Abstract:  In this study, the groundwater level at four observation sites in the lower reaches of the Tarim River was monitored, and the values of groundwater evapotranspiration were estimated. The purposes of the study were to analyze the fluctuations of groundwater level and the groundwater evapotranspiration (ET_g) as well as their main affecting factors. The results showed that:   ① A drawdown of groundwater level occurred holistically at the four observation sites before implementing the project of ecologic water conveyance; after implementing the project from July 21 to August 12, however, the groundwater level was in a steady rising trend. There was a diurnal-nocturnal fluctuation of groundwater level during the study period;   ② The curve of ET_g was unimodal, ET_g began to rapidly increase from 08:00, maintained at a high level from 12:00 to 16:00, and rapidly decreased after 18:00. The highest value appeared at 14:00 local time;  ③ ET_g varied significantly with different vegetation types and coverage, and was also affected by groundwater depth;   ④ Solar radiation, temperature and vapor pressure deficiency were the main factors affecting the daily variation of groundwater evapotranspiration in the lower reaches of the Tarim River, and the effect of wind speed on it was not significant.

Key words: groundwater evapotranspiration, groundwater level, desert riparian forest, lower reaches of the Tarim River