نشریه هواشناسی کشاورزی
سال یکم شماره 2 (پاییز و زمستان 1392)

Leaf area index (LAI) and extinction coefficient (K) of wheat are the important parameters for estimation of intercepted solar radiation (RsL). Wheat daily intercepted solar radiation has been measured in many researches, but they are not suitable for using on shorter time increments. The beam angle of solar radiance differed on different hour in day and it must be considered for estimation of hourly RsL (SH) for crop growth models. For estimation of hourly RsL of wheat, an experiment was conducted in fields of Agricultural College at Shiraz University in winter 2009 and spring 2010. The values of hourly RsL, was measured using the difference between the values of measured solar radiation at upper and under the canopy. The results showed that the crop LAI increased after planting and reached maximum (4.89) on 174 days after planting and remained constant for 21 days. The values of wheat intercepted solar radiation was predicted using a method presented by other investigators and the minimum and maximum values of SH were estimated 0.064 and 0.41 when the values of LAI were 1.8 and 4.89, respectively.

The aim of this research was the evaluation of COUP Model for simulation of soil frost depth at Bijar synoptic station. The simulations were first carried out based on the default parameter values. Afterwards, 30 parameters that had a close relationship with soil frost depth were selected and calibration of the model was performed with adopting Generalized Likelihood Uncertainty Estimation (GLUE) method and simulations of the model for before and after calibration cases were compared. The periods of 1992-2006 and 2007-2009 were selected for model calibration and validation, respectively. On the basis of comparisons between model simulations and observations for soil temperatures at 20 and 50 cm depths and soil frost depth for before and after calibration, the results showed dramatically better performance after calibration compared with before that. The results of model validation showed a good correspondence between simulations and observations at more cases and the model simulations were able to follow observation fluctuations. However, some differences were available between simulations and observations. Some parts of differences are attributed to non-contribution of soil moisture data at calibration procedure and the other parts were attributed to uncertainties in model structure and its governing equations.

Urbanization has led to significant changes in the urban environment than natural conditions that urban microclimates are result of these changes. The purpose of this study is microclimate zoning of Isfahan city based on land cover types and investigating the effect of land cover types on urban microclimates. Isfahan city was divided into cells with dimensions 250×250 m. Different layers were defined in ArcGIS 9.3 software. The area percentage of each layer was determined in each cell. After weighting each layer, air temperature and relative humidity data of the 5 meteorological weather stations installed in Isfahan city were used to verify the layers weights. Microclimate zoning of Isfahan city was performed with weights given to each layer. The results showed that land use and land cover type have a significant effect on urban microclimate. Microclimate zoning is efficient for detection of cells with different temperature and humidity conditions. Microclimate code was lower in downtown where the density of residential areas and city streets are high in comparison with the suburbs where the density of agricultural lands and gardens are high. The evaluation results indicated that the method used in microclimatic zoning of the city was accurate and microclimate map is able to distinguish air temperature and relative humidity in the city.

AbstractAssessment of meteorological variables time series can indicate the effect of climatic factors on water resources and hydrological conditions. In this case, statistical methods are useful and effective tool to be considered. But to evaluate and quantify level of this impact, it is necessary to remove trends in the series and detrended series be used. In this paper, two detrending methods based on slope of line and Fourier series were used for deterending the annual temperature and precipitation time series in Ajichai basin. Performance of this methods was evaluated based on compare average long-term precipitation and temperature before and after detrending. Results of trend analysis for precipitation did not show the same general behavior, but the general trend of temperatures in the basin was rising. Detrending results also indicate the improper performance of both methods. In the first method differences in the data before and after detrending was high however, in the second method no difference was seen. To solve this problem, in this study a mixed approach was proposed to modify the first method. This method detrends time series based on the Theil–sen’s slope line exactly in the years after starting the trend that shows more reasonable results compared to the other methods. In this method, average of long-term precipitation and temperature in the basin changed from 328 to 339 mm and 11 to 10. 6 oC, respectively.

The aim of the present research is to generate the daily regional map of reference crop evapotranspiration (ETo) using minimum meteorological parameters for Grand Karkheh basin. To conduct this study, meteorological data from 24 synoptic stations located in Karkhe basin and surrounding sites were applied and the daily ETo for each site were calculated by Hargraves-Samani and FAO-56 methods in RefET Software. Furthermore, different interpolation methods were fitted on the results of both mentioned models. The best interpolation method was selected according to coefficient of the determination and Root Mean Square Error criteria. Results indicate that Ordinary Kriging is more accurate and reliable than other interpolation approaches for months of growth season (April-September) for generating the regional ETo maps in the study regions. The regional maps of ETo were derived and classified for months of growth season by ArcMap software using the selected interpolation method. Moreover, the area allocated to each classification obtained for each maps of ETo and in each month of the growth season both ETo methods in region scale were compared with each other. The discrepancies of ETo maps from two methods were more significant in the North and North-west of the study region. Regional map differences between two methods were found to be more significant in July and August.

Climate change affects precipitation and temperature patterns and hence, may alter the crop water requirements. This research was conducted to evaluate the effects of climate change on evapotranspiration of soybean in Gorgan province. LARS-WG model was used to generate temperature and rainfall data for future period (2013-2042) under emission scenarios of B1, A2 and A1B. The generated and observed weather data for baseline period of (1985-2012) were considered as inputs for a crop-weather model namely, SSM. Soil evaporation, crop transpiration and water requirement of irrigated and rainfed soybean crop were simulated for eight different dates of sowing ranging from the May 11th to 24th July with 10 days interval. Test of significance of means showed an increasing trend in daily maximum and minimum temperature for most of the months, and for mean monthly values of rainfall in fewer months. The outputs of SSM model showed that during future period, soil evaporation would slightly decrease, but plant transpiration would increase. This increase is more significant in case of rained crop for about 15 percent. Evapotranspiration showed not significant change for irrigated crop in future period, but in rainfed conditions a 10 percent increase has been revealed. Finally, rainfed cropping of soybean is not common in the region it can be concluded that climate change will not significantly affect water requirement of soybean in Gorgan region.

The growing trend of population and limitation of production resources, have led to make more attempts for increasing the crops yield. In present study the effects of temperature, precipitation and agricultural inputs (seed, fertilizer, pesticides and machineries) on cotton yield have been evaluated during the period of 2002-2011 in selected provinces of Iran. Required weather data were collected from Iran Meteorological Organization. Data were checked for normality and used for estimations by fixed effect data panel method. The results showed temperature increase during the growing season have negative effect on cotton yield. Such that, the yield would decrease 38 percent per one degree temperature rise. Besides, it was found that the cotton production trend has been decreasing in study regions. Considering the increasing trend of temperature and limitation of water resources, proper measures should be adopted for further adaption.