Journal of Spatial Analysis

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The correct management in natural ecosystems is not possible without knowledge of the health in its sectors. Vegetation is the most significant sector in ecosystem that has important role in its health. Resilience is one of the defining features of health vegetation The term resilience was first introduced in the study of ecological systems and demonstrates the ability of the ecosystem to maintain its performance in the face of environmental disorders. A resilience-based system is not only equipped with a disorder adjustment mechanism but also has the potential to benefit from changes in a way that lead to creating an opportunity for development, innovation, and updating. Therefore, when a change occurs, the resilience provides the needed conditions for restarting and reorganization. If this goes beyond disturbing forces, the system will have the power to return to the maximum vegetation density with the least erosion effects, otherwise the system will be vulnerable to the change that was created and could already be controlled.
This research was done in part of North east of South Khorasan province (arid climate) with the aim of quantifying vegetative resilience on behalf of ecosystem health in response to drought occurrences and long-term precipitation changes, as environmental disturbances. Therefore first, using daily precipitation data from 15 meteorological stations around the study area, their annual precipitation was extracted and was standardized by Standard Precipitation Index (SPI) over the course of thirty years (1986 - 2015). Then, the SPI index data in 15 stations were interpolated by ArcGIS software based on Inverse Distance Weighted (IDW) method and dry, wet and normal years was estimated in the study region for each year. On the other hand, from archive of satellite images of Landsat 5 and Landsat 7, an image was created for each year in study period, between 15 June and 15 July, with permanent coverage at the best of growth. Following the necessary corrections for satellite images, the average Transformed Normalized Difference Vegetation Index (TNDVI) was obtained of each image by ENVI software. Finally, effected of precipitation changes on mean TNDVI was assessed and vegetation resilience was stabilized whit selected of sever time period samples based on four effective parameters (Amplitude, Malleability, Damping and Hysteresis).

Comparison of annual precipitation variations in the thirty-year time series (1986 -2015) indicated two approximate wet and dry periods in study area. The wet period is related to the first fourteen years of the time series (1986-1999) and the dry period is related to the last sixteen years (2000-2015). In this term, severe precipitation incidents with different intensities were occurred in the study area including one case of very intense precipitation (1986), one case of intense precipitation (1991) and two cases of moderate precipitation (1996 and 1992). Also, four drought incidents were occurred including one case of intense drought (2001) and three cases of moderate drought (1987, 2006 and 2008). All precipitations (wet years) are related to the first half and most droughts are related to the second half of the studied period. In this study for fixing of vegetation resilience in study area and for calculating of its parameters, In addition to the thirty-year time series selected sever time sections. in the whole study series (1986 - 2015), maximum of mean TNDVI (49.37 %) was in 1986 (reference), the lowest mean TNDVI (43.58%) was in 2010, The year effect of the decrease precipitation and drought, and mean TNDVI in 2015 was 44.28 %. Amount of parameters amplitude, malleability and damping are respectively 5.79, 0.7 and 5.09, and hysteresis was zero (%). The result of this case showed that the vegetation has moved towards the reference state (Resilience) but has not reached to amount of reference vegetation. The most specific cases for vegetation resilience happened from 1986 to 1996 (wet period) and 2003- 2009 time sector (dry period). In the first time section amount of amplitude and malleability were 0.64 %, damping was zero and hysteresis was 0.25%. The result of this case showed that not only the vegetation was returned to the reference state but also was increased to the reference (Cross reference).So despite the reduced rainfall and occurrence of sever occurrences of drought in dry period, hysteresis parameter (0.05 %) observed in 2003- 2009 time sector too that confirmed clearly vegetation health in study area whit dry climate. 

Awareness of the health status of the vegetation and its response to long-term precipitation changes and environmental disorders, such as drought occurrence, ensure the success of the managerial plans for renewable natural resources. The present study is the second study on quantifying the vegetation resilience and the first study under dry climatic conditions in Asia (an average annual precipitation of 160 mm) conducted in Iran by calculating four factors related to resilience, and is the first study that has presented the factor hysteresis in the calculations. Despite continuous of difficult condition, the native vegetation of the study area has been able to return the reference state not only by resolving the disorder relatively, but also it has experienced hysteresis stage. A set of quantitative calculations showed despite reduced annual precipitation and drought events, vegetation has been able to maintain its resilience, which indicates the health of the vegetation in the studied ecosystem. With the presence of such amazing protective and consistent mechanisms in the vegetation of arid regions, it is possible to maintain and restore these regions by proper managerial plans.

 

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Potential dangers of drought in Shadegan wetland and Identify areas affected by dust from it
 
