Desert
Volume:18 Issue: 1, Winter - Spring 2013

Land degradation, or desertification, is specific to arid, semi-arid, and dry sub-humid regions. The rate of this phenomenon is high in developing countries such as Iran. This research investigated desertification and mapping of desertification in Abuzaydabad, near Kashan, Iran, with an emphasis on land criteria using an IMDPA model. Different studies have assessed land degradation or desertification and resulted in the production of different regional models. The application of such models to another region requires reinvestigation of the criteria and adjustments for local conditions. The present study used the newest and best model for assessment. Three key regional criteria were defined for desertification: geology-geomorphology, soil, and wind erosion. A working unit map was made using a geomorphologic method and land use in each working unit was determined. Thematic databases were integrated and enhanced using GIS and its spatial modeling function. Using the developed land degradation or desertification mapping, it was found that of the total study area (16161 ha), medium desertification was found in 4792 ha and high desertification was found in 11369 ha.

Sand and dust storms are natural events that occur widely around the world, mostly in dry and bare lands. Over the past decade a large part of Iran has been affected by this phenomenon, and Tehran has not been excluded from this event. Therefore, having knowledge of spatiotemporal frequency variations can aid us in future management and storm trajectory assessment. In this study the synoptic anemometric data of Tehran Mehrabad stations over the past 47 years were used. Annual and monthly wind and storm roses were drawn to determine the predominant wind direction. The primary results indicated that the prevailing wind direction is western, but in summer, it is southsoutheastern. According to the threshold wind velocity (6.5 ms-1) about 12% of recorded data wascategorized into the storm condition.. Results also indicated that western, northwestern, and southwestern winds have the three highest rates of sand drift potential (Dpt), respectively. The temporal variability of dust storms showed that between 1951 and 2005, the largest number of days characterized by dust and thunderstorms was observed in the spring and summer. The average number of dusty days in spring and summer was four d/m, and the fastest winds ranged from 40 to 49 m/s-1. An assessment of dusty days over the past five decades revealed that the average number of dusty days has significantly increased from 10 days to 80 days. It seems that cyclonic circulations in the Monsoon Trough together with regional winds in central Iran are responsible for the transmission of dust particles over central Iran. Results and data from this study can be helpful in determining and predicting the critical dust storm period and in forming management strategies in order to minimize aftermath impacts.

The purpose of this study was to evaluate the species-environment relationships in arid and semi-arid rangelands of Nodushan, Yazd. The plant species cover and the environmental variables were measured at 9 sites. Soil samples were taken for measurement of 12 attributes in 0-10 cm and 10-80 cm layers. Vegetation was classified using twoway indicator species analysis (TWINSPAN). Data was analyzed using the ordination method of canonical correspondence analysis (CCA). Results showed that soil texture, organic matter, gypsum, salinity, C/N ratio, and elevation greatly affected the distribution of vegetation. Anabasis aphylla reflected the high salinity and saturation moisture content of soils. Ephedra strobilacea reflected a high level of soil gypsum and a high C/N ratio. Artemisia aucheri was characterized by a gradient of increasing elevation, high organic matter, and available water. Determining the vegetation-environment relationships at these sites facilitates the improvement and reclamation of arid and semi-arid shrubland ecosystems.

Desertification is recognized as a serious environmental threat in Iran because of its climatic-geomorphologic conditions. Desertification and land degradation in arid, semi-arid, and dry sub-humid regions, is a global environmental problem. Accurate assessment of the status and trend of desertification is instrumental in developing global strategies to prevent and reverse this problem. The goal of the present study was to discover and introduce criteria and quantitative indices and test modeling to monitor and assess desertification in the ecosystems of Iran. Past research has shown that effective factors for desertification can be categorized into nine groups of criteria. For each criterion is typified by a group of indices. All indices have been adjusted to natural conditions in Iran and their qualification is based on expert knowledge and the range of natural occurrence. The Iranian model of desertification potential assessment (IMDPA) was used to evaluate desertification risk in the Farasman region in central Iran. The results show that, in spite of common techniques, the proposed method has the best accuracy and produces precise results. The data were integrated over a regional geographic setting using a GIS, which facilitated data display and the development and exploration of data relationships, including manipulation and simulation testing. Results show that about 77% of the area fell into the moderate category, 15% fell into the low category, and the rest (8%) fell into the high category for desertification risk. It was found that the overall severity of land degradation and desertification in the study area has increased during the last two decades with highly and moderately degraded land accounting for 77% of the total area in 2010. The incorporation of natural and anthropogenic factors into the analysis provided a realistic assessment of the risk of desertification.

