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This paper reports a comprehensive study on the observed and projected spatiotemporal changes in mean and extreme climate over the arid region of northwestern China, based on gridded observation data and CMIP5 simulations under the RCP4.5 and RCP8.5 scenarios. The observational results reveal an increase in annual mean temperature since 1961, largely attributable to the increase in minimum temperature. The annual mean precipitation also exhibits a significant increasing tendency. The precipitation amount in the most recent decade was greater than in any preceding decade since 1961. Seasonally, the greatest increase in temperature and precipitation appears in winter and in summer, respectively. Widespread significant changes in temperature-related extremes are consistent with warming, with decreases in cold extremes and increases in warm extremes. The warming of the coldest night is greater than that of the warmest day, and changes in cold and warm nights are more evident than for cold and warm days. Extreme precipitation and wet days exhibit an increasing trend, and the maximum number of consecutive dry days shows a tendency toward shorter duration. Multi-model ensemble mean projections indicate an overall continual increase in temperature and precipitation during the 21st century. Decreases in cold extremes, increases in warm extremes, intensification of extreme precipitation, increases in wet days, and decreases in consecutive dry days, are expected under both emissions scenarios, with larger changes corresponding to stronger radiative forcing. [ABSTRACT FROM AUTHOR]

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This study examines the expansion of drylands and regional climate change in northern China by analyzing the variations in aridity index (AI), surface air temperature (SAT), precipitation and potential evapotranspiration (PET) from 1948 to 2008. It is found that the drylands of northern China have expanded remarkably in the last 61 years. The area of drylands of the last 15 years (1994-2008) is 0.65×10 km (12%) larger than that in the period 1948-62. The boundary of drylands has extended eastward over Northeast China by about 2° of longitude and by about 1° of latitude to the south along the middle-to-lower reaches of the Yellow River. A zonal band of expansion of semi-arid regions has occurred, stretching from western Heilongjiang Province to southern Gansu Province, while shifts to the east of semi-arid regions in dry subhumid regions have also occurred. Results show that the aridity trend of drylands in northern China is highly correlated with the long-term trend of precipitation and PET, and the expansion of semi-arid regions plays a dominant role in the areal extent of drylands, which is nearly 10 times larger than that in arid and subhumid regions. [ABSTRACT FROM AUTHOR]