Abstract: Climatic characteristics of rainfall, transpiration, evaporation and temperature were summarized and analyzed in arid and semi-arid areas in the past 50 years. A full-scale extreme rainfall test of capillary barrier cover was carried out in a landfill in Northwest China to verify the impermeability with extreme rainfall accidents. Long-term anti-seepage performance of the cover was analyzed. The high-risk meteorological conditions of anti-seepage in arid and semi-arid areas were identified and screened. The meteorological mechanism of high-risk permeable meteorological period causing percolation was revealed. Results show that: (1) The precipitation in arid and semi-arid climate area of Northwest China is more from April to November, and less from December to April of the next year, with dry winter and wet summer. It is beneficial to the storage and release of water. (2) The threshold value of extreme accidental continuous heavy precipitation in the northwest non humid area is 56.1–118.5 mm. The cumulative rainfall of field cover extreme rainfall test is 194.85 mm, and the soil layer storage is 148.22 mm. With the condition of extreme accidental continuous heavy rainfall in this area, the capillary barrier cover can meet the anti-seepage standard. (3) In the arid and semi-arid climate region, August to November is the high-risk meteorological period for capillary barrier cover, followed by November to December. The possibility of percolation is the lowest from January to July. In the anti-seepage design of soil cover and the management of landfill, August to November can be regarded as a key meteorological period for verification and control.

Key words: landfill, capillary barrier cover, long-term service, extreme rainfall, anti-seepage design, high-risk permeable meteorological period