In order to understand the pressure patterns cauaing the summer monsoon rains in the south east of Iran, daily values of pressure and wind components of 500, 700, and 850 hectopascal levels and sea level were obtained from NCEP site and daily rain data of 152 stations of Iran were provided by the Islamic Republic of Iran Meteorological Organization for 1970-2003 period. Spatial analysis of the rain data showed that there is a triangular area in the southeast of the country located to the east of 58:30 E and south of 28:30 N which gets rain every summer. This area is called an index area of Monsoon rains in Iran. The temporal analysis of the monthly rainfall of this index area indicated the June 1994 as the highest and most widespread rainfall during the study period. This study analysed the synoptic patterns causing this intensive rainfall period through the different atmospheric levels at the daily to seasonal scales.The results showed that: The Subtropical High Pressure was stronger and expanded east ward over India at the higher levels. At the same time at the lower levels the monsoon depression was expanded west ward over Arabian Sea creating positive vorticity over the area and making it possible for the air to ascend. The tropical easterly cyclones intruded the southeast of Iran in July1994 more than the other similar months. The westerly trough was deepened over the west of Iran. The south-westerly winds of Arabian Sea and Bay of Bengal became stronger. All these patterns and configurations caused the expantion of Monsoon rains to Iran and as a result very intensive rain happened over the area.

Projection of summer monsoon rains in Southeast Iran based on Ensemble model the precipitation factor has a variable and random nature and has a different behavior in terms of space and time. Therefore, the prediction of precipitation has more uncertainty compared to other meteorological variables. In the current study, the data output of Cordex database and CMIP5 models were used using the neural network method to reduce the uncertainty and estimate precipitation properly. The results showed that due to the high correlation of temperature, humidity and air pressure with precipitation, the use of these variables is beneficial in reducing the uncertainty of precipitation forecast. In addition, the non-linear method of artificial neural networks can be used to bias the rainfall data of Cordex database and CMIP5 to forecast the rainfall in the southeast of the country. Another result of this research is the increasing trend of rainfall in the southeast of Iran, especially in the coastal areas. This can be considered as a result of the increase in the level under the influence of rains affected or simultaneous with the southwest monsoon of India. The increasing trend of precipitation in the southern coasts is also related to the increase in the storage capacity of moisture content. The interannual variability of India's monsoon rainfall also shows a steady positive trend under continued global warming. Since both the increase in the duration of monsoon rains and the increase in interannual variability in the future are seen in most models, we can be confident in these predicted trends. Indian summer monsoon rainfall is also predicted to be higher under global warming in the 2050s compared to the baseline.

To determine of location and type of blockings affecting the cold climate of Iran, daily geopotential height data of 500 hPa in 10-70 degrees north and 10-80 degrees east with grid point of 2.5 degrees in period of 1961-2010 were used. Blockings were identified by quantitative Tebaldi index on digital points. In the study area, there are three areas of blocking occurrence in Central Europe, Eastern Europe and Central Asia, respectively. The predominant type of blocking in these areas is of the Rex type, with the blocking and the cold storage being placed on top of each other in the middle levels of the atmosphere.  If a Rex block is formed in Central and Eastern Europe, at the same time, a deep or cold trough is formed in Central Asia, and this sequence is normal in meridional atmospheric systems. Iran's precipitation is most closely related to the Eastern European blocking system and the Central Asian cold zone, and precipitation is increasing in most parts of Iran. However, if atmospheric high increases in Central Asia and omega-type blocking is formed, due to the increase in atmospheric altitude, precipitation will decrease in most parts of Iran. But if an omega-type blockage is formed in Central Europe, with the deepening of trough in the Balkans and the Black Sea, it is accompanied by precipitation in northwestern Iran, and if this type of blocking is formed in Eastern Europe, the concentration of precipitation is mainly in the Caspian region, from the Eastern Caspian to the northeast of Iran.

