Trends in temperature and extreme temperature over the Beijing-Tianjin-Hebei Metropolitan Region During 1957-2009

Study on change of weather and climate extremes has become an important aspect in modern climate change research. Based on the data of daily temperature from year 1957 to 2009, the spatial and temporal features of trends of extreme climate events are studied by spline function interpolation, linear regression, generalized least squares and trend analysis, and the major conclusions are summarized as follow: All the temperature indices including average temperature, average temperature anomaly, average maximum and minimum temperature annually, in January and July had showed an upward trend, with an asymmetric trend temporally, whereas the upward trend in winter is greater than that annually and in summer. The spatial distribution of inter-annual temperature changes showed that rates of temperature change tend to increase gradually, centered at north of Chengde, but with obvious spatial and seasonal differences. That is to say, at high latitude to north direction; generally temperature rise rate in July is low, while high in January. Annual average air temperature, temperatures in April, July, October and January had showed an upward trend with rates of 0.3785°C/10a, 0.4371°C/10a, 0.1988°C/10a, 0.2682°C/10a and 0.4841°C/10a respectively. Extreme maximum and minimum annual temperatures showed warming trends. And extreme minimum temperature warming trend is much higher than the increase in extreme maximum temperatures, with rates of 0.85 °C/10a, and 0.17 °C/10a. Days with the maximum temperature above 35°C and extreme high temperature days tend to increase, where the former days change was not statistically significant; and days with the minimum temperature below 0°C and extreme minimum days significantly tend to become less, except in Chengde station, which making frost-free period significantly longer, especially in the western region, and frost season shortened by nearly 30 days in the past 50 years in the region.