Irrigation
M. Mohammadi; M. Akbary
Abstract
Introduction: Sistan and Baluchestan Province, in southeast of Iran, is covering about 11 percent of the whole space of the country but is one of the driest provinces in Iran and its average annual rainfall is about 110 mm. The purpose of this study was to identify large-scale atmospheric circulation ...
Read More
Introduction: Sistan and Baluchestan Province, in southeast of Iran, is covering about 11 percent of the whole space of the country but is one of the driest provinces in Iran and its average annual rainfall is about 110 mm. The purpose of this study was to identify large-scale atmospheric circulation patterns causing extreme and widespread rainfalls during the warm seasons (spring and summer) in southeast of Iran (Sistan and Baluchestan province).Data and Methodology: Precipitation data of 6 synoptic stations of Sistan and Baluchestan province during a 30-year statistical period (1979-1998) were obtained from Meteorological Organization of Iran (IRIMO). The intensity of precipitation based on 90th percentile threshold and widespread precipitation index of at least ≥50% of the studied area were calculated. To identify the synoptic patterns of the upper atmosphere, the ERA5 data of the ECMWF European Center of Med-Latitude Weather Forecast with spatial resolution of 0.25° × 0.25° were obtained. The collected atmospheric parameters included mean sea level pressure (mslp), geopotential height (z), specific humidity (q), zonal (U) and meridional (V) wind components, relative vorticity (rv) and omega (w) and maps of the upper atmosphere were drawn at different levels using Gards software in the domain of 10 to 70E and 10 to 90N. Regarding the two selected characteristics, three events of heavy and widespread precipitation were determined.Results and Discussion: By analyzing the daily rainfall data over a period of 30 years (2018-1988) during the warm months of the year, the number of days with torrential and widespread rainfall in Sistan and Baluchestan province were determined. According to the index the previously defined floods and mudslides were obtained for 3 days with torrential and widespread floods that often occur in the spring, which are categorized to three main patterns including: 1- Gono Tropical Storm 2- Omega Blocking and 3 – 500 hpa trough system. The results showed that during the maximum 24-hour precipitation, in the first synoptic pattern, the southern cities of the province received the maximum precipitation due to the proximity of the storm’s core, but gradually from southern to northern latitudes, the rainfall declined considerably so that Chahbahar station had the maximum rainfall and Zabol station recorded zero rainfall. The storm is expected to move eastward as it moves to higher latitudes, but the high pressure formed on the Indian subcontinent acted as a barrier and directed the storm to the west, thus affecting the southern regions of Iran. In the second and third pattern, the location of Sistan and Baluchestan province in front of the trough axis and advection of cold weather of the northern latitudes were the main causes of instability that lead to heavy rainfall. The moisture of these rainfalls was obtained from Oman, Arabian Sea and Indian Ocean respectively. In the second pattern, the anticyclonic clockwise motions of the Arabian Sea has provided the moisture for extreme precipitation events. Common points of all three precipitation patterns are atmospheric moisture reduction in all three levels of the earth, 850 and 700 hectopascals from south to north of the province. This is mainly due to the distance from moisture sources as well as the arrangement and height of the roughness of Sistan and Baluchestan province, which has caused moisture trapping and prevented the transfer of sufficient moisture for the occurrence of torrential rains. In the second model, the amount of moisture reduction from south to north is less, which indicates the activity of the Arabian Sea high pressure and the power of this high pressure in moisture transfer. In general, with increasing altitude towards the northern regions, mainly rainfall systems have lost their moisture and unevenness has prevented the proper distribution of moisture in the province.Conclusion: In southeastern Iran, the spatial distribution of precipitation is strongly influenced by the proximity to the sea and the location of the topographic features. Upper air levels turbulences are the most common cause of air mass rise. The main factor in reducing heavy rainfalls in northern areas of Sistan and Baluchestan is the lack of sufficient water vapor to reach these areas. Extreme rainfall is more likely to occur in spring than in summer due to the appropriate thermal gradient in southeastern Iran. Finally, the results of the study showed that the possibility of precipitation in spring compared to summer due to the appropriate temperature gradient in southeastern Iran and the activity of Siberian and Northern European high pressure, the conditions for fronting in these areas are provided. Since the humidity of the southern oceans through atmospheric rivers has been effective in the occurrence of heavy rainfall in southeastern Iran, rising temperatures in the southern oceans due to global warming can strengthen moisture flows in the future and from this route to affect the intensity of rainfall in southeastern Iran.
saman fashkhorani; mohammad salighe; mehry akbari
Abstract
Introduction: The effect of climate factors plays an important role on agricultural products. In this case, there is not enough knowledge about the role of climatic elements in agricultural planning, therefore, there wouldnot be much achievements because it is proved that in most cases, the low yield ...
