فصلنامه جغرافیای طبیعی
پیاپی 50 (زمستان 1399)

Heavy rains often lead to destructive floods, so discovering the prevailing pattern any climate system will allow for optimal analysis and forecasting. The present study was conducted to explain the synoptic of heavy rainfall leading to floods on 22 January 2020 in southern Sistan and Baluchestan province. Maps of different levels of the atmosphere were analyzed before a day the flood. In order to accomplish this, the required data have been extracted from NCEP/NCAR affiliated with the National Organization of the Oceanography of the United States. In the next step, the geo-potential height, vorticity, omega, wind direction, wind speed, specific humidity, Moisture Flux Convergence maps and Hoff Miller diagram was drawn and analyzed. The results showed that settle of trough vorticity in Saudi Arabia zone in the middle of the atmosphere along with the jet core at the upper levels provided favorable conditions for unstable weather and ascent in the southeastern region of Iran, so that the omega reached 0.45 Pascal per second. Special humidity maps also showed that at the same time as the settle of trough vorticity in region, considerable moisture flowed from the Arabian Sea and the Persian Gulf to southeastern Iran. Therefore, rapid conversion of atmospheric moisture to precipitation in trough vorticity has been the main cause of heavy rainfall on the above day.

The abnormalities and the occurrence of climate hazards, the importance of the phenomenon of climate change is becoming increasingly apparent. Changes in air temperature and precipitation play a significant role in detecting the effects of climate change. In this study, the perspective of changes in air temperature and precipitation in Kohgiluyeh and Boyer-Ahmad provinces was evaluated with a statistical approach. In this regard, the statistics of weather stations in the period (1986-2015) was used as the base period. For future period, the output of the MIROC5 as general circulation model (GCM) under RCP8.5 and RCP4.5 scenarios in the form of downscaled data from the MarksimGCM database was used. Results of projecting the future period in the form of high and medium radiative forcing scenarios (RCP) shows an upward trend in the minimum and maximum temperatures of the study area in the future period compared to the base period. This incremental deviation is greater in the decades relative to the present period. Spatially to the time horizon 2061; areas with cooler and warmer temperatures will be added in the province. From the low altitudes or southern part of the province, with the passage to the following decades, the range of milder and warmer temperatures will gradually increase compared to the base period. The Precipitation parameters in the coming period will face a sharp and significant decrease compared to the base period, especially in the wet months of the year. This rainy region of high Zagros range,will face a significant decrease in rainfall in the coming period.

Climate is the most important factor that determines the type of crop to planting in each region. Due to the fact that the cultivation of dryland wheat is a priority in the province, this study was selected. In this study, climatic data of 6 synoptic stations (1989-2012) and 8 climatology stations (2008-2013) were used. Due to the date of the beginning of autumn rains, planting date was suggested for each region of the province. Then different types of probabilistic distributions were fitted to the planting date. The best statistical distribution was selected from the coefficient of determination and different growth stages of dryland wheat were determined. From the precipitation element, the required types of precipitation maps were extracted. Also from the temperature element, various temperature maps and temperature stresses were prepared. Finally, climatic zoning map of dry land wheat were extracted and from this map the areas with no potential of cultivation were omitted. The final map comprised four very good, good, medium and weak areas. And maps of zoning for 5 mm Precipitation revealed that very suitable area for cultivation of wheat was located in some parts of the Northwest, West and South west of Kermanshah province. And suitable areas, was in the Northwest, West, Southwest and medium areas was located in Southwest, West,Center, North, Northeast, and southeast, And weak areas are often located in center and northeast.

