the climatic conditions and occurred in an appropriate climate period between two dry periods.
Keywords: The Mid-Holocene, Climate Change, 6200 BC Event, 6th Millennium BC, The North of Central Iran.

Introduction
Although human beings have the liberty in nature, the study of the cultural evolution of human societies without reference to environmental change cannot be valid. In other words, one of the main motives of cultural dynamism and evolution is interactions between humans and the environment.
The Holocene period is divided into three phases: the early Holocene (ca. 9700 - 6000 BC), the middle (ca. 6000-3000 BC) and the late (ca. 3000 BC). Abrupt climate changes, both warming and colding, which have led to drought and unfavorable environmental conditions, have repeatedly occurred since the beginning of the Holocene age and have led to cultural collapses in human societies. However, between these climatic events, we often witness the birth of a new or evolved culture.
In the cultural region of the North of Central Iran, with the exception of the Western Tepe of Sang-i Chakhmaq, no evidence has yet been found of human settlements belonging to before the sixth millennium BC (the beginning of the Middle Holocene). Due to the occurrence of the 6200 BC climatic event, which caused a severe cold-drought period for 200-400 years (in different regions), presumably, the lack of prehistoric sites has been linked to unfavorable climatic conditions in this arid and semi-arid cultural region. The results of palaeoclimatological studies, together with absolute datings, can not only be useful in more accurate chronology of ancient sites, but also they can explain the causes of population changes, settlement patterns, many of migrations and displacements of human societies, as well as changes in their diet and lifestyle. In this study, considering the climatic condition of the early Mid-Holocene, based on the palaeoclimatological studies carried out in several sites, the initial status of human settlements in the North of Central Iran region during the sixth millennium BC will be discussed.

Research Findings
In the Holocene, the air temperature and moisture significantly increased compared to the Ice Age, and the changing climate led to the emergence of the Neolithic Age and food production. However, during this period, despite the high average of the air temperature, the earth experienced severe climate changes, which affected cultural development, demographic changes, subsistence system, and the distribution pattern of human settlements. Around 6200 BC, suddenly, a very cold climate change occurred, which lasted 150 to 600 years in different regions. The occurrence of this event led to changes in the lifestyle of the Neolithic communities. The cultural region of the North of Central Iran consists of two parts: the Western part (the salt lake basin) and the Eastern part (the Western half of the central desert basin). The oldest Neolithic settlement in the Western part of the region is the Western tepe of Sang-i Chakhmaq dating back to 7200 BC to 6600 BC, but in the Eastern part, no settlements belonging to before 6100 BC have been found.
So far, a few semi-sedentary sites belonging to the first half of the 6th millennium BC in the salt lake basin have been identified. Palaeoclimatological studies show that the air temperature and humidity have suddenly increased sharply after the 6200 BC cold event. However, since the second quarter of the 6th millennium BC, the air temperature has gradually decreased. In the middle of this millennium, an abrupt warming fluctuation occurred, but from about 5400 BC, the air temperature and humidity reached an optimum level for agricultural activities. In general, the early sedentary-farmer settlements in this region belong to after 5400 BC. However, at the end of the 6th millennium BC, another climate change caused severe warm-dry conditions, in which, since the beginning of the fifth millennium BC, settlements gradually collapsed.

Conclusion
The cultural area of North Central Iran consists of two parts: West (catchment basin of Namak Lake) and East (Western half catchment basin of central desert). The first Neolithic settlement in the Western part of this region, Western mound of Sang-i Chakhmaq with dating 7200 BC to 6600 BC. In the eastern part, so far, no settlement older haven’t been found than 6100 BC. The early sedentary-farmer settlements in the cultural region of the north of central Iran, such as Yan Tepe of the Ozbeki site, Tepe Ibrahim Abad, Tepe Moein Abad, Northern Tepe of the Sialk site, Tepe Pardis and Tepe Cheshmeh Ali, have been established and developed in a 400-year period between 5400 and 5000 BC with a relatively mild and humid climate, between two severe drought periods.

Abstract
The potential vulnerability of primitive societies to natural disasters, such as droughts, floods, and famines caused by climate change, is an important issue that requires careful study. The main aim of this research is to investigate the possible effects of ancient environmental and climatic changes on Bronze Age settlements in southeastern Iran, as well as the main dynasties that ruled Iran based on archaeological and historical evidence of territorial boundaries, economic and political prosperity. Adaptation of climatic and cultural changes in the southeast of Iran can provide valuable information for researchers. In this regard, this article aims to answer the question of whether climate change has affected the ancient societies of Jiroft, and to what extent climate change has affected the economic prosperity and political influence of the ruling dynasties that have affected Iran. In the present study, using a combination of geochemical and pollinological indicators, we examine paleoclimatic changes of the southeastern plateau of Iran during the past 4000 years. Significant agricultural activities existed between 3900 and 3700 years ago in the southeast of Iran during moderate climatic conditions. Dry conditions with increased dust prevailed over the region from 3300 to 2900 years ago. Wet conditions from about 2900 to 2300 years ago facilitated extensive agriculture and coincided with the flourishing of regional governments such as the Medes, Urartos, and Mannas in the western Iran, and after that the Achaemenid Empire throughout Greater Iran. The decline of the Achaemenid Empire coincided with the beginning of a dry period that made agriculture less prosperous in Jiroft for nearly 200 years. Southeast Iran experienced humid conditions between 1550 and 1300 years ago, which coincided with the economic prosperity of the middle to late Sassanid Empire.
Keywords: Climate change, Sassanid, Bronze Age, Sediment core, Achaemenids.

