نشریه هواشناسی کشاورزی
سال هشتم شماره 2 (پاییز و زمستان 1399)

The plan to merge the National Meteorological Organization into the Ministry of Energy is currently under investigation by the specialized commission of the Islamic Consultative Assembly (Parliament).  The reasoning for the proposal could be due to the very close affinity of technical issues, areas of work on meteorological and hydrological topics, the high information dependence of these two sectors, the parallel works and finally waste of the country's capital. In the present note the tasks overlap of the National Meteorological Organization with those of the Ministry of Energy considers small, and limits just to the measurements of some water balance parameters estimation. As such, it has been argued that creating a Common Database could provide the same result as if merging the two organizations. Therefore, it is suggested that the following two options be considered: 1) either the current status quo be maintained, or 2) upgrade the current organization to a higher level under the presidency. Finally, in both cases, to play a synergistic role in providing qualified data and data processing, the emphasis is on creating a Common Hydrometeorological Database.

Considering the significant effect of chilling and frost phenomenon on agricultural production in Iran, the aim of this study is projection of minimum temperature in three provinces of Kurdistan, Kermanshah and Ilam, Western of Iran. For this purpose, the data of 17 meteorological stations during the baseline period of (1989-2018) were collected. Then, the HadGEM2 and CanESM2 climate models outputs were statistically downscaled using LARS-WG and SDSM weather generators under three climate change scenarios of RCP2.6, RCP4.5 and RCP8.5 during future period (2021–2050) and compared with observed data. The performance of the two weather generators, were compared using MSE, RMSE, MAE and R2 indices. The results indicated the good accuracy of both statistical models in simulating the minimum temperature in the study area; however the SDSM model performed better than the LARS-WG. The projected changes of minimum temperature compared to the baseline period revealed a significant increase varying between 0.6 – 1.5 oC in study stations. The most significant change was observed in northern parts of study region especially in the Saqhez and Zarineh stations. The findings of this study can be used in frost risk management and agroclimatic planning in the region.

Potential yield of a specific crop cultivar is obtained when it is grown with water and nutrients non-limiting and biotic stress (pest and diseases) effectively controlled. In 2019, a study was conducted to estimate the potential Total Dry Matter (TDM) of forage maize and tomato under optimum growth conditions, using FAO growth model under climatic condition of Abhar region, Iran. The results showed that the potential yield of TDM and the grain in hybrid cultivars of maize which are tolerant to high plant density with leaf area index of 3.5, harvest index of 52% and growing season of 125 days, will be about 28.67 and 14.91 t.ha-1, respectively. The potential yield of tomato with leaf area index of 2.8, harvest index of 65% and growing season length of 148 days will be 212 t.ha-1.Considering the perennial nature of the latter; its yield might be increased by prolonging the harvesting period. According to the length of growth season of maize and tomato crops, the irrigation water requirement was estimated 703.9 and 830.1 mm, respectively. Findings of the study may be applied in improving the yield of study crops using revised management options under climatic conditions of the region.

Each plant requires specific amount of heat units complete its growing season. In this study, the heat units of different phenological stages of three cultivars of black raspberry have been investigated. After maintaining the chilling requirement, the studied cultivars were transferred to the greenhouse. The cultivars; Silvan (early), Marion (medium) and Topai (late) spent 91, 109 and 118 days from planting to harvest in the greenhouse, respectively. The results showed that the heat requirements of different raspberry cultivars to complete the phonological stages are different from each other. Early black raspberries variety has a lower heat requirement of 43,000 Cumulative Degree Growth Hours (CGDH) and produce larger fruits than their parent medium maturing variety with a heat requirement 51,000 CGDH. Under the climatic conditions of Sari, early maturing cultivars showed the capability to produce fruit in a 91 days period, while the same variety cultivated in the greenhouse, produced the fruits 2 month earlier, which is important in off-season production. For the Topai cultivar, which differs from early and middle cultivars in most traits, the phenological stages were longer and the single fruit weight and stalk length were higher comparing to other cultivars. However, in this cultivar, the buds break occurred earlier than other cultivars, although the higher heat requirement from fruit formation to ripening i.e. 55000 CGDH led to later ripening of the crop. Further studies on bioclimatic requirement of other blackberry varieties for proper management decisions and improving the production is recommended.

