Reconstruction of cropland cover is crucial for assessing human impact on the environment. In this study, based on existing studies concerning historical cropland, population data and government inventories, we obtained a provincial cropland area dataset of China for 1661–1996 via collection, revision and reconstruction. Then, the provincial cropland area was allocated into grid cells of 10 × 10 km depending on the land suitability for cultivation. Our reconstruction indicates that cropland increased from ~55.5 × 10⁴ km² in 1661 to ~130.0 × 10⁴ km² in 1996. From 1661 to 1873, cropland expanded tremendously in the Sichuan Basin, and land reclamation was greatly enhanced in North China Plain. For 1873–1980, agricultural development occurred primarily in northeastern China. After 1980, most provinces in the traditionally cultivated region of China experienced decreases in cropland area. In comparison with satellite-based data for 2000, we found that our reconstruction generally captures the spatial distribution of cropland. Also, differences are mostly <20 % (−20 to 20 %). Compared with HYDE 3.1 dataset, which is designed for the global scale, our model is more suitable for reconstructing the historical crop cover of China at 10 × 10 km grid scale. Our reconstruction can be used in climate models to study the impact of crop cover change on the climate and carbon cycle.

The local/regional temperature changes were significantly regulated by land surface changes. This study aims to reveal the effects of vegetation increase/decrease on temperature changes from 1982 to 2000 across the Eastern China. To reach this goal, we performed two 20‐year simulations, dynamical vegetation experiment (DYCV) and fixed vegetation experiment (FIXV), with the coupled Weather Research and Forecast (WRF)‐Noah model. The DYCV used the essential satellite‐measured vegetation variations from 1982 to 2000 while FIXV kept the vegetation properties in 1982 for the entire simulation. The results show that vegetation increase/decrease exerted negative effects locally and the effects were stronger in growth season than that in non‐growth season. From 1982 to 2000, in the areas where vegetation increased, such as North China Plain for the spring and south part of Northeast China for the summer and autumn, climate warming was slowed; whereas, in the areas where vegetation decreased, such as Yangtze River Delta and Pearl River Delta for the summer, climate warming was enhanced. Such negative effect was resulted from changes in partition of surface net radiation between surface latent heat and sensible heat. Increased vegetation caused more evaportranspiration and thus more latent heat and less sensible heat; it is reverse for the decreased vegetation. In comparing, changes in surface net radiation were too slight to be detected. Noted that, due to flaws of coupled WRF‐Noah model, the results for the summer and winter have some uncertainties and needed to be verified with more studies. Copyright © 2013 Royal Meteorological Society

Evapotranspiration occurs via land‐atmosphere coupling. To understand the impacts of irrigation on local potential evapotranspiration, we carried out a couple of simulations with the Weather Research and Forecast (WRF) model, where an irrigation scheme was incorporated, for the irrigated area in the middle reaches of the Heihe River, Northwest China. By comparing the irrigation simulation (hereafter, the IRRG case) with the simulation excluding irrigation (hereafter, the NATU case), we found that irrigation may lead to a decrease in reference evapotranspiration (ET₀) during the growing season (May to September), which is a metric of potential evapotranspiration, by approximately 1.05 mm d⁻¹, accounting for approximately 19% of NATU ET₀. The ET₀ in the IRRG is closer to the ground measurements than the NATU ET₀, with a root‐mean‐square error of 0.75 mm d⁻¹ in the IRRG and 1.86 mm d⁻¹ in the NATU cases. Meanwhile, irrigation leads to an actual evapotranspiration (ET_a) increase of approximately 2.1 mm d⁻¹ for croplands. Such an asymmetric relationship between ET₀ decrease and ET_a increase was found over the irrigated croplands. The ET₀ decrease was mainly induced by the moistening and cooling effects of irrigation through intensified evapotranspiration and reduced sensible heat. This study highlights the importance of considering land‐atmosphere coupling when assessing the impacts of climatic change on irrigation water requirements.