Iran's location on the arid and semi-arid belt of the world, as well as the mismanagement of water resources, has created a warning situation of water shortage in many parts of the country. The present research evaluates the effects of climate change on temperature, rainfall and runoff in future periods with the help of LARS-WG statistical model and SWAT hydrological conceptual model for Lar Basin. To estimate the flow rate of the river, the performance of Bayesian network and the combined wavelet-neural network model are also examined. After entering the rainfall and temperature information of the region, runoff was simulated for two hydrometric stations of Gozeldareh and Plour and the outflow runoff of Plour station between 1979 to 2018 was calibrated and validated as a control point. In order to evaluate the efficiency of the models, the criteria of Nash-Sutcliffe and explanation coefficient are used. According to climate models, the highest temperature increase in the final period and under the RCP8.5 climate scenario shows about 10% increase in temperature in spring and winter. Finally, among these models, the physical model with an average annual prediction of 6.04 cubic meters per second according to the observation period, showed a decrease in runoff

The preparation of geomorphological maps is requiring a lot of time and extensive money to collect information on maternal and landforms. Registration maternal features in these maps are usually based on geological maps, field operations, and aerial photographs analyzing. However, due to the resistance of rocks and sediments against erosion is different, it is possible to identify and distinguish them by 1:25000 topographic maps and by studying the form of contours. The purpose of this study is to identify contour forms of topographic maps and find their relationship with geological formations of the region in Part of northern and southern Alborz. For this purpose, the existing contours forms including straight contours, and simple sinusoidal, long and elongated sinusoidal, dense sinusoidal and pulsed curves are classified in topography maps of the region and overlapped with the formation maps of the region that supply by using geological maps 1:100000 geological surveys of Iran. Chi-square tests were used to analyze the relationship between them. The results showed that the contour forms of the geological formations of the area were significantly different at the 0.01 level. The contour forms of straight and simple predominate in hard rocks and dense sinusoidal forms in loose formations and are higher than expected. Therefore, the rock material is effective in creating specific contour forms of topographic maps of the area and since these forms are easily recognizable in these maps, it is therefore possible to use topographic maps to obtain material information for geomorphological maps.

Flooding is a phenomenon that most climatic regions experience. Floods often cause problems such as; Soil erosion, sediment accumulation and loss of life and property. Therefore, flood climatology plays an important role in reducing and preventing possible environmental damage. For study the synoptic climatology of floods in Aras river basin, daily data of 9 hydrometric stations and 6 synoptic stations during 1979-2014 have been used. Data on geopotential elevation, sea level pressure, specific humidity, omega index and Zonal (Meridional) wind components were also obtained from the US National Centers for Environmental Prediction/ Atmospheric Research. After reviewing the monthly and seasonal regime of the river and identifying the flood days, severe floods with discharge more than 700 m3/s in Khodaafarin hydrometer station were determined. In order to analyze the synoptic patterns of severe floods in Aras basin from the indicators; Moisture flux convergence function, fronting function and divergence function have been used. The results showed that during 4 severe floods in the region some atmospheric phenomena such as; a deep trough on the Black Sea, the Red Sea and the Persian Gulf and a cut off low on the west of the Caspian Sea at 500 hPa level in the region has been formed. At sea level, the formation of high pressure on the Caspian Sea and low pressure on Iraq and western Iran has caused the pattern of pressure changes in the region to increase and provide conditions for climbing. Applying the moisture flux convergence function showed that the source of moisture for these floods was mainly the Caspian Sea.

Flood is one of the most important and accident-prone natural hazards in Iran. Identifying flood areas and flood spreading is a key step in flood risk management, and flood risk zoning provides a small measurement of flood risk, so it is possible to send appropriate alerts in the event of a flood risk and facilitate rescue operations. The downstream potential of Ardabil city basin helps to nourish the artificial environment of the basin and also increases the quality of environmental lands. The purpose of this study is to identify areas prone to flooding and flood spread in case of flood crisis. All processes and data analysis in ARC GIS environment using electron method and Boolean logic to weight and integrate layers such as (slope, erosion, land use, waterway network, soil, geology, land curvature, Quaternary unit, groundwater level, density Vegetation, runoff and soil moisture) were used and susceptible areas were identified when exposed to danger. The results showed that areas with high flood intensity have characteristics such as alluvial and convex sediments at the foot of steep slopes and watersheds with rock outcrops. The presence of fan-shaped alluvium and alluvial fans at the outlets of canals and waterways with mountainous watersheds and hills leading to low-lying plains is the presence of low-lying lands in relation to the surrounding lands. The final result of the analysis, both in the electrode method and in the overlap, gives the information that the central part is more at risk of flooding than the Samarin and Hir parts.