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Showing 23 results for Precipitation
Dr Alireza Shakiba, Dr Neda Esfandiari,
Volume 24, Issue 85 (3-2024)
Abstract
Atmospheric rivers (ARs) are integrated and concentrated moisture paths that can influence precipitation in different countries. In this research, we aim to quantify the spatial distribution of ARs for 147 synoptic stations in Iran, their precipitation contributions, and their relation to total precipitation for six cold months of the year for 25 years (1995-2020). In this regard, the atmospheric rivers were identified based on the geographical location of each station and its precipitation characteristics. Then statistical analysis was used to determine the precipitation share and spatial distribution. As a result, on average, 8% of all studied times are associated with atmospheric rivers throughout the country. In addition, approximately 51% of the events identified have resulted in precipitation. In terms of location, most of the stations on the western slopes of Zagros and some coastal stations in the south have experienced all these events as rainy. This phenomenon is estimated to have provided between 6 and 69 percent of the country's total rainfall during six months of cold weather. There is a maximum share of this in the country's southern regions, and this share has decreased with the increase in latitude. Furthermore, the rise in AR precipitation is associated with an increase in total monthly rainfall in 84% of the studied stations. There is a spatial dissimilarity in the rain-affected by the phenomenon at different times.
Dr Taghi Tavousi,
Volume 24, Issue 87 (10-2024)
Abstract
Introduction
Extreme phenomena such as heavy rainfall is one of the most important climatic parameters in any geographical area. Rainfall is one of the appropriate climatic parameters in estimating potential impacts of climate change in the environment and in many economic and social systems. The Precipitation enhances runoff and providing soil moisture. Heavy rainfall increases runoff and leads to flooding. This climate parameter in arid areas such as southeastern Iran has wide variations. There is a direct relationship between rainfall and the activity of precipitation systems in South East of Iran. Some researches show that during half a century synoptic patterns by more and severe raining events and by changes in scheduling and rain status has been changed. From 1960s, the abundance and severity of extreme rainfalls throughout the world has increased and it is expected to continue the increase until the end of the current century. So understanding the behavior of extreme events is one of the main aspects of climate changes. The increase information about heavy rainfalls has importance for society, especially for the population who lives in areas with increased flood risk.
Among heavy rainfall characteristics, the portion of such extreme precipitations is studied less. Due to the experiments carried out, the increase of annual rainfall in southeastern Iran happens through extreme precipitations. Therefore extreme precipitations portions out of total annual rainfalls can be defined as an index of crisis. The increase of this index implies the extreme floods in rainy years and severe drought and drought years. According to abnormal behavior and irregular extreme precipitations in south east of Iran and its high variability and arid regions ability to heaviness and extension of Heavy Rainfalls, the necessity of understanding and Analysis of synoptic patterns affecting heavy rainfall in the low rainfall region of southeastern Iran is recognized.
Materials and Methods
The purpose of this study is to analyze extreme precipitations in South East of Iran. First, the southeastern corner of Iran was selected from latitude 34 ° N and Longitude 53 ° E. The daily precipitation data during the period (1951-2020) of meteorological stations in the study area (in Sistan and Baluchestan, South Khorasan, Kerman, Hormozgan, Fars and Yazd provinces) were obtained. Then, the standardized data matrix was set up in MATLAB software, which the length, width and the number of days it represents the precipitation statistics of the stations. On this matrix, the cluster analysis was performed using the Euclidean Distance and Ward Linkage methods. To understand the role of dynamic and thermodynamic factors in the occurrence of these rainfall, were used the geo potential Height, sea level pressure, air temperature, specific humidity, zonal and meridional wind components in latitudes 0 to 80 degrees north and Longitude of 0 to 120 degrees east that was related to 6-hour rainfall and maps with dimensions of 2.5 × 2.5 degrees, the were interpolated by using the Kriging method.
Results and Discussion
The heavy rainfall always have been one of the hazards of climate that the destruction and irreparable damages life and property is involved. Therefore, understanding the factors and parameters that create the climate system precipitation in any place and at any time of the year is necessary.
Rainfall phenomenon is very complex and nonlinear that the great variability over time and space and a variety of conditions that have important role in the occurrence can be divided into two categories: Synoptic Patterns and local conditions.
Weather is largely controlled by the passage of Synoptic Patterns. On the other hand the occurrence of any weather's particular pattern is to a large extend determined by the distributions of land masses, sea surface temperature gradients,Characteristics and type of land cover (biosphere), topography and the orientation of baroclinic zones.
Conclusion
In this study, synoptic patterns affecting heavy rainfall in the low rainfall region of southeastern Iran has been analyzed using environmental to circulation approach. The results showed different patterns of heavy rainfall. When a low polar pressure with Sudan's low pressure is encountered, severe Baroclinicity conditions arise in the direction of northwest, southeast is associated whit the trough located in East Black Sea - East Mediterranean which Iran has been in the East of this synoptic system where Positive vorticity occurs. Analysis of synoptic patterns affecting heavy rainfall in the low rainfall region of southeastern Iran showed that the main reason of these rainfalls had been the siberian and Black Sea unticyclones, troughs of Red Sea and Persian Gulf.
In the summer, synoptic patterns of seasonal rains in South East of Iran often Due of the spread of monsoon air mass. In winter, westerly winds extend towards lower latitudes including the study area, the seasonal rainfall pattern in the region brings.
Dr Mostafa Karampoor, Miss Samira Beyranvand, Dr Massoud Goodarzi, Dr Azar Beyranvand,
Volume 24, Issue 88 (1-2025)
Abstract
The occurrence of climatic extremes such as heat waves, heavy rains and droughts cause significant damage to human societies. Analyzing the change in the frequency of these phenomena and examining the trend and intensity of the observed events and the predicted events can help significantly in planning to manage and adapt to these events. In the current research, the effects of climate change on the drought situation of Lorestan province have been evaluated using the Standardized Precipitation Drought Index (SPI) and then the trend of this index was investigated. Since the computational grids of the atmospheric general circulation model (GCM) must be downscaling in the dimensions of one station due to their large scale and low resolution for use, so at first the daily output data of the atmospheric general circulation model HADCM3 under the release scenario A2 and B1, downscaling by the LARS-WG version 5 statistical model and the ability of the LARS-WG5 model in simulating the past climate (1996-2011) in the synoptic stations of Aliguderz, Khorramabad and Borujerd has been verified, then the precipitation gauge for The period 2011-2050 has been simulated for the studied stations. The results obtained from the study of the drought trend indicate the intensification of droughts in the winter season during the coming decades in Aliguderz and Borujerd stations and the weakening of droughts in Khorramabad station. The spring season shows a weakening of the drought in all three studied stations except the INCM3 model, where Aliguderz and Khorramabad stations have significant trends under the HADCM3 model under scenario A2 and the INCM3 model under scenario A2 and B1, respectively. In order to adapt the agricultural sector to these changes, an adaptive capacity strategy should be adopted in the agricultural management and planning department of this province to plan the time and type of cultivation by considering these changes. Also, take action in the direction of better productivity.
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