Changes of daily climate extremes in northwestern China during 1961-2008

Based on the daily maximum and minimum surface air temperature and precipitation records from 129 meteorological stations in the northwestern China during 1961-2008, the changes in twelve indices of extreme temperature and eleven of extreme precipitation are analyzed to reveal the spatial and temporal distributions of indices of climate extremes. That indicates statistically significant increases in the temperature of the warmest and coldest nights, in the frequencies of extreme warm days and nights and in the growing season length. Decreases of the diurnal temperature range and the number of frost days were statistically significant, but a decreasing trend of ice days was not significant. At a large proportion of the stations, patterns of temperature extremes were consistent with warming since 1961. Compared with many other parts of the world, the northwestern China can be characterized by the decrease of the DTR with greater magnitude, whereas the warming magnitudes of other indices are the lowest. Warming trends in minimum temperature indices were greater than those relating to maximum temperature. In terms of the distribution, the warming trend in Qaidam basin and Tienshan mountain is greater than that in Qinlan mountain, western inner Mongolian plateau and loess plateau, which can be also supported by the decrease of regional trend from west to east. Changes in precipitation extremes were relatively smaller, and only the regional trend in consecutive wet days, extremely wet day precipitation and maximum 1-day precipitation were significant, as these trends are difficult to detect against the larger inter-annual and decadal-scale variability of precipitation, whereas the increase of extreme precipitation events is common in study region. In addition, the significant decrease of maximum number of consecutive dry days mainly happened in Qaidam basin. The spatial distribution of temporal changes of all extreme climate indices in northwestern China reflects the general climatic complexity and the influence of topography.