Developing a temporally accurate air temperature dataset for Mainland China

Spatially continuous satellite data have been widely used to estimate monthly air temperature (Ta). However, it is still not clear whether the estimated monthly Ta is temporally consistent with observed Ta or not. In this study, the accuracies of interannual variations and temporal trends in estimated monthly Ta were systematically analyzed for Mainland China during 2001-2018. The differences in accuracy among five ways to input data into the model were investigated. The Cubist algorithm and ten variables were used to estimate monthly Ta. It was found that inputting data for the same month into the model can generate more accurate results than inputting all data into the model. Using temporal variables (i.e., month and year) can significantly increase the accuracy of estimated Ta. These results can be explained by different relationships between Ta and auxiliary variables that appear at different times. Thus, using temporal variables can help distinguish between different relationships and improve accuracy levels of the estimated Ta. When applying the best method (inputting data for the same month into the model and using the year as a temporal variable), the coefficient of determination (R²) of estimated monthly mean Ta, interannual variations in monthly mean Ta and temporal trends in monthly mean Ta were recorded as 0.997, 0.731 and 0.848, respectively. The root mean squared errors (RMSEs) of estimated monthly mean Ta, interannual variations in monthly mean Ta and temporal trends in monthly mean Ta were recorded as 0.629 °C, 0.593 °C and 0.201 °C/decade, respectively. An accurate, national coverage, 1 km spatial resolution and long time series (2001-2018) monthly mean, maximum and minimum Ta dataset was finally developed. The dataset can be of great use to many fields such as climatology, hydrology and ecology.