Abstract: This paper analyzes the temporal evolution characteristics of precipitation amounts, precipitation days, and precipitation intensity of light rain (0.1-9.9 mm per day); moderate rain (10.0-24.9 mm per day); heavy rain (≥ 25.0 mm per day) in summer during 1963-2014 in the east of northwest China and further discusses their contributions to total precipitation amounts, precipitation days, and precipitation intensity in summer. Results show that:(1) Precipitation was mainly concentrated in summer over the east of northwest China, and the percentages of summer precipitation amount (days) in annual precipitation amount (days) increased rapidly as the level of precipitation rises. The heavy rain amounts (days) in summer accounted for 72.15% (69.19%) of annual heavy rain amount (days). (2) There was an abrupt change around 1996 in the precipitation amounts and precipitation days of different levels of precipitation. Significant short periodic vibrations of 2-3 years in the precipitation amount, days and intensity of different levels are revealed by conducting wavelet analysis. (3) There were similar interannual and interdecadal variations between total summer precipitation amounts and moderate/heavy rain amounts with correlation coefficients higher than 0.8. Affected by moderate and heavy rain amounts, summer precipitation amount increased in the central part of Gansu and the whole Shaanxi Province while decreased in southern Gansu and central Inner Mongolia. The changes in total precipitation days were consistent with the changes in light rain days, which decreased over the whole eastern part of northwest China. And the increase of total precipitation intensity was due to the increase of heavy rain intensity.

Key words: east of northwest China, summer, precipitation, temporal variation