Introduction
This study aims to reconstruct the paleoclimate history in southeastern Iran by tracing the landscape changes and climate fluctuations since the Late Bronze Age and their impacts on human societies based on palaeo-environmental analysis of a wetland system. It will further evaluate the possible impacts of climate change on major ruling dynasties of Iran since the Late Bronze Age. An example of the latter would be following the territorial extent of major ruling dynasties from historical records, which would have been quintessential to society’s prosperity and growth coeval to favorable climatic conditions for agriculture and trade, and the development of city-states. The study involves a multi-proxy palaeo-environmental reconstruction using geochemical, and paleoecological proxies in a 250-cm long peat sequence near the archaeological complex at Konar Sandal near Jiroft, covering the last 4000 cal yr BP. The different proxies suggest changes in elemental concentrations, stable isotopes, and pollen records. 

Materials and methods
Palynological analysis were done in Thirty-five subsamples at intervals of 1-10 cm at the Institut Méditerranéen de Biodiversité et d’Ecologie, Aix-en-Provence, France by procedure described by Gurjazkaite et al. (2018). 

Geographical setting
Konar Sandal (25 km south of Jiroft in southeast Iran) is the main excavation site in the Jiroft Valley. Several high mountain chains surround it, some of them rising to 3700 m asl (Fig. 1). The Halil Rud stretches from north to southeast for almost 400 km through fertile agricultural land before draining into the Jazmurian playa south of Konar Sandal. The water level in the river fluctuates throughout the year.

Results
The sediment core was divided into six major units based on the sedimentological, geochemical, and palynological characteristics (Fig 2 and Fig. 3). The elemental ratios (Si/Al, Ti/Al, and Fe/Al) had relatively low values in Unit 1 (U 1; 250-189 cm; 4011-3548 cal yr BP). The first significant appearance of Cerealia-type pollen occurred in this unit extending from 3880-3700 cal yr BP (230-207 cm). The δ13COM showed a distinct increase in Unit 2 (U 2; 189-164 cm; 3548-3293 cal yr BP). Unit 3 (U 3; 164-134 cm; 3293-2897 cal yr BP) was characterized by high elemental ratios (Si/Al, Ti/Al, and Fe/Al). The K/Ti ratio had the highest values in the entire core in Unit 4 (U 4; 134-106 cm; 2897-2302 cal yr BP). δ13COM values were more negative in Unit 5 (U 5; 106-61 cm; 2302-1540 cal yr BP). Unit 6 (U 6; 61-10 cm; 1540-854 cal yr BP) was characterized by moderate values of different elemental ratios. 


Discussion
Around 3950 cal yr BP a wet period prevailed based on elemental ratios, stable C isotope, and pollen (Fig. 3). Between 3900 and 3300 cal yr BP, mild climate conditions developed. significant appearance of Cerealia-type pollen and agricultural activities existed between 3900 and 3700 cal yr BP. Dry and windy conditions followed from ca. 3300-2900 cal yr BP with the driest conditions around 3200 cal yr BP coinciding with the regional Late Bronze Age cultural collapse. The driest conditions in this dry period occurred around 3200 cal yr BP, coinciding with the decline of the Jiraft Bronze Age civilization at the end of the Bronze Age. The long wet period extending from 2900 to 2300 cal yr BP with a high presence of Sparganium-type and intensive agricultural practices. Wet conditions in the Jiroft valley from about during this period, simultaneously with the flourishing of the powerful Medes and Achaemenid empires, facilitated extensive agriculture. The decline of the Achaemenid Empire coincided with the beginning of a dry period that made agriculture less prosperous in Jiroft Valley for nearly 200 years. The highest Ti/Al values coeval with the lowest δ13COM values suggest an increase in Aeolian activity and dry conditions between 2100 and 1650 cal yr BP. The Jiroft Valley once again experienced humid conditions between 1550 and 1300 cal yr BP, which coincides with the economic prosperity of the mid to late Sassanid Empire (Fig. 4). 

Conclusion
In the present study, using a combination of geochemical and pollinological indicators, we examine the paleo-environmental changes of the ancient Jiroft valley in the southeast of Iran during the past 4000 years and their possible effects on the settlements of the Bronze Age and the main dynasties that ruled Iran based on records. 
The Jiroft Valley experienced wet conditions between 1550 and 1300 cal yr BP, which overlapped with one of the most extensive territorial boundaries in Iran’s imperial history (the Sassanid Empire in the early 7th century C.E.). Although mild conditions prevailed between 1315 and 854 cal yr BP, agricultural activities declined, probably due to weak succession and political instability. We evaluate the archeology and history of territorial borders, economic and political prosperity. Paleo-environmental reconstruction shows that the wet periods and increased agriculture in the Jiroft Valley coincided with the peak of political influence and economic wealth of the Achaemenid and Sassanid empires. Therefore, more detailed paleoclimatic records would be helpful for investigating the interplay of political and climatic factors in the development and decline of ancient settlements and imperial powers in Eurasian history.