تحلیل همبستگی فضایی تغییرات پوشش گیاهی با ارتفاع رواناب در حوضه آبریز گرگانرود

Spatial Correlation Analysis of Vegetation Changes with Runoff Height in Gorganrood Watershed















Summary

In recent years, flood phenomenon has been one of the hydroclimatic events and one of the most serious natural hazards that has threatened human societies. Indiscriminate exploitation of forests and pastures and land use change and their transformation into unsuitable agricultural lands, along with the indiscriminate construction of residential areas, have caused an increase in floods. Therefore, the flood phenomenon is very important. Therefore, the present study was conducted with the aim of analyzing the spatial correlation of changes in vegetation cover with the height of runoff in the Gorgan River watershed in a 21-year period. For this purpose, from the data of slope, soil type, land unit and land use to prepare the hydrological response unit and Landsat images of different years (2000-2021) to investigate changes in vegetation density using the NDVI index in each of Hydrological response units are used. In this regard, 72 hydrological response units were prepared as basic units in the study area. Also, the height of the runoff was calculated by the SCS method in each of the hydrological response units using the criteria of rainfall height, soil hydrological group, vegetation, land use type and soil texture, so that the cities of Agh Qola, Simin Shahr and Gomish Tepe and the Gorganrood River in the height of the runoff There are many. The results of the analysis of 78% of the spatial correlation between the height of runoff and the density of vegetation showed that the agricultural and garden lands in the plains have increased significantly, while the density of forest and pastures has decreased in the 21-year period. This factor is caused by human activities such as the destruction of forests and pastures and the cultivation of these lands and the development of cities, the height of the runoff has increased. While in the highlands, due to more infiltration, despite the decrease in vegetation density, the runoff height is also low.









Key words: flood, Gorgan River watershed, hydrological response unit, NDVI, SCS.





Introduction

Climate change has had a significant impact on the earth (Miller and Hutchins, 2017, 350), including increasing the change in the hydrological cycle and increasing the probability of extreme weather events such as droughts and floods. (Bates, 2008, 86). Flood is one of the most destructive natural hazards with high occurrence frequency all over the world and has a great impact on the population (Akoko et al., 2020, 120.; Zhou et al., 2016, 2373). For this reason, it has recently increased in areas that have no history of such events such as heavy rainfall followed by floods (Hetiarchichi et al., 2018, 2050). The change of land use due to urbanization has increased the sensitivity to floods (Kaspersen et al., 2015, 22). Because urbanization is largely associated with the destruction of soil and vegetation, which are important factors for limiting surface runoff (Pradhan and Pokharel, 2017, 60). In this regard, many internal and external studies have been conducted in recent years. Many rivers in America (Corkey Fox et al., 2022), Brazil (Verlitis et al., 2022) and China (Guan et al., 2021) are involved in flood risk. Lovell et al.(2014) in a research analyzed the flood extraction model and factors affecting the flood in Perlis, Malaysia. Using remote sensing data and geographic information system, they introduced three geological factors, land use and slope as the most important factors causing floods in the studied area. In a research, Satishkumar et al. (2017) estimated the amount of runoff in North India using the SCS-CN method in a GIS environment. Based on the obtained results, they confirmed the use of this model and method to estimate runoff in their study area. Savido (2018) studied the structure of hydrological response units in order to estimate the runoff curve using geographic information system. In order to extract hydrological response units, they used three characteristics of soil permeability, land cover and river drainage capacity according to the geomorphological characteristics of the basin. In recent years, our country has seen frequent floods. Safari et al. (2013) evaluated the vulnerability of urban areas against flood risk using geographic information system and fuzzy logic in Tehran's third district. In the conducted research, the boundaries of the river channels, the structure, direction and width of the communication network, land use, the combination of worn and new texture, the density of buildings and the overall capacity of the area's flood control as the necessary criteria to evaluate the vulnerability in against the maximum watershed of the basin for the return period of 25 and 50 years were used. Kanavati et al.(2013), using information layers related to slope, profile and planimetric curvature, height, drainage density, distance from waterways, landforms and land use, identified the areas with the highest risk of flooding in Farahzad basin with determined the use of fuzzy model. The results showed that the areas with very high flood risk were in the lower reaches of the basin and corresponded to the main valley of Farahzad, which includes slopes of 20-40%. Natagi et al. (2016), the results of monitoring vegetation changes in Qeshm Island using Landsat images in a 13-year period (1380-1393) showed that during the study period, 21% of the area was mangrove forests and 60% of agricultural lands and The natural cover inside the island has been added. Also, the results of Nikpour et al.'s research (2017), the increase in normalized plant diversity index vegetation in Ilam province in a 17-year period (2000-2016) due to the increase in rainfall and humidity and the increase in agriculture dependent on the Simreh dam and rivers It is watery. They concluded analysis