نشریه پژوهش های آبخیزداری
پیاپی 94 (بهار 1391)

Hydrological drought is the effect of precipitation scarcity on ground or surface water resources including river flow، reservoirs، lakes and ground water. On the other hand، one of the methods to deal with drought is its occurrence probability prediction. Therefore، this study focuses on probability prediction of wet and drought periods occurrence and its intensity in the Kashafrood watershed. For this reason، all existent stations were considered and monthly discharge data of 16 hydrometric stations with correct and suitable data in this region were used. In the next step، transition matrix of the region was designed using Markov Chain and probabilities of hydrologic drought occurrence of these stations considering their intensity was computed. Finally، all stations were compared and probability of an intense drought occurrence was calculated. The results of monthly discharge consideration showed that the probability of very dry، dry، semi-dry، medium، semi-humid، humid and very humid discharges in the study area were: 79. 05، 12. 47، 4. 54، 1. 78، 0. 85، 0. 63 and 0. 69 of percent respectively. On the other hand، drought occurrence probability in this region is very high and equal to 95. 5% and wet occurrence probability is 2. 28% and also with probability of 1. 78% in the study area there would be medium current discharge.

In order to recognize and mapping domains of the real deserts، it is needed to gather a tremendous data and information regarding environmental parameters such as Geology، Geomorphology، Climatology، Hydrology، Pedology and Vegetation cover. In fact these environmental parameters and their interaction effects lead to form and develop the real deserts. in this paper was tried to study specification of desert areas related to climatically and geomorphologic factors. In climatology، these factors are the amount of precipitation، coefficient of variation، irregularity coefficient and daily average intensity of precipitation، annual average temperature and amount of evaporation which were calculated for each station in every study province separately. In geomorphology، by using geological and topographic maps with scale; 1:250000 and ETM satellite images and combination of their data، the geomorphologic features for desert such as; pedimonts، badlands، salty dome and evaporate formation، salty flats، sand dune hills، reg and etc. Segregated for every study province as a digital map. After controlling maps in field and laboratory، we prepared a country map with distinct Coordinate System and Georeference and transferred province maps to country map. After digitizing final maps، the results showed that; the whole areas which known as climatology and geomorphology deserts are respectively (700991&287316 km2) of Iran map. each individual layers covers different desert area on the map. Thus، if climatic parameters are used to determine desert area only 42. 9% of Iran is accounted، while if the geomorphologic parameters are used، 17. 4% of Iran is known as a desert. Crossing and matching of two layers (common parts of overlaying) was 24. 7% of the geomorphoclimatological deserts of Iran.

Rangelands contain between 10 and 30% of global soil organic C reserves and may be an important terrestrial ecosystem for carbon sequestration، most of rangelands have been converted to agriculture use but less C tends to be stored in them. The purpose of this study was to compare content and distribution of soil carbon sequestration in native rangelands، rangelands that were cultivated and then 1) seeded with non-native perennial grasses (Agropyron elongatum and Agropyron desertorum)، (2) seeded with non-native shrub (Kochia prostrata)، or 3) cropped annually with wheat، In semiarid rangelands of North Khorasan Province، Iran. The sampling method of vegetation cover and soil was randomized systematic and was collected from 30 1m2 plots in the along with 3 transect (100m). The content of above ground and under ground biomass carbon، litter carbon and soil organic carbon (in two depths 0-15، 15-30 cm) was determined. The result showed that the total carbon sequestration in native rangelands and soils under K. prostrata، A. elongatum and A. desertorum and wheat-fallow systems was 38. 71، 23. 66، 14. 47، 18. 32 and 13. 57ton/ha، respectively. The highest and the least content of carbon sequestration were measured in plant communities، Native rangeland and Wheat-fallow، respectively. Carbon sequestration in soils under K. prostrata was been similar to native rangelands. The results of carbon distribution showed that the soil organic carbon content was >90% of total carbon sequestration. It was concluded that K. prostrata can sequestrate soil organic carbon much more than other treaements. soil is the most impotant sink for organic carbon storage in this rangelands.