Global warming is leading to gradual and tremendous climate change following the increase in greenhouse gases. Methane gas can be produced in anaerobic processes in soil, such as paddy fields. Therefore, in the agricultural sector, waterlogged rice cultivation is one of the main sources of this methane gas emissions. On the other hand, straw burning brings a huge amount of pollutants to the atmospher. In this regard, a study with four experimental treatments was conducted: (a) without straw (control), (b) rice straws incorporated into the soil,  (c) burned rice straws left in the field, and finally (d) burned air-dried rice straws left from first cropping harvest. The experiment was carried out on the experimental field of Sari Agricultural Sciences and Natural Resources University. Methane gas sampling was performed at 10- day intervals and carbon dioxide gas sampling was performed one day after straw burning and then in three stages in the second cropping season. Finally, in order to compare the treatments in terms of methane and carbon dioxide emissions, the carbon dioxide equivalent of methane gas was calculated.The findings showed that the highest methane emission was from rice straws incorporated into the soil (6.75 mg/m2.day) and the lowest emissions were from the control treatment (2.97 mg/m2.day) ) and burned rice straws air-dried after harvest (2.62 mg/m2.day). Also, the results of carbon dioxide emissions during the second cropping season showed that the highest amount was from burned rice straws left in the field treatments (133.93 mg/m2.day) and the lowest amount was observed from burned rice straws air-dried after harvest (67.08 mg/m2.day). Finally the results of the total greenhouse gas emissions measured in the whole period showed that wet and dry straws burned treatments could have the potential to increase global warming almost 8 times more than the control treatment.

The heavy rainfall event of April 2019 with 230 mm, i.e. 46% of the mean of annual rainfall of southwest Iran, over 4 days caused the overflow of Dez and Karkheh large dams and huge financial losses. In order to determine the characteristics of stable isotopes of 2H and 18O of this extreme event, 43 samples of rain water were collected in the area about 41000 (Km2) in southwestern Iran with altitude ranging between zero to 2814 m above sea level (a.s.l). The variations of the isotopic values of δ18O and δ2H were 4.71 to -4.76 and -26.06 to 29.2, respectively. The local meteoric water lines were calculated during the flood event and compared with the corresponding global, Mediterranean and other parts of Iran values as well as neighboring countries. According to the equation of LMWL (δ2H = 6.5996 δ18O + 7.561) and deuterium excess (between -9.26 to 15.55 with average value of 7.85), it is concluded that the source of precipitation in the study period was the integrated effect of the of Mediterranean and Red Sea air masses. Deuterium excess increased from the south and southwest of the study area to higher altitudes (located in north and northeast), indicating depletion of the isotopic composition toward the high altitudes.

MODIS-based Gross Primary Production (MODIS-GPP) as a proxy of the potential of vegetation cover in the atmospheric carbon sequestration was evaluated using Flux Tower measurements (Flux Tower-GPP) across three sites, broadleaved temperate deciduous woodlands, in the south of England. Ensuing to the normal evaluation of data distribution, the mean value of MODIS-GPP (cell size: 1km2) compared with the Flux Tower-GPP through the Two-Tailed T-Test (P < 0.05). A significant difference between two groups, MODIS-GPP vs. Flux Tower-GPP, was found that there is a measurable difference between the groups and that, statistically. The results show that Flux Tower-GPP values for both Alice Holt and Wytham Woods sites are higher than the MODIS-GPP, while in Pang Lambourne the opposite is true due to land cover heterogeneity. The trend of seasonal changes of both groups is the same and the increase of GPP in plant phenology is observable in all sites. GPP values gradually increase to early of May, then a prompt rising observed in May that extend to late of summer which arisen from development of solar radiation, day length and photosynthetic activity. In late of summer, GPP values gradually decrease so that by advent of autumn a rapid decline come about in the early of October that corresponds with senescence and abscission, due to decreasing temperature, which reflects the seasonal variation in terms of carbon uptake. The research finding reveals that the MODIS-GPP alone is unable to estimate accurately the potential of vegetation cover in the atmospheric carbon sequestration due to sub-pixel variability in plant functional type. On the other hand, despite at certain sites the meteorological bias influences estimates of GPP significantly and flux towers provide an excellent means to estimate accurately GPP across their footprint, they are sparse worldwide, even at the regional scale. Thus, the Flux Tower GPP may not truly be used to estimate a continuous GPP map at a larger area. Therefore, Flux Tower and MODIS individually have large uncertainty but their combination as a complementary could result in a robust estimation of GPP.