Desert
Volume:16 Issue: 2, Summer - Autumn 2011

Drought is a normal, recurring feature of climate phenomena; it may occur virtually in all climatic regions. The effects of drought accumulate slowly and its impacts are spread over a larger geographical area than other natural hazards. Drought is a natural hazard originating from a deficiency of precipitation that result in a water shortage for some activities or some groups and is often associated with other climatic factors such as high temperatures, high winds and low relative humidity that can aggravate the severity of the event. Iran is frequently affected by recurring droughts. In this research the Qom province with an area 11500 km2 that located in an arid and semi arid region of Iran was selected. Eighth site of rangeland were chosen that represented rangeland situation in the study area. In these sites relative factors such as plant cover, density, yield, regeneration, land cover were measured in 60 plots with 2 m2 area along the 4 transect with 400 m along. Rangeland yield was measured with the cutting and weighting method in a quarter of plots, and the total yield in each site was obtained from the regression models between plant cover and species yield. Data series were cumulated for 9 years (1998-2006). Palmer drought severity index (PDSI) carried out in this study. The objective of this study is to performance of the PDSI to assessment of drought in the rangeland of the Qom. The analysis of results indicated that each site growth season is different from another. The rangeland yield is not related to the annual rainfall, but the best relationship was between rainfall in growth season and range yield. Also the study showed that the highest frequency of significant models is related to March-July period.

The main objective in the present study was to assess the spatial variation of chemical and physical soil properties and then use this information to select an appropriate area to install a pasture rehabilitation experiment in the Zereshkin region, Iran. A regular 250 m grid was used for collecting a total of 150 soil samples (from 985 georeferenced soil pits) at 0 to 30, and 30 to 60 cm layers. Soil samples were analyzed for pH, EC, N, K, P, Na, Ca, Mg and SAR. Conventional statistical methods and geostatistics were performed in order to analyze soil properties spatial dependence. Mean, standard deviation, skewness, and kurtosis for all measured variables were evaluated. All variograms generally were well structured with a relatively large nugget effect. Soil properties such as pH, P semivariograms were best fitted by spherical models, while SAR, Na were best fitted by spherical models. In the beginning kriging were performed in order to analyze spatial variation of chemical and physical soil properties, then for enhancing estimation accuracy and comparing results we used cokriging technique. Comparison of the results using statistical techniques showed that kriging technique has acceptable accuracy in characterizing the spatial variability. Also results showed that although kriging technique has acceptable accuracy in characterizing the spatial variability of soil properties but if higher accuracy is needed, cokriging is preferred to kriging particularly when the extra variable has been used.

Evaluation of Sediment yield in watershed scale is considered so important for implementation of soil conservation, watershed management, environment, dam construction and water resource management. Using empirical model is one of the approaches of evaluating Sediment yield. This research in Kasilian watershed evaluates Sediment yield by using Geomorphology method and EPM model with Arc View GIS soft ware. In Geomorphology method four effective factors including slope, lithology, erosion faces and land use were used and information layers were made by combining (over lay) them, then homogen unites were produced. Finally sediment yield were evaluated in each one of them. EPM model which was used in Yugoslavia for the first time used four factors including slope, lithology, landuse and erosion condition in each one of hydrological units and by using annual mean of precipitation and temperature, also sediment ratio, evaluates sediment yield. After evaluation and comparison it was found that the amount of sediment yield in Geomorphology method was 3.6% less (1197 ton/year) and EPM model was 4.8 times more (5322 ton/year) than field observation, (1243 ton/year).

During an 11 days mission in February 2000 the Shuttle Radar Topography Mission (SRTM) collected data over 80% of the Earth''s land surface, for all areas between 60 degrees N and 56 degrees S latitude. Since SRTM data became available, many studies utilized them for application in topography and morphometric landscape analysis. Exploiting SRTM data for recognition and extraction of topographic features is a challenging task and could provide useful information for landscape studies at different scales. In this study the 3 arc second SRTM digital elevation model was projected on a UTM grid with 90 meter spacing for a mountainous terrain at the Polish - Ukrainian border. Terrain parameters (morphometric parameters) such as slope, maximum curvature, minimum curvature and cross-sectional curvature are derived by fitting a bivariate quadratic surface with a window size of 5×5 corresponding to 450 meters on the ground. These morphometric parameters are strongly related to topographic features and geomorphological processes. Such data allow us to enumerate topographic features in a way meaningful for landscape analysis. Kohonen Self Organizing Map (SOM) as an unsupervised neural network algorithm is used for classification of these morphometric parameters into 10 classes representing landforms elements such as ridge, channel, crest line, planar and valley bottom. These classes were analyzed and interpreted based on spectral signature, feature space, and 3D presentations of the area. Texture contents were enhanced by separating the 10 classes into individual maps and applying occurrence filters with 9×9 window to each map. This procedure resulted in 10 new inputs to the SOM. Again SOM was trained and a map with four dominant landforms, mountains with steep slopes, plane areas with gentle slopes, dissected ridges and lower valleys with moderate to very steep slopes and main valleys with gentle to moderate slopes was produced. Both landform maps were evaluated by superimposing contour lines. Results showed that Self Organizing Map is a very promising and efficient tool for land form identification. There is a very good agreement between identified landforms and contour lines. This new procedure is encouraging and offers new possibilities in the study of both type of terrain features, general landforms and landform elements.