Introduction
Shadegan wetland is located at the end of Jarahi watershed. This wetland is one of the most important international wetlands registered in the Ramsar Convention, which is currently undergoing ecological changes and is still on the red list of the Montero Ramsar list. This wetland is extremely important due to its high biodiversity and various functions such as flood control, air conditioning and soil erosion control, habitat of various plants and animals and providing livelihood for a part of human societies. One of the most important functions of the wetland, according to the findings of the present study, is the important role of Shadegan wetland in preventing the production and control of fine dust. There are 143 wetlands in Iran, of which 25 are registered in the Ramsar Convention. Shadegan wetland is one of the wetlands of Ramsar Convention, which in the last decade, a large area of ​​it has become dry and has become a center of dust. In this research, it is important to know that in case of drying of Shadegan wetland, which areas in which seasons will be more affected by dust due to atmospheric currents.
Data and methodology
In this study, the boundary of the wetland was determined based on the highest water advance line during a 30-year statistical period (1988-2017). According to satellite images, the border of the wetland has been determined to be about 164,000 hectares based on the rainiest year and month. Wetland area changes were used to monitor the water level of Shadegan Wetland through Landsat TM, ETM + and OLI satellite data from 1998 to 2017 in the period of June. Three stages of preprocessing, processing and post-processing were performed on the images and supervised classification by support vector machine (SVM) method was used and the images were classified into three classes of water, vegetation and without cover or soil. On the other hand, the classification accuracy for the images was calculated using two indicators, overall accuracy and kappa. To calculate the dry area of ​​the lagoon, floor changes without cover were calculated. The most important cities around Shadegan wetland, which in case of wetland drought may be most affected by wetland dust due to proximity and proximity, and have socio-economic importance and the center of the province and port status, were identified. In this study, the cities of Ahvaz, Abadan and Mahshahr were identified and studied as areas affected by wetland dust during drought. In order to study the role of drying of Shadegan wetland in the dust of the surrounding areas, seasonal and annual dust mites were prepared and drawn. Data on the direction and speed of hourly winds along with the dust were used. Then, using WR-PLOT software, in addition to the annual long-term total rainfall, the seasonal distribution of the direction and speed of events was extracted and the rainfall related to each season was plotted and analyzed, and areas affected by drought in different seasons of the year. Wetlands with greater impact were identified.
 
Result
The trend of 30-year changes in the soil cover of Shadegan wetland is increasing in total, so that according to the freshwater area of the wetland, which was obtained in this study 164 thousand hectares, 22960 square kilometers has been added to the dry area of the wetland during these 30 years. The largest soil area of the wetland in 1994 was about 87.4% of the total area of the wetland. The lowest soil area of the wetland in 1998 was about 19%. Sugarcane projects have entered the wetland from the north of Shadegan Zahab Wetland since 2002, but due to widespread drought, it has not been able to increase vegetation and reduce the soil area of the wetland.
During the long-term statistical period, spring is the predominant period of pollination in Ahvaz western synoptic station and secondarily in the northwest. The southeast direction is of third importance, but nevertheless, the dryness of the north and northeast parts of the wetland can affect the south and southeast of Ahvaz in this season in Abadan synoptic station. Drought on the west side of the wetland is not a threat to the city of Abadan. In Mahshahr synoptic station, the predominant direction of long-term seasonal rainfall is northwest. In case of drought, Shadegan wetland will be affected from the northwest. During the long-term statistical period, the summer season was dominated by dust and affected in three stations, such as the spring season, with the difference that in this season, dust is more abundant. During the long-term statistical period, autumn is the predominant direction for flowering and is affected in three stations such as spring and summer, but in this season, the southeast and south directions are more intense and frequent than spring and summer.
During the long-term statistical period, winter is the predominant period of pollination in Ahvaz synoptic station, west and secondarily, northwest. The southeast and south directions are of third importance, but in this season, the southeast and south directions are more intense and frequent than other seasons. In this season, due to the expansion of the westerly wind to the lower offerings, unstable atmospheric systems enter Khuzestan from the south and southeast and bring dust with them from areas such as western and southern Iraq and northern Saudi Arabia, and to the southeast. Northwest and passing through the dry parts of the lagoon and the active dust center of the southeast of Ahvaz, the metropolis of Ahvaz will face problems caused by dust in this season. Due to the cold weather and the inversion phenomenon, the dust of this season, which is associated with wetland and inland resources, has a greater impact on the field of view and causes great damage to the equipment and infrastructure facilities by subsiding on the city of Ahvaz.
Conclusion
Drying of wetlands due to various climatic or human factors can lead to increased dust activities. When a wetland dries out, the salts that settle in it become sources of dust. Wetland fine-grained sediments with air velocity less than the erosion threshold due to small diameter and large volume enter the air streams and are dispersed in the air. Active dust centers in the southern half of Khuzestan province have the largest area in the whole country. Shadegan wetland is bounded on the north by the dust center of the south and southeast of Ahvaz with an area of ​​185043.3 hectares and on the west by the center of the south of Horalazim and north of Khorramshahr with an area of ​​258916.4 hectares and on the east by the dust center of Mahshahr - Omidieh Hindijan with an area of ​​254654.4. Shadegan wetland joins the southeastern center of Ahvaz in case of drought from the north and northeast, as if parts of it, known as Hor Mansoureh, have become part of the southeastern center of Ahvaz in the last decade due to several droughts. Is. From the west, parts of it are connected to the dust center north of Khorramshahr and join it if the drought continues. It is connected to Mahshahr-Omidieh and Hindijan centers from the east. In recent years, parts of the wetland and dust centers have overlapped. If the wetland continues and dries, for natural and managerial reasons, more parts of the wetland will dry up and become dust centers and affect important population, political and port cities of Khuzestan Data and will face irreparable social and economic losses.
 
Keywords: Dust center, dust, wind direction and speed, Shadegan wetland, Right of water
 

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In the study of the trend of dust storm index, the results showed that the study period of 2003-2007 in Semnan province has an increasing trend and has shown significant changes in the 95% confidence range, but the lack of significant changes in the last decade shows the effects of various events. In cross-cutting decisions in the field of dust in the region. The zoning of the DSI index changes in different regions of the province in a 15-year statistical period indicates that from the west to the east of the province due to the increase in the frequency of stormy days with moderate dust (MDS), dust has increased. The correlation between drought and DSI index in Semnan province showed that although DSI index increased during the period under analysis with increasing drought intensity and its correlation with drought during the 15-year period was not significant, but the pattern of DSI index is consistent with It is the pattern of the drought process. According to the results, it can be acknowledged that the dust situation has always been affected by climate, but the relationship between drought and the DSI index has always fluctuated with respect to droughts and wetlands. However, different climatic parameters are different and their impact is different. In addition to human activities, the main role of wind in the amount of dust or the existence of another source of dust should be considered.