Qualitative Study of Vegetation Resilience in Response to Long-Term Precipitation Changes (Case Study: Part of the Namakzar-e khaf Watershed Basin, South Khorasan Province)

Vegetation is one of the most important ecosystem components that is constantly being adapted or altered to the final balance under the influence of environmental factors. One of the most important signs of the health of the vegetation and the consequent ecosystem health is its ability to resilience after the removal of environmental turbulences. Although vegetation in arid and semi-arid areas has different methods for dealing with destructive forces, the continuity of these factors can disrupt the ability of vegetation to return to its original state after eliminating the destructive factors. The result will be the disease and, ultimately, the destruction of the ecosystem. Therefore, detection, prediction of ecosystem changes over time and management of such changes is of great importance. This research was carried out in the Namakzare Khaf watershed basin in South Khorasan Province with the aim of studying and qualitative determining of ecosystem resilience vegetation to severe changes in long-term precipitation and drought as environmental turbulences. For this purpose, the standardization of annual rainfall during the thirty-year period and the determination of the duration and severity of dry, wet and normal periods was performed with SPI method and then the ecological resilience of the vegetation was examined qualitatively based on the mean plot and Transformed Normalized Difference Vegetation Index (TNDVI) variance. These changes were studied using landsat satellite images in the final growth season of vegetation. Results indicate the mean ability to resilience and restore vegetation in the study area after the elimination of severe to medium droughts. According to the results, the ecosystem health of the studied area was confirmed on the basis of vegetation resilience, despite being located in dry land and facing severe droughts with continuity of two years and continuation of rainfall reduction compared to the mean for 6 years.