Different types of sediment trap have been introduced so far to be used in erosion measuring stations, each with its own advantages and disadvantages in trapping aeolian particles. These traps have different collection and retention efficiency due to aerodynamic conditions. Some characteristics such as isokinetic feature of the trap, collection efficiency, time needed to download sediment, capability of installation in different altitudes and capability to collect sediment from different geographical directions are the criteria used to assess the efficiency of different types of sediment traps. In the present study Isatis Suspension Trap (Isatis SUSTRA) was tested in a wind tunnel and wind erosion measuring station. This is a kind of passive trap and its sediment collecting efficiency varies between 55% to 88% for 5 to 9 m/s velocities respectively in the height of 15cm. Although the efficiency of the trap in low wind velocities is less than 55%, it is remarkable comparing with other traps. Larger mouth of the trap provides it with vaster opportunity to trap sediment. Isatis SUSTRA has the capability to segregate sediments in different geographical directions. This privilege leads to 1) possibility to analyze horizontal distribution in different geographical directions, 2) determining the most sediment producing fraction and easy recognition of the source, 3) estimating moved materials such as dissolved salts or heavy elements in mine range) through separating sediment samples and 4) easy installation in different altitudes and enough capacity to reserve aeolian sediment. Generally speaking, the results from indoor and outdoor tests indicate that Isatis SUSTRA has appropriate capabilities with regard to collecting efficiency, keeping, sediment reserve capacity and easy download in hard conditions.

Wind erosion is a major environmental issue affecting land resources and socio-economic settings in Iran. This paper outlines a study undertaken to provide a new tool to manage wind erosion from physical and economic perspectives. The southern part of the Varamin Plain in south of Tehran is used as a case study. The focus of this study is on exploring the economic and physical impacts of 16 vegetation-based scenarios for wind erosion management as well as conducting a trade-off analysis using the Multi-Criteria Decision Making (MCDM) technique. This involves developing a modeling system to assist decision makers in formulating scenarios, analyzing the impacts of these scenarios on wind erosion, and interpreting and suggesting appropriate scenarios for implementation in the area. The Iran Research Institute of Forests and Rangelands (IRIFR.1) model has been selected to create the wind erosion hazard maps for the present condition and for the possible vegetative management scenarios. The Spearman’s correlation coefficient indicated a high conformity between the hazard classes of wind erosion map predicted by the IRIFER.1 model and ground evidences. Using the Delphi method weights of wind erosion, gross margin, and establishment costs indices have been determined 0.5, 0.3, and 0.2, respectively. This indicates the high importance of wind erosion issue from experts’ consideration. Standardization and trade-off analysis of indices showed that a scenario with a combination of all possible management actions ranked as the best scenario (highest score) despite incurring the largest establishment costs. On the other hand scenarios with single management actions resulted in lowest scores. Finally, the sensitivity analysis of the chosen modeling approach in this study indicated the robustness of the results.

The geographical distribution of growing degree-days (GDDs) within Iran was studied using GIS-based maps. GDDs were calculated using daily thermal parameters (daily maximum and minimum air temperature). Based on the purpose of the study and climatic conditions of Iran, the average value of 5◦C was chosen for GDD calculation. The calculations were carried out using daily weather data of 113 meteorological stations throughout Iran. The clustering of the 113 point stations’ data were achieved by using statistical models combined with a digital terrain model. The final outcomes were five GDD maps (two for start and end of heating period, one for January, one for cold season and the last one annual growing degree days). The relationships between calculated GDDs and key variables that may affect temperature were carefully studied. (e.g. geographical data of latitude and longitude, elevation, nearest grid distance from the sea) Geographical distributions of GDDs were found to be correlated closely with the climatic types of different regions that are mainly based on relief. The distribution of the GDDs presented in the maps showed that the calculated values were close to the measured ones, which confirmed the validity of the GIS-based approach. In few cases significant differences between predicted and calculated values were observed, mostly in the regions with less number of weather stations. Consequently, the highly accurate generated maps can be used as a useful tool for prediction of crops and pests phonological events and crop modeling.

