Analysis of sampling error uncertainties and trends in maximum and minimum temperatures in China

In this paper we report an analysis of sampling error uncertainties in mean maximum and minimum temperatures (Tmax and Tmin) carried out on monthly, seasonal and annual scales, including an examination of homogenized and original data collected at 731 meteorological stations across China for the period 1951–2004. Uncertainties of the gridded data and national average, linear trends and their uncertainties, as well as the homogenization effect on uncertainties are assessed. It is shown that the sampling error variances of homogenized Tmax and Tmin, which are larger in winter than in summer, have a marked northwest-southeast gradient distribution, while the sampling error variances of the original data are found to be larger and irregular. Tmax and Tmin increase in all months of the year in the study period 1951–2004, with the largest warming and uncertainties being 0.400°C (10 yr)−1 ± 0.269°C (10 yr)−1 and 0.578°C (10 yr)−1 ± 0.211°C (10 yr)−1 in February, and the least being 0.022°C (10 yr)−1 ± 0.085°C (10 yr)−1 and 0.104°C (10 yr)−1 ±0.070°C (10 yr)−1 in August. Homogenization can remove large uncertainties in the original records resulting from various non-natural changes in China.