Gao Xuejie

Simulation of Effects of Land Use Change on Climate in China by a Regional Climate Model

Climate effects of land use change in China as simulated by a regional climate model (RegCM2) are investigated. The model is nested in one-way mode within a global coupled atmosphere-ocean model (CSIRO R21L9 AOGCM). Two multi-year simulations, one with current land use and the other with potential vegetation cover, are conducted. Statistically significant changes of precipitation, surface air temperature, and daily maximum and daily minimum temperature are analyzed based on the difference between the two simulations. The simulated effects of land use change over China include a decrease of mean annual precipitation over Northwest China, a region with a prevalence of arid and semi-arid areas; an increase of mean annual surface air temperature over some areas; and a decrease of temperature along coastal areas. Summer mean daily maximum temperature increases in many locations, while winter mean daily minimum temperature decreases in East China and increases in Northwest China. The upper soil moisture decreases significantly across China. The results indicate that the same land use change may cause different climate effects in different regions depending on the surrounding environment and climate characteristics.

Land use effects on climate in China as simulated by a regional climate model

A regional climate model (RegCM3) nested within ERA40 re-analyzed data is used to investigate the climate effects of land use change over China. Two 15-year simulations (1987–2001), one with current land use and the other with potential vegetation cover without human intervention, are conducted for a domain encompassing China. The climate impacts of land use change are assessed from the difference between the two simulations. Results show that the current land use (modified by anthropogenic activities) influences local climate as simulated by the model through the reinforcement of the monsoon circulation in both the winter and summer seasons and through changes of the surface energy budget. In winter, land use change leads to reduced precipitation and decreased surface air temperature south of the Yangtze River, and increased precipitation north of the Yangtze River. Land use change significantly affects summer climate in southern China, yielding increased precipitation over the region, decreased temperature along the Yangtze River and increased temperature in the South China area (south-end of China). In summer, a reduction of precipitation over northern China and a temperature rise over Northwest China are also simulated. Both daily maximum and minimum temperatures are affected in the simulations. In general, the current land use in China leads to enhanced mean annual precipitation and decreased annual temperature over south China along with decreased precipitation over North China.

Climate Change over China in the 21st Century as Simulated by BCC_CSM1.1-RegCM4.0

Abstract Driven by the global model, Beijing Climate Center Climate System Model version 1.1 (BCC_ CSM1.1), climate change over China in the 21st century is simulated by a regional climate model (RegCM4.0) under the new emission scenarios of the Representative Concentration Pathways—RCP4.5 and RCP8.5. This is based on a period of transient simulations from 1950 to 2099, with a grid spacing of 50 km. The present paper focuses on the annual mean temperature and precipitation in China over this period, with emphasis on their future changes. Validation of model performance reveals marked improvement of the RegCM4.0 model in reproducing present day temperature and precipitation relative to the driving BCC_CSM1.1 model. Significant warming is simulated by both BCC_CSM1.1 and RegCM4.0, however, spatial distribution and magnitude differ between the simulations. The high emission scenario RCP8.5 results in greater warming compared to RCP4.5. The two models project different precipitation changes, characterized by a general increase in the BCC_CSM1.1, and broader areas with decrease in the RegCM4.0 simulations.

Simulation and Projection of Monso on Rainfall and Rain Patterns over Eastern China under Global Warming by RegCM3

Abstract The authors investigate possible changes of monsoon rainfall and associated seasonal (June-July-August) anomaly patterns over eastern China in the late 21st century under the Intergovernmental Panel on Climate Change (IPCC) Special Report on Emission Scenarios (SRES) A2 emission scenario as simulated by a high-resolution regional climate model (RegCM3) nested in a general circulation model (FvGCM/CCM3). Two sets of multi-decadal simulations are performed at 20-km grid spacing for present day and future climate conditions. Results show that the RegCM3 reproduces the mean rain-fall distribution; however the evolution of the monsoon rain belt from South China to North China is not well simulated. Concerning the rain pattern classifications, RegCM3 overestimates the occurrence of Pattern 1 (excessive rainfall in northern China) and underestimates that of Pattern 2 (increased rainfall over the Huai River basin). Under future climate conditions, RegCM3 projects less occurrence of Pattern 1, more of Pattern 2, and little change of Pattern 3 (rainfall increase along the Yangtze River). These results indicate that there might be increased rainfall over the Huai-Yellow River area and reduced rainfall over North China in the future, while rain-fall over the lower reaches of the Yangtze River basin is not modified significantly. Uncertainties exist in the present study are also discussed.

Regional Climate Change and Uncertainty Analysis based on Four Regional Climate Model Simulations over China

Abstract Four sets of climate change simulations at grid spacing of 50 km were conducted over East Asia with two regional climate models driven at the lateral boundaries by two global models for the period 1981–2050. The focus of the study was on the ensemble projection of climate change in the mid-21st century (2031–50) over China. Validation of each simulation and the ensemble average showed good performances of the models overall, as well as advantages of the ensemble in reproducing present day (1981–2000) December–February (DJF), June–August (JJA), and annual (ANN) mean temperature and precipitation. Significant warming was projected for the mid-21st century, with larger values of temperature increase found in the northern part of China and in the cold seasons. The ensemble average changes of precipitation in DJF, JJA, and ANN were determined, and the uncertainties of the projected changes analyzed based on the consistencies of the simulations. It was concluded that the largest uncertainties in precipitation projection are in eastern China during the summer season (monsoon precipitation).

The Effects of Land Cover Change on Regional Climate over the Eastern Part of Northwest China

Abstract A regional climate model (RegCM4) is employed to investigate the impacts of land use/cover change (LUCC) on the climate over the eastern part of Northwest China (ENW) in the periods of 2001 and 2011. The results indicated that the LUCC in ENW, which was characterized by desert retreat, reforestation, and farmland expansion, led to significant local changes in surface air temperature (within ∼0.3C) and slight regional changes in precipitation (within ∼15%) in summer. In the desert retreat area, the net absorbed shortwave radiation had a greater influence than evaporative cooling, leading to increases in the daily mean and maximum temperature. Besides, the daily mean and maximum temperatures increased in the reforestation area but decreased in the farmland expansion area. As surface albedo showed no significant change in these regions, the temperature increase in the reforestation area can be attributed to a decrease in evaporation, while the opposite effect appears to have been the case in the farmland expansion area.