In order to evaluate the yield, yield components and protein contents of two wheat cultivars (Zarrin and Gaspard) in sole cropping and intercropping systems,an experiment was conducted using replacement serious technique and different combinations of intercropping with high plant density and optimal of each cultivar. A factorial experiment was conducted in the form of randomized complete block design (RCBD) with three replications at the research farm of Agriculture Faculty of University of Zanjan at 2008-2009. The results showed that planting patterns has significant effect (α= 0.01) on grain yield, the average number of grain per spike and protein content of each cultivar.The effect of plant density levels on grain yield of Zarrin cultivar was significant (α= 0.01).The results indicated that the highest grain yield(9611 kg ha-1) was obtained from 2:2 ratios of (50% Zarrin+50% Gaspard) cultivars in plant density of 400 seed per m2 which had Land Equivalent Ratio (LER) above 1.79.Land equivalent Ratio Index(LER) calculation showed that all intercrops had advantage compare to sole cropping system.

This research studies the potential impact of climate change on future trend and changes of two well known drought indicators namely RDI and SPI in Yazd meteorological station, in central part of Iran. For this purpose, data of HadCM3 model that were resulted from GCM-runs based on the IPCC-SRES scenarios of A2 and B2 were acquired and analyzed for projection of daily Tmin, Tmax and precipitation for the projected period of 2010 to 2039. RDI and SPI drought indicators then were calculated and validated based on corresponding observations of historical period (1961-1990). Comparison of the results indicate that SPI and RDI of A2 scenario would have a negative trend along with the projected years, while these indicators tend to have positive trend when resulted from B2 scenario. The latter result demonstrates an increase of vulnerabilities based on up coming droughts.

Crops growing in salt-affected soils may suffer from physiological drought stress, ion toxicity, and mineral deficiency. A pot study was conducted in 2004-2005 in the Aghala area (northern Iran) to study the effect of different salinity levels, i.e. ECe= 3 (control), 8, 12 and 16 dS m-1 on wheat grain, yield components and leaf ion uptake of four Iranian wheat genotypes, i.e. Kouhdasht, Atrak, Rasoul and Tajan. Treatments were replicated three times in a completely randomized design in a factorial arrangement. Desired salinity levels were obtained by mixing adequate NaCl before filling the pots. Soil water was maintained at 70% of available water holding capacity. Results revealed that Kouhdasht and Tajan showed highest and lowest grain yield and its components as compared to other cultivars at different salinity levels. Leaf Na+ and Cl- concentrations of all genotypes increased significantly with increasing soil salinity, with the highest concentrations in Tajan, followed by Rasoul, Atrak and Kouhdasht cultivars, respectively. Highest leaf K+ concentration and K+: Na+ ratio were observed in Kouhdasht cultivar, followed by Atrak, Rasoul and Tajan, respectively. Therefore, Kouhdasht and Atrak were identified as the most salt-tolerant genotypes as compared to two other wheat genotypes.

Charcoal rot diseases of melon caused by Macrophomina phaseolina is one of the most important diseases of melon occurring in regions with variable climate. Reduction of yield of melon by this disease has been reported up to 100% in some of Garmsar field. Salinity which can cause the important trouble in plant metabolism and nutrition is present in Semnan and Garmsar areas. Melon is susceptible to salinity stress, therefore salinity stress may increase the susceptibility of melon to M. phaseolina. Different levels of salinity including, 0, 10, 25, 50 and 75 Mmol NaCl/l with and without fungal pathogen on two current cultivars of melon (Ivaneki and Susski) were investigated at the field conditions in Semnan and Garmsar areas. A factorial analysis for completely randomized design was used in these experiments with three replications. At all experiments, significant differences were observed among the different levels of any factors investigated including, cultivars, salinity and fungal pathogen presence. Interactions between investigated factors were significant too. The factors investigated in these experiments, clearly suggested the occurrence of a wide effect of salinity stress on charcoal rot development on melon cultivars and showed the importance of salinity management for decrease of disease severity.