Mechanism, spring rains, mainly due to convective processes, the occurrence of rains and other climatic phenomena, such as the phenomenon as cut-off low provides conditions for heavy precipitation events. In this research first heavy rains of spring (rains of 30 mm with the highest total precipitation in the period 1335-1391) studied the city and two of the strongest of them were identified. To analyze these rains, we investigate instability indexes and sea level pressure, 500 hPa, Uwind, Vwind, omega and data of cloud height (High Cloud Top, Middle Cloud Top, Low Cloud Top, High Cloud Bottom, Middle Cloud Bottom and Low Cloud Bottom). The result show that main factor of heavy rains in the region is trough of east Mediterranean in the middle troposphere cut-off low phenomenon is well established, Therefore in both cases west instability systems change their ways to lower latitude so that the west systems get high level of humidity from southern warm water and make heavy rains in the region is significant. Also results instability indexes show that there is instability probability, the amount Omega negative and positive vorticity show severe Ascending movement in time is the occurrence of precipitation; but with investigation relation within thickness of cloud and heavy rains show thickness of clouds have increased.

Heavy and torrential rains are one of the hazardous phenomena of atmosphere which always cause several severe damages over Iran. For this reason in every developmental program their intensity and frequency should be understood and predicted. The main factor to their development and intensification are the atmospheric pressure patterns and motions. Therefore, in order to predict their occurrence, in this study we extracted the highest daily precipitation of days with 90thpercentile and above of the year for the 40 selected stations during the 1980- 2009 period. Of these days we selected the days in which at least 25 percent of the stations had the highest daily precipitation. For the selected days we extracted the 500 hPa and sea level pressure maps. Then we clustered the sea level ...

In AquaCrop model was used to calibrate and verify the performance of the winter wheat crop in south of Iraq Al-Suwaira Research Station using data recorded in period 1/1/2008 and 31/12/2017. The results showed an increase in both annual and monsoon rains at the mid and end century periods for both RCP4.5 and REP8.5 scenarios implementing model GFDL-ESM2M. The annual and monsoon rains decreased in the EC-Earth model for both the RCP4.5 and RCP8.5 scenarios, while increased slightly in the CNRM-CM5 model under RCP4.5 and dropped with RCP8.5. Highest yield was recorded at the base period (2.36 ton/hectare) during the simulation period. The water productivity increased compared to the base period 2040-2050, while it was equal for both base period and the period 2020-2030 and in the RCP8.5 scenario.

Classifying daily climate circulation patterns has always been considered by climatologists. Investigating climate changes such as rainfall and the temperature in a same single time and place suggests that these changes are strongly influenced by atmospheric circulation patterns.Regarding so, climate changes, known as variables here, such as rainfall, temperature, and other related phenomena, which are exemplified as flood, drought, glacial, and etc. are associated with special types of climate circulation patterns. The continuity and alternation of the systems are classified or identified climatically, therefore weather classification system is one of the main objectives of the synoptic climatology (Huth, 1996). Since every weather type creates its own special environmental condition, lack of identification in weather type frequencies leads to a difficult environmental explanation and alternation (Alijani, 1380: 64)…..

In order to analyze the spatial characteristics of the daily hazardous temperatures and rains, the daily rain and temperature data were obtained from the Meteorological Organization of Iran for all of the long period stations for the existing period. Then the hazard indices were defined as: sultry days, cold days, Icy days, warm days, warm nights, extreme daily rainfall threshold, and percentage of extreme daily rainfall from the annual rainfall. These indices were annually averaged for each station. The results showed that every point of the country experiences some kind of climatic hazards. At least 40 percent of the year at each station experience hazardous climatic events. The spatial distribution of the indices varied from one kind to another. The sultry days were frequent in the south whereas the cold days are more in the north. The southern coasts experience more hazards than the northern coasts. Among the indices the warm days and heavy rains are very frequent all over the country. But the cold hazards are restricted to the mountainous and northern parts of the country. The results indicate that the planners and managers of the country should be prepared for the climatic hazards all over the country and take into consideration their existence.

The rain can be regarded as one of the most important natural resources, and human survival is largely dependent on it. If there was not about 31.536 km3 of rainfall on earth, the earth should have changed to an arid desert. However, today the rainfall has become a matter of danger in some parts of the world due to the advent of acid rains. For example, acid rains are seen around power plants, factories, and the like" because of the mixture of rain with pollutants in the air which in turn produces nitric and sulphuric acids. However, the impacts of acid rains are not limited to what mentioned above; they play essential role in the problem of environmental degradation in many areas of the world. This paper is a focus on the problem of acid rain and its production and impacts, through which some recommendations are finally being presented.

Introduction Cut-off  lows are cold -core cyclones in the upper troposphere that are identified as local minimums of geopotential elevation fields in the range of 500 and 200 hPa )Nito et al, 2008; Pinheiro et al, 2017; Muñoz et al, 2020(. Cut-off lows occur in most seasons, often in late winter and early spring. One of the synoptic patterns affecting temperature and precipitation as well as heavy rainfall in Iran is cut-off lows. This study has been compiled according to the importance and relationship between cut-off lows and heavy rainfall in the statistical period of 33 years (1986-2018). In this study, the climatology of cut-off lows systems at the level of 500 hPa of the northern hemisphere effective on heavy rainfall in Iran has been discussed. The ECMWF reanalysis data were used to identify and track cut-off lows that lasted for more than 48 hours in the statistical period of 33 years (1986-2018). For this purpose, geopotential, wind, and temperature data also were used.   Materials and Methods In this study, from the average daily data: Geopotential height, wind orbit, and temperature level of 500 hPa of the re-analyzed ECMWF European site with a grid step of 0.125 * 0.125 in the statistical period of 33 years (1986-2018) Used in areas including 0 to 80 degrees north latitude and 0 to 80 degrees east longitude. The Tibaldi-Multney index was used to identify Cut-Off low. And the Cut-Off lows that were effective in Iran's heavy rainfall were studied.   Results and Discussion Annual, monthly and seasonal distribution of cut-off lows during the statistical period In the statistical period of 33 years (1986-2018), a total of 632 cut-off lows with a lifespan of 2 days and more were identified. The average was 18.87 days for each year. The trend line or regression during the statistical period shows that the amount of cut-off lows is increasing. The share of cut-off lows in heavy rainfall in the four regions of Iran In the northwestern region of Iran, the highest percentage of the effect of shear compressions on heavy rainfall is in Kashan, Takab, Mahabad, Maragheh, and Tabriz stations, respectively. The lowest percentage of the impact of this phenomenon on heavy rainfall was in Khorramabad, Karaj, Babolsar, and Parsabad stations, respectively. In the southeast region, the highest percentage in Chabahar, Bandar Abbas, and Sirjan stations and the lowest percentage were in Jask, Zabol, and Khash stations. In the southwestern region, the highest effect is in Bushehr and Kish stations and the least effect is in Omidieh and Masjed Soleiman stations. In the Northeast, the highest share was in Birjand, Ferdows, and Tabas stations and the lowest impact was in Gorgan, Mashhad, Quchan, and Bojnourd stations. The amount of heavy rainfall and the effect of cut-off lows in it in different regions and Iran The highest occurrence of heavy rainfall due to cut-off lows was in the northwest region with (36.62 occurrences) and the lowest in the southeast region with (8.5 occurrences). In research study stations (76 stations), the frequency of heavy rainfall during the study period was average (124.76 events) and the effect of shear cut-off lows on heavy rainfall in total (26.1 events) in the station has been.   Conclusion A total of 632 cut-off lows with a lifespan of 2 days or more were identified in the research area. The trend line of the statistical period has a slight positive and increasing slope; the most occurrences of cut-off lows is in October, March, and January. The lowest incidence of cut-off lows is in July, August, and June. Seasonally, the highest number of cut-off low events was in spring, winter, and autumn. The highest occurrence of heavy rainfall under the influence cut-off lows was in the northwest region and the lowest in the southeast region during the study period. Therefore, it can be concluded that the entry of cut-off lows from the northwest and the proximity of the northwest region to the formation location of cut-off lows may be a factor contributing to the highest frequency of heavy precipitation events influenced by cut-off lows. Furthermore, the distance of the southeast region from cut-off lows indicates a lesser impact of this phenomenon on heavy precipitation in this area.