Abstract: The 1961-2006 inter-annual and inter-decadal variations of potential evapotransporation and drywet index in Yamdok Tso Lake Basin of Tibet were analyzed by PenmanMonteith model, with the meteorological factors affecting the variation of the drywet index identified. The results indicated that in 1961-2006, the annual potential evapotranspiration was decreased with a rate of 13.1 mm·10 a^-1. The seasonal potential evapotranspiration also had a decreasing trend, with the maximum in winter and the minimum in summer. Though the annual and seasonal variations of the dry-wet index were not obvious, the dry-wet index itself increased significantly in 1981-2006, both at the annual and the seasonal scales except in winter. The maximum increasing rate occurred in summer, which was attributed to the increased precipitation and decreased evapotransporation in this region in the recent 26 years. Except that in the 1980s, most of the average annual drywet index was higher, with the maximum in the 1990s. The climate changed toward an obvious warm-wet type, with dry-wet index increasing. The obviously increased dry-wet index could be mainly attributed to the obviously increased precipitation and temperature and the decreased mean daily range of temperature, together with the obviously declined sunshine hours which also played an important role in the dry-wet index. In recent years, the water level of the Yamdok Tso Lake ascended obviously, which was resulted from the increasing precipitation, temperature, and snow-melting.

Key words: Pig manure, Compost, Oxygen consumption rate, Ventilation