Changes in drought trends in Zhangjiakou due to global climate change

Based on monthly precipitation and temperature data of Zhangjiakou from 1959 to 2017, drought index was determined and used to estimate annual and seasonal drought trends as well as trends within vegetative and non-vegetation growth periods. The results were as follows. 1) Annual average precipitation and precipitation in summer and winter significantly increased. Precipitation in spring, autumn, and vegetative and non-vegetative growth periods increased, although the trend of change was not significant. 2) Annual average temperature and temperature in spring, summer, and autumn showed a significant increasing trend, while that in winter as well as vegetative and non-vegetative growth periods showed a non-significant increasing trend. 3) Annual average drought index and drought index in spring, autumn, and vegetative growth period showed a non-significant increasing trend. 4) Overall precipitation, temperature, and drought index did not show a significant change across different timescales, including annual average and values in spring, summer, autumn, and winter. 5) The greatest effect of precipitation and temperature on drought trend was observed in winter. 6) Drought in summer, winter, and non-vegetative growth period showed a non-significant decreasing trend. Although precipitation and temperature in the study area showed increasing trends across different timescales, drought showed an overall increasing trend, because increasing temperature led to excess evapotranspiration, ultimately increasing precipitation. The degree of change in precipitation and temperature varied across different periods, resulting in diverse degrees of drought.