Climate change and variability using European Centre for Medium-Range Weather Forecasts reanalysis (ERA-40) temperatures on the Tibetan Plateau

[1] Surface air temperature measurements from meteorological stations on the Tibetan Plateau are compared to 2-m temperatures from the European Centre for MediumRange Weather Forecasts (ECMWF) reanalysis (ERA-40) to assess the accuracy of this reanalysis product. We focus on ERA-40 grid cells containing at least four stations. The reanalysis temperatures are consistently lower, by as much as 7 C. However, temporal correlations are high, indicating that ERA-40 captures the interannual variability very well. The temperature bias is almost exclusively due to differences between the grid cell and the station elevations. We conclude that the ERA-40 temperatures provide better spatial fields of temperature than is possible with stations in this topographically complex, data-sparse area. Using this spatially and temporally continuous data set, we provide a temperature climatology and assess longterm climate trends. The high elevations of the western plateau are generally 10 C cooler than the eastern plateau. During winter, 2-m temperatures are below 0 C on the entire plateau, with summer values of only 0 C in the west and 10 C in the east. While station records point to a long-term climate warming trend, no trends are observed in ERA-40. This could be due to inadequacies of the reanalysis data, although we see no evidence of anomalous nonclimatic shifts. The significant trends in station data may reflect the extensive land use change and industrialization that has occurred on the Tibetan Plateau. Reanalysis data are less influenced by these local effects.