Assessment of temperature anomalies between present time and cold periods of Plio-Pleistocene using geomorphic indicators (case study: Kazab-Yazd)

Climate changes and remained geomorphic evidences due to the changes has been interested by geomorphologists in the world. Different researches have shown that world climate has been changed successively in Pleistocene so that with decreasing in temperature and probably increasing in precipitation, glaciers has been progressed and with increasing in temperature and decreasing in precipitation, they has been retreated. Because climate changes in the period has changed the surfaces of the earth, identifying and tracking the effect of the changes is very important in the understanding of environmental conditions during this period. One of the most important evidence of climate changes in Quaternary is remained landforms of glaciers. Although climate change is a global phenomenon, but the trend and the value of these changes varies in different regions of the world. So, the study of these changes should pay attention to in a local scales. Therefore. The main goal of the research is assessment of climate condition in Kazab Basin in the past and calculating differences temperature and precipitation between past and present time. Kazab Basin has located in the South-west Yazd city in the west of Shirkuh Mountain along 31°
52´  to 32° 7´  of northern latitudes and 53° 52´  to 54° 7´  of eastern longitudes. The range of elevation in the region is between 1732 meters in the output point of the basin and 2916 meters in the peaks of mountains. The area of the region is about 47 square Km. Primary studding show some landform which has created by glaciers such as cirques, U form valleys, and erratic stones. In the researches, we have tried to reconstruct past climate condition according to the landforms as indicators The research is based on field observations which according to geomorphic evidences remained from the past, we have studied morphoclimatic condition in the Pleistocene period. For reconstructing past climate condition in the research, we used many data such as topographical and geological map, aerial photographs, satellite images, Google Earth and DTM maps with resolution 20 meters, and also some software like GIS, Excel and GPS system. In addition, for studding present climate and comparing it with the past, we used temperature and precipitation data of 8 stations of rain gauge, 3 station of climatology, and 3 station of synoptic in the region and its surrounding. At first, using topographical maps and according to the form of contours, aerial photographs, satellite images as well as field studying, we marked glacier cirques. For drawing the maps of present isotherm, we create the correlation between altitudes and annual temperature amongst surrounding stations the region. Then, using altitude points extracted from DEM we provided isotherm map for present time. Furthermore, for drawing past isotherm and map, we calculated zero C. line (snowline) for the past with Wright and Porter methods. Then, we obtained an equation according to the correlation between altitude and temperature, and based on that, we evaluated adiabatic lapse rate. Using permanent snowline altitude and adiabatic lapse rate it would be draw past isotherm map. In the research, remained geomorphic indicators has been studied at first. Those which can help to understand and reconstruct Pleistocene paleoclimatic in the central of Iran. Therefore, permanent snow line was determined. The line has located at the height about 2274 meters on the basis of wright method and at height about 2200 meters according to Porter method. The line accepted as the border of temperature of zero degree in the past. Also, on the basis of erratic stones in the region was determined the equilibrium line of water and ice in the past. Findings show that the temperature in the region has decreased so that the minimum temperature in high altitude has reached to – 4,4 C.. Therefore, glacier’s tongue has been descended to about 1750 meters and there has been melt; because temperature in the altitude has increased to 3.2° C. The remained erratic stones in the altitude affirm the hypothesis. Therefore, with comparison of isotherm map of the region for present and past time, we estimated about 12, 4° C. changes in the temperature in the region. Also, different temperature show that lapse rate has been about 0.8° C. in the past, but it is about 0.65 at now. Probably, Siberian high pressure has dominated in the region during more often the months of the year. Results show great changes in climate in the region so that with field studding we observed many glacier landforms in the region such as a few cirques, U form valleys, stone traces as well as erratic stones. In according to these landforms as indicators for calculating climate changes, we tried to reconstruct climate condition in the past. Thus, we drew isotherm and isohyet maps for past and present time and compared them together using GIS. Results show that the temperature has been colder than now about 12,4° C.  Besides, the area of the glaciers has been spread to about 2200 meters (permanent snowline). But, glacier’s tongue has been descended to about 1600 meters inside the plain, and there has been melt; because temperature in the altitude increased to 4.1° C. the remained erratic in the region affirm the hypothesis.