A rain gauge network should serve general as well as specific purposes such as water supply, hydropower generation, flood forecasting, irrigation, and flood control. The level of accuracy a network can achieve depends on the number and locations of gauges in the network. In this study, a rain gauge network was designed for Hormozgan province in the south of Iran. Monthly rainfall totals from 124 rain gauge stations in the period from 2000 to 2009 were used. This province can be logically divided to four regions using the De Martonne aridity index. Kagan’s approach was used to relocate the rain gauge network to obtain the optimal design. In this statistical method, the correlations were classified based on distance. Exponential models were fitted to the average correlations against mean distances in all regions. The number of gauges and the distance between gauges were computed to satisfy user requirements. The results showed that Hajiabad had the minimum value for distance (12 km) and Bandar Lengeh had the maximum value for distance (588 km). Spatial variation of rainfall in Hajiabad was greater than for other stations. The results indicate that 40, 50, 20, and 55 stations were adequate to represent rainfall with 15% average error in the regions of Bandar Lengeh, Bandar Abbas, Hajiabad and Minab, respectively.

This study used quantifying factors affecting desertification based on the Iranian model of desertification potential assessment (IMDPA) to assess the current status of desertification in Bordekhun region, Iran. Bordekhun region has an area of 214.11 km2 and is located near the city of Daiyer in Boushehr province. First, a working unit map of the region was selected as the basic map for evaluation of factors and indices of interest. Regional conditions for the five criteria of climate, wind erosion, water, soil, and vegetation were calculated as essential for the study of desertification intensity. The scores for the indices were determined using IMDPA; for each index, a map was prepared employing the calculated weighting. A qualitative map of the criterion was obtained using the geometric mean of indices related to each criterion. A map of current desertification potential was then created for the study area by combining the layers produced for each criterion, determining their geometrical means, and classifying the resultant map. Analysis of the study criteria showed that climate was rated high with a quantitative value of 3.15, wind erosion was high with a value of 2.87, water was medium with a value of 1.77, soil was high with a value of 2.66, and vegetation was medium with a value of 2.37. The results showed that of the total area, 49.12% is classified in the high desertification class, 48.9% is in the moderate class and about 0.99% is not classified. The quantitative value of desertification intensity on the basis of the five criteria for the entire study area was desertification map (DM) = 1.55, which is indicative of the average desertification intensity in the region. The study area is located such that it has the potential for severe desertification. Climate was found to be the dominant criterion and plays an important role in desertification.

The present study examined year-to-year variations in areas affected by drought during a period of 39 water years in Iran. Ninety-five meteorological stations were chosen to provide near-continuous long term records, although some data was missing (less than 10%). The missing data points were estimated using a linear correlation method between the reference station with the missing data points and a neighboring station that had a complete record. At all stations, the standard index of annual precipitation (SIAP) was calculated for water year (sum of precipitation from October 1 to September 31). The geo-statistical method of weighting moving average (WMA) was applied to a 2×2 km grid network map of Iran and the geographical distribution of SIAP was calculated and displayed. From this, the percentage of area affected by severe, moderate, and mild drought was computed for each year; the frequency of drought was analyzed by severity and the behaviors of the most extensive historical droughts were determined. The results showed that: a) the maximum frequency of severe drought was 5.1 times and moderate drought was 23.1 times per 100 years; b) the most extensive droughts (more than 80% of the country) occurred during 1970-1971 (82.21%), 1988-1989 (92.05%), and 1999-2000 (96.27%); and c) drought spread in Iran beginning from the northwestern and southeastern regions, gradually extending to the central regions.

