Abstract:  

The study of Land Use/Cover Change (LUCC) and its dynamics is crucial for human existence and sustainable development. LUCC simulation is the main content and effective method in LUCC research and time span is one of the most important parameters in the simulation process, and thus its effect on the simulation accuracy needs to be further studied. In order to explore LUCC simulation accuracy at different time spans, we took Sidaohezi Town of Manas River Basin in Xinjiang, China as the study area. Seven land use maps were created from remote sensing images (MSS images in the 1975, M images in 1985 and 1995, ETM images in 2000, 2005 and 2010, and OLI images in 2015) and the land surfaces were classified into six land cover categories: cultivated land, woodland, grassland, water area, construction land and unused land. Then the land use transition probability during four different periods (1975—1995,1985—2000,1995—2005 and 2005—2010) were used to establish the CA-rkov model to simulate land use in 2015 using long-term (20-ears),medium-term (15-and 10-years) and short-term (5-years) intervals respectively. he simulation process was completed by the CA-arkov module in IDRISI software. Finally, our simulated land use maps for 2015 (R₁, R₂, R₃, R₄) were compared with the real land use map in 2015 (R), and the Total Figure of Merit (TFOM) indexes were used to evaluate the model's accuracy. he results showed that from 1975 to 2015,cultivated land and grassland were the dominant land use types in Sidaohezi Town. During the study period, cultivated land and construction land expanded rapidly, whereas forest land, grassland and unused land have been greatly reduced, and the water area has experienced a slight increase from 1985 to 2000.Throughout the study period, he increase of cultivated land and decrease of grassland and woodland were the most significant features of LUCC. compared the simulated results with real land use map in 2015,five components of agreement and disagreement were detected as S₁,S₂,S₃,S₄ and S₅The TFOM indices of 20-, 15-, 10- and 5-years intervals were 70.35%,69.18%,76.32% and 88.00% respectively. It was indicated that smaller time intervals produced higher accuracy. The time span of 5-years was the optimum time interval to simulate the land use change of Sidaohezi Town from 1975 to 2015.This study provided a scientific basis for the selection of time interval in land use change simulation. Moreover, the simulation accuracy depends not merely on the land use transition probability within a certain period of time, but the local land policies and social development characteristics in the same time should also be considered.

Key words: Manas River Basin')">">Manas River Basin, land use and cover change, CA-Markov, time span