This research compares the indices efficiency of Artemisia sieberi and Astragalus ammodendron distribution pattern in Markazi province. In the key area of each site 4 transects (100m) were established based on random- systematic sampling method. Vegetation sampling was performed along each of transects in 15 selected points. Distance indices included Johnson and Zimer، Eberhart، Pielou، Hopkines and Holgate were used in each point. The distance of understudy plants to nearest plant، distance among selected plant and its nearest neighbor، and distance between the point and the second plant was measured. Quadrate indices included Green، Lioyd، Morisita and Standardized Index of Morisita. In all 15 points، density parameter of selected species was estimated. Results showed A. sieberi distribution pattern has equally and، A. ammodendron has random with a tendency toward clumped pattern. The More was in equality of the species، the more in converging of distance and quadrate indices. However the accuracy of distance methods was more than quadrate methods. Generally، those vegetation types that distributed clumped pattern showed less efficient quadrate indices due to the problems of number، area and shape of quadrates. So، quadrate indices show higher tendency to random pattern.

In order to study the effect of deforestation and tillage practices on soil erodibility، a loess hillslope was selected in eastern Golestan province، Agh-Su watershed. Five pedons in forest land use and also five pedons in adjacent cultivated land were dug on each slope position and studied morphologically. Some undisturbed clods were also sampled from different soil horizons with Kubiena boxes for microscopic studies. Total fifty samples were taken from surface layers of forest and also cultivated land use for physico-chemical analysis. Results showed that the amount of silt particles increased from 57. 6% in surface layer of forest to 68. 4% in cultivated land use. The amount of silt and very fine sand particles also increased in cultivated area relative to forest. Organic matter decreased from 3. 5% in surface layer of forest to 1. 0% in the same layer in cultivated land. Deforestation and tillage practices reduced the MWD value from 1. 49 mm in forest to 0. 88 mm in cultivated land. Micromorphological studies revealed that favorable granular and crumb structures were converted to compact and massive by deforestation. Due to these changes، soil erodibility factor increased، especially in the shoulder، backslope and footslope positions.

Determination of grazing capacity in rangelands is an important factor for livestock husbandry. Improved forage quality is an important goal for improving animal performance. The aim of this study was to assess near infrared reflectance spectroscopy (NIR) as a rapid and reliable method for estimating quality parameters in nine range species as three grasses Bromus tomentellus، Agropyron intermedium and Dactylis glomerata، three forbs Achillea millefolium، Coronilla varia، Centaurea virgata and three shrubs Scariola orientalis، Artemisia aucheri and Thymus kotschyanus. NIR calibrations were derived for crude protein (CP)، dry matter digestibility (DMD) and acid detergent fiber (ADF). To maximize variability of samples for analysis، were collected at three phenological stages as initiated growth، full flowering and seed ripening in ranges of central Alborz (Taleghan). Samples were dried and grinded using standard laboratory methods. A sub samples were analyzed using standard laboratory chemical procedures to estimate CP، DMD، ADF and total ash. The other sub samples were scanned by means of a 20-filter set of the Inframatic8620. NIR spectra were recorded for each sample. A separate independent set was used for predictions. The calibrations obtained from this study had a high level of accuracy based on coefficient of determination (R2)، standard errors of calibration (SEC) and standard errors prediction (SEP). SEC were ranged from (0. 15 to 1. 09)، (0. 21 to 0. 86)، (0. 83 to 3. 94) and (0. 52 to 4. 96) and SEP were ranged from (0. 13 to 0. 75)، (0. 17 to 0. 61)، (0. 62 to 3. 34) and (0. 31 to 3. 84) for CP، Ash، DMD and ADF، respectively. The correlation values between laboratory data and NIR prediction was very high for all traits in particular for CP. The results confirm that NIR can use a rapid، precise and cost effective method for measurement quality traits in range species.