The application of organic amendments can be an appropriate solution to reclaim and improve physical properties of saline-sodic soils. In this research, an experiment was performed under greenhouse conditions to study the effect of amendments to the physical properties of loamy saline-sodic soil. The five treatments were control (without amendment), municipal solid waste compost (MC), vermicomposting (VC), poultry manure (PM), and gypsum powder (G). They were carried out in a completely randomized design with three replications. Each treatment comprised 10 ton/ha of the specified soil added to the soil. The results showed that soil amendments decreased bulk density (p<0.05) and increased mean weight diameter of aggregates (MWD) (p<0.05) over the control. The saturated hydraulic conductivity (Ks) for the G treatment was significantly higher than other treatments (p<0.05). The addition of amendments significantly increased the Sgi index, which is defined as the slope of the retention curve at its inflection point, but the Sgi index between the G and MC treatments was not significant (p<0.05). In addition, plant available water content (PAWC) increased significantly (p<0.05) for organic amendments over the G and control treatments, and a maximum value was observed for the PM treatment. The positive effects of the amendments showed that the application of organic and/or inorganic amendments can be recommended for saline-sodic soil to improve soil physical quality.

Drought monitoring is a fundamental component of drought risk management. It is normally performed using various drought indices that are effectively continuous functions of rainfall and other hydrometeorological variables. In many instances, drought indices are used for monitoring purposes. Geostatistical methods allow the interpolation of spatially referenced data and the prediction of values for arbitrary points in the area of interest. In this research, several geostatistical methods, including ordinary kriging (OK), indicator kriging (IK), residual kriging (RK), probability kriging (Pk), simple kriging (SK), universal kriging (UK), and inverse distance weighted (IDW) methods were assessed for the derivation of maps of drought indices at 12 climatic stations in southern Iran. Data regarding monthly rainfall, temperature, wind, relative humidity, and sunshine of three periods 1985, 1995, and 2005) were taken from 12 meteorological synoptic stations and distributed areas. Based on the used error criteria, kriging methods were used for spatial analysis of the drought indexes and were selected as the best method. Results also showed that the lowest error (RMSE) is related to the kriging method. The results indicated that IK with tree frequency is more appropriate for the spatial analysis of the RDI index, and the Pk and SK methods are more appropriate for the spatial analysis of the SPI index. The kriging methods mean errors (RMSE) selected years for RDI and SPI index respectively are 0.85 and 0.84. In several cases, the “moderately dry” class received a more critical value by RDI. The results showed that by utilizing the ET0, the RDI can be very sensitive to climatic variability.

Drought is a major environmental disaster in many parts of the world. Knowledge about the timing, severity and extent of drought can aid planning and decision-making. Drought indices derived from in-situ meteorological data have coarse spatial and temporal resolutions, thus, obtaining a real-time drought condition over a large area is difficult. This study used advanced very high resolution radiometer (AVHRR) images to evaluate the efficacy of NOAA-AVHRR data for monitoring drought in Iran for the 1997-2005 (March-July) time period. Ten-day maximum normalized difference vegetation index (NDVI) maps were produced and a vegetation condition index (VCI), vegetation health index (VHI) and temperature condition index (TCI) for the same period was calculated. Precipitation data from 47 synoptic meteorological stations was collected to calculate the standardized precipitation index (SPI) as a meteorological drought index. Analysis and interpretation of these maps revealed that the spatial extent of the satellite-derived drought-indices and SPI generally confirm each other. Based on the statistical analysis, higher correlations were found among the satellite-derived indices while lesser or no relationships were found between the satellite-derived indices and SPI. The results revealed that high correlations were found among TCI and VHI, VCI and VHI in dry, normal, and wet years 0.662 to 0.813). Iran suffered from severe drought during 1999-2001.The results of remotely-sensed indices and the SPI index for 2002-2005 most of the region show that it experienced normal conditions.