Urbanization and air quality as major drivers of altered spatiotemporal patterns of heavy rainfall in China

Context Land use/land cover change and other human activities contribute to the changing climate on regional and global scales, including the increasing occurrence of extreme precipitation events, but the relative importance of these anthropogenic factors, as compared to climatic factors, remains unclear. Objectives The main goal of this study was to determine the relative contributions of human-induced and climatic factors to the altered spatiotemporal patterns of heavy rainfall in China during the past several decades. Methods We used daily precipitation data from 659 meteorological stations in China from 1951 to 2010, climatic factors, and anthropogenic data to identify possible causes of the observed spatiotemporal patterns of heavy rainfall in China in the past several decades, and quantify the relative contributions between climatic and human-induced factors.This research was supported by the 973 Project ‘‘National Key Research and Development Program– Global Change and Mitigation Project: Global change risk of population and economic system: mechanisms and assessments’’ under Grant No. 201531480029, Ministry of Science and Technology of China, People’s Republic of China, the National Natural Science Foundation of Innovative Research Group Project ‘‘Earth Surface Process Model and Simulation’’ under Grant No. 41621061

Impacts of upper tropospheric cooling upon the late spring drought in East Asia simulated by a regional climate model

International audienceResponses of late spring (21 April 20 May) rainfall to the upper tropospheric cooling over East Asia are investigated with a regional climate model based on Laboratoire de Météorologie Dynamique Zoom (LMDZ4-RCM). A control experiment is performed with two runs driven by the mean ERA-40 data during 1958 1977 and 1981 2000, respectively. The model reproduces the major decadal-scale circulation changes in late spring over East Asia, including a cooling in the upper troposphere and an anomalous meridional cell. Accordingly, the precipitation decrease is also captured in the southeast of the upper-level cooling region. To quantify the role of the upper-level cooling in the drought mechanism, a sensitivity experiment is further conducted with the cooling imposed in the upper troposphere. It is demonstrated that the upper-level cooling can generate the anomalous meridional cell and consequently the drought to the southeast of the cooling center. Therefore, upper tropospheric cooling should have played a dominant role in the observed late spring drought over Southeast China in recent decades

The Beijing Climate Center atmospheric general circulation model: description and its performance for the present-day climate

International audienceThe Beijing Climate Center atmospheric general circulation model version 2.0.1 (BCC_AGCM2.0.1) is described and its performance in simulating the present-day climate is assessed. BCC_AGCM2.0.1 originates from the community atmospheric model version 3 (CAM3) developed by the National Center for Atmospheric Research (NCAR). The dynamics in BCC_AGCM2.0.1 is, however, substantially different from the Eulerian spectral formulation of the dynamical equations in CAM3, and several new physical parameterizations have replaced the corresponding original ones. The major modification of the model physics in BCC_AGCM2.0.1 includes a new convection scheme, a dry adiabatic adjustment scheme in which potential temperature is conserved, a modified scheme to calculate the sensible heat and moisture fluxes over the open ocean which takes into account the effect of ocean waves on the latent and sensible heat fluxes, and an empirical equation to compute the snow cover fraction. Specially, the new convection scheme in BCC_AGCM2.0.1, which is generated from the Zhang and McFarlane’s scheme but modified, is tested to have significant improvement in tropical maximum but also the subtropical minimum precipitation, and the modified scheme for turbulent fluxes are validated using EPIC2001 in situ observations and show a large improvement than its original scheme in CAM3. BCC_AGCM2.0.1 is forced by observed monthly varying sea surface temperatures and sea ice concentrations during 1949-2000. The model climatology is compiled for the period 1971-2000 and compared with the ERA-40 reanalysis products. The model performance is evaluated in terms of energy budgets, precipitation, sea level pressure, air temperature, geopotential height, and atmospheric circulation, as well as their seasonal variations. Results show that BCC_AGCM2.0.1 reproduces fairly well the present-day climate. The combined effect of the new dynamical core and the updated physical parameterizations in BCC_AGCM2.0.1 leads to an overall improvement, compared to the original CAM3