Estimation of vegetation features from space is a great challenge for agronomist، hydrologist and meteorologist communities. Now، the use of vegetation indices to estimate vegetation characteristics is very popular. They are empirical combinations between Visible (generally Red، R) and Near Infrared (NIR) reflectance that show good correlation with plant growth، vegetation cover، and biomass amount. The main objective of this study was to introduce a suitable model based on satellite images in order to estimate vegetation Fraction in Sade Nahrein basin (Tabas، Yazd، Iran). To do so، IRS-LISIII (2007)، ETM+ (2005) and vegetation fraction measured in fielwork (54 plots) have been used. Making comparable field data and pixel values، the average value of pixels located in the sampling sites was extracted and then 11 different vegetation indices were calculated. In the next step، the 6 output models have been evaluated using linear regression method and fitting the regression line between observations and estimated values in the validation data. The results showed that the model in which MSAVI1 was used has the highest accuracy (R2=0. 866) and therefore is the most suitable model for estimation of vegetation fraction in the study area.

In this paper effective environmental factors on plant distribution of Taleghan rangelands has been investigated Then، sampling in each unit was done along two 150 meter transects. 15 plots (1 m2)، established along each transect in 10 meter distances. The kind and the amount of existing species and the percentage of vegetation cover were determined in each plot. At the beginning and at the end of each transect، a profile was dug and soil. Sampling was done from 0-30 centimeter. Among soil properties، clay، silt، sand، organic material، lime، pH and EC were measured. To determine the major factors affecting plant distribution variations، Principle component analysis was used. The results showed that among studied factors aspect، texture، lime، parent material had the most influence on plant distribution.

One of the slopping processes which created much damage in many locations of Iran and the world is Landslide phenomenon. Making landslide susceptibility map provides the possibility to recognize susceptible areas and to verify them in the environmental programs. Purpose of this research is mapping susceptibility of landslide in Chardavel watershed in Ilam province by establishing informational layers and effective factors in occurrence of landslide via geographical information system (GIS) and fuzzy logic theory which involves operators fuzzy subscription، algebraic Sum، algebraic product and gamma fuzzy. The location of the landslides was determined by using regional photographs and satellite images and LSM. In this work، input information set in assessment of potential hazardous landslide includes nine factors: slope، aspect، elevation، precipitation، distance from road، distance from fault، distance from drainage، land use، and lithology. For comparing maps resulted from landslide susceptibility mapping by quadruple operators in fuzzy logic، density ratio (Dr) index is used. Based on this index، the map obtained by fuzzy gamma operator is more appropriate than other operators in separating suitably between casts of landslide risk. Thereby، more than 57 percent of landslides in this region occurred in 52. 7 percent of the lands and in two cast of high or very high danger. Finally، to estimate the amount of the precision and efficiency of fuzzy quadruplet operators، the evaluation generated maps compared with real zoning maps of basin. Results show that fuzzy gamma map has high overlay with real maps، the highest percent of the overlay of two maps in fifth class (Very High) is 43. 3 % and the lowest percent of overlay in third class (Moderate) is 12. 1 %.

The aim of this study was to characterise the spatial variability of soil saline and sodic properties in part of the western Karoon lands in Khozestan province. A total of 120 samples from the 0-30 cm of soil depth in a semi-systematic grid (200*200 m) were collected in order to provide the needed data. pH، pasted soil electrical conductivity (ECe)، particle size distribution، sodium absorption ratio (SAR) and soluble Ca and Mg were measured in these samples. Spatial variability of parameters was investigated using semivariance and the ratio of nugget variance to total variance. Krigin method was used to create map of the needed data. The validation of the maps was evaluated using mean error (ME) and root mean square error (RMSE) between the observed and the estimated values. Results showed that the experimental variogram of chemical properties was fitted with a exponential and spherical model and 4 to 4. 5 km radius was determined for spatial range in these saline and sodic parameters. All of the parameters were moderately to strongly spatially corolated. Spatiall variability of soil chemical properties is a fundamental element of site-specific crop management. The objective dependent based on these results، spatial patterns of chemical properties are linked to parent materials and soil types. Variance maps of these parameters show that ECe، SAR particle size distribution and PH is largely increased by sampling region in neighboring line and also in lower sample density of region.