Analysis of land use changes in the middle Taleghan watershed during a thirty year period

In Iran, as in other countries, social and economic factors have led to land use changes depending on regional conditions. The Taleghan watershed, due to its proximity to population centers such as Tehran and Karaj, construction of the Taleghan Dam in 2001, and becoming a tourist center, has undergone significant changes. Many studies have been conducted to evaluate land use changes in this area, but these studies have investigated changes only until the time of dam water withdrawal in 2005 or until 2016 at most. Thus, this research investigates and analyzes land use changes in the Taleghan watershed over a period of thirty years (1987-2017).

The study focuses on land use changes in the middle Taleghan watershed. A land use map was prepared for the last thirty years (1987, 1998, 2008, and 2017) using Landsat satellite imagery. The hybrid classification method (a combination of supervised and unsupervised methods) was used, and accuracy was measured using Kappa and overall accuracy, yielding acceptable results in percentages. The T index was used to calculate land use changes.

The study shows that the abandoned dryland area (12.08%) is the largest after pasture land use (71.06%). The area of villa construction increased, while the garden area decreased over the thirty-year period. The T index calculation reveals that barelands experienced the most changes during the thirty-year period.

Spatial patterns of land use changes were estimated using spatial statistics and the calculation of the share of changes in various land uses. Location quotients were used to analyze the data, and it was calculated for the land uses that experienced the most changes in each sub-watershed in 1987, 1998, 2008, and 2017. The results of the LQ show that the rangeland area was almost constant during the period of 1987-2017. The areas of irrigated and rainfed agriculture fluctuated due to emigration and immigration during this period. The area of residential land also increased significantly due to the construction of villas and promenades around the lake by indigenous and non-indigenous people. Investigating the variations of the spatial pattern of different land uses revealed that the most changes occurred in the sub-watershed around the dam lake and the main river.