Entao Yu

Will the Tibetan Plateau warming depend on elevation in the future

Elevation-dependent warming, greater warming at higher elevations, tends to accelerate the ablation of solid water reserves on the Tibetan Plateau and is thus expected to affect the sustainable water supply of the plateau. In the context of a global climate that is predicted to continue to warm, whether elevation-dependent warming exists on the Tibetan Plateau in the future and, if so, what its characteristics and mechanisms are, are important issues that have not yet been fully assessed. Using six sets of high-resolution outputs from dynamical downscaling simulations based on regional climate models, we investigated the future situation regarding the elevation dependency of climate warming on the Tibetan Plateau. The simulated air temperature trends from the six simulations are validated using meteorological station observations. The trends from only two simulations are selected for analysis due to their statistically significant correlation with the observations. The warming rate first increases to a peak and then slightly declines along with elevation increasing from 2000m to 5600m. The peak of the warming rate is reached at variable elevations (4400–5200m), which depends on the intensity of the warming. The elevation at which this peak occurs increases when the warming intensifies. Such elevation-dependent warming is mostly caused by the decrease in upward short-wave radiation due to the depletion of snow based on surface energy budget analysis. These results provide some understanding of the future elevation-dependent warming on the Tibetan Plateau, which will be useful for evaluating the sustainability of water resources of the Tibetan Plateau water-affected area.

Simulation and Projection of Changes in Rainy Season Precipitation over China Using the WRF Model

The Weather Research and Forecasting (WRF) model is used in a regional climate model configuration to simulate past precipitation climate of China during the rainy season (May-September) of 1981–2000, and to investigate potential future (2041–2060 and 2081–2100) changes in precipitation over China relative to the reference period 1981–2000. WRF is run with initial conditions from a coupled general circulation model, i.e., the high-resolution version of MIROC (Model for Interdisciplinary Research on Climate). WRF reproduces the observed distribution of rainy season precipitation in 1981–2000 and its interannual variations better than MIROC. MIROC projects increases in rainy season precipitation over most parts of China and decreases of more than 25 mm over parts of Taiwan and central Tibet by the mid-21st century. WRF projects decreases in rainfall over southern Tibetan Plateau, Southwest China, and northwestern part of Northeast China, and increases in rainfall by more than 100 mm along the southeastern margin of the Tibetan Plateau and over the lower reaches of the Yangtze River during 2041–2060. MIROC projects further increases in rainfall over most of China by the end of the 21st century, although simulated rainfall decreases by more than 25 mm over parts of Taiwan, Guangxi, Guizhou, and central Tibet. WRF projects increased rainfall of more than 100 mm along the southeastern margin of the Tibetan Plateau and over the lower reaches of the Yangtze River and decreased rainfall over Southwest China, and southern Tibetan Plateau by the end of the 21st century.

A simulation study of a heavy rainfall process over the Yangtze River valley using the two-way nesting approach

In this study, the major features of a heavy rainfall event in the Yangtze River region on 3–7 June 2011 and its event-related large-scale circulation and predictability were studied. Both observational analysis and model simulation were used, the latter being based on the Weather Research and Forecasting (WRF) model forced by NCEP Global Forecast System (GFS) datasets. It was found that, during 3–5 June, the western Pacific subtropical high apparently extended to the west and was much stronger, and the Indian summer monsoon trough was slightly weaker than in normal years. The east-west oriented shear