Evaluation of climate on the Tibetan Plateau using ERA-Interim reanalysis and gridded observations during the period 1979-2012

The Tibetan Plateau (TP) is a vast elevated plateau in central Asia, and profoundly impacts regional weather and climate, and even global atmospheric circulation. Here, two frequently used ERA-Interim reanalyses with a spatial resolution of 1.5° × 1.5° (EIN15) and 0.75° × 0.75° (EIN75) are evaluated using a gridded observation dataset at 0.25° spatial resolution from the National Climate Center in China across the TP that covers the period 1979-2012. Climatological characteristics, mean monthly changes, and spatial-temporal trends are examined, with a focus on air temperature and precipitation. Topographic corrections for temperature in ERA-Interim are first conducted based on a vertical temperature lapse rate. The results show that EIN15 and EIN75 with topographic correction closely reproduce the spatial distribution and mean monthly change of temperature on the TP, notwithstanding some cold biases not seen in the observations. The two reanalysis datasets exhibit significant temperature increases over most of the TP, which is similar to the observations. However, the trends exhibit different spatial patterns for all seasons aside from summer, and have lower magnitudes than the observations. EIN15 and EIN75 also reproduce the broad spatial distribution of precipitation, but overestimate precipitation amounts, especially on the southern TP. They also capture some of the observed spatial patterns in the precipitation trend for the period 1979-2012, particularly in winter. Overall, the mean monthly change, mean annual, winter, and summer climatology, and their temporal trends of temperature reproduced by the ERA-Interim data are much better than those of precipitation. As a result of its higher resolution and more accurate topography, EIN75 generates a closer fit to the observed temperatures on the TP than EIN15, but there are no significant differences in precipitation between the two reanalysis datasets. Evaluation of these datasets would be very informative for further climate research and simulations on the TP.