Read More
Introduction: The effect of climate factors plays an important role on agricultural products. In this case, there is not enough knowledge about the role of climatic elements in agricultural planning, therefore, there wouldnot be much achievements because it is proved that in most cases, the low yield of agricultural products is the result of not keeping and being unable to create a balanced climate. Temperature stresses are one of the most important factors in plant growth. In most plants, when the plant is exposed to extreme temperatures, physiological changes may prevent optimal plant growth. Therefore, plants need a specific temperature range for optimum growth and stepping outside of range is considered as a stress. Strawberries are generally herbaceous plants that are one of the most sedentary, dense, isolated petals without stems, more or less articulate with lower leaves and narrow stolon that are sensitive to temperature stresses. This temperature fluctuation causes major annual damage. Therefore, this study was carried out to investigate the extreme temperatures in the strawberry growing area in Kurdistan province (Sanandaj-Marivan-Kamyaran) and the effect of these stressful temperatures on strawberry yield, as well as future temperature prediction and future effects were investigated.
Methods and Approaches: In this study, the average daily temperature, maximum daily temperature and minimum daily temperature duringthe years 1381-1395 were obtained from Iran Meteorological Organization and the occurrence date of the last temperature (spring minimum temperature) for strawberry (5 ° C), which is actually the date of the beginning of the strawberry growth period. Also, the date of occurrence of the first stress temperature (maximum summer temperature) for strawberry (35 ° C) and the length of growth period of strawberry were estimated in the studied years. Data from the production and yield of strawberries were collected from the Jihad Agriculture Organization in Kurdistan province during this 15-year period. In order to study the effect of extreme temperature and the occurrence date of this temperature on the yield of strawberry, using Spearman correlation coefficient (SPSS), correlation between severe temperature and strawberry yield was calculated. Finally, in order to investigate the effect of climate change on the maximum and minimum temperature data in the future, using the SDSM model under the rcp26 scenario, CMIP5 climate scenarios were produced in the 2050-2020 and 2099-2099 periods.
Results and Discussion: The results indicated that the date of the extreme temperature did not change much and the latter extreme temperatures have tended to be more prevalent in the spring. The onset of the first extreme temperatures is also early in the summer of late July and we see an almost short (four-month) growth season for the growth of outdoor strawberries. Minimum temperature has the greatest effect on the yield of strawberries in April and the maximum temperature has the greatest impact in July. This issue is justified by the unfavorable temperature for growing strawberries and low yields in these months. The highest correlation between monthly average temperature and monthly yield of strawberries is in May and June. The simulated future data shows that in the months of the growing season (spring and summer), the temperature increases one to two degrees and the early minimum temperature and the maximum summer temperature will be lower than the base period.
Conclusion: The results of the correlation calculation between the date of the last event and the first critical temperature indicate a weak correlation, and it can be concluded that the occurrence of the first and the last extreme temperatures does not affect each other. The results of the study of the effect of the monthly average temperature on the monthly yield of strawberries in May and June showed that the average daily temperature of 12 to 25 °C, especially 17 to 20 °C, is higher on strawberries. Temperature higher and lower than this range (12 to 25 °C) reduces or stops growth. According to the data produced, the final temperature (minimum spring temperature) occurs a little earlier, and strawberries begin to grow in early March, but this could be risky and a sudden cold time causes a lot of damage. The maximum summer temperatures are also higher. This is true especially in June, when strawberries have the highest yield, it is not good and it stops plant growth. The strawberry growth season is expected to begin in March and end in June. Therefore, measures should be taken to prevent possible damage by raising awareness of the subject.
