Development and properties of 0.25-degree gridded evapotranspiration data fields of China for hydrological studies

Construction and spatial and temporal properties for a 0.25° resolution gridded data set of monthly Penman–Monteith reference evapotranspiration estimates over the territory of the PR China (including Tibet) and adjacent areas (15°N–55°N, 65°E–135°E) for the period 1951–1990 are described. To account for the interaction between climate and the rugged topography of the study area the REGEOTOP procedure was used to incorporate the effects of relief forms into the interpolation. Evapotranspiration rates over much of China show a range of values (annual rates from 550–2300 mm) and variability comparable to precipitation. Monthly evapotranspiration rates are distributed more evenly over the year than precipitation, are out of phase with the summer precipitation peak and in some cases may reach winter rates comparable to those in summer. Hydrological studies based on idealized regular seasonal variation of evapotranspiration may contain considerable errors due to inherent seasonal fluctuations as compared to precipitation. High resolution gridded PET data that account for the influence of topography on climate are required to resolve the spatial heterogeneity of topography and land use in order to allow precise estimates of actual evapotranspiration and run-off. The spatial distribution of runoff appears to have remained fairly constant over most of China during 1951–1990 which stands in contrast to the anticipated increase in hydrological activity under global warming conditions.