Changes of daily climate extremes in Loess Plateau during 1960–2013

Abstract

Analysis of changes in twelve indices of extreme temperature and eleven of extreme precipitation at 64 meteorological stations in Loess Plateau during 1960–2013 revealed 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 ice days and the number of frost days were statistically significant, but a decreasing trend of the diurnal temperature range was not significant. At a large proportion of the stations, patterns of temperature extremes were consistent with warming since 1960. Warming trends in minimum temperature indices were greater than those relating to maximum temperature. Warming magnitudes were greater on the southern and northern Shanxi Loess Plateau, the eastern Gansu Loess Plateau, and the Erdos Plateau than on the middle part of the eastern Shanxi Loess Plateau, the northern Shaanxi Loess Plateau and the Guanzhong Plain, as confirmed by the decrease of the regional trend from north to south. Changes in precipitation extremes were relatively small, and only the regional trends in consecutive dry days and simple daily intensity index were significant. These trends were difficult to detect against the larger inter-annual and decadal-scale variability of precipitation. On the whole, the number of rainy days increased on the northern Loess Plateau, but the extreme precipitation events had decreased in the whole region. The spatial distribution of temporal changes of all extreme climate indices in Loess Plateau reflects the general climatic complexity and the influence of topography. Analysis of large-scale atmospheric circulation changes revealed that a strengthening anticyclonic circulation, increasing geopotential height, weakening monsoonal flow, and vapor transportation over the Eurasian continent have contributed to the changes of climate extremes in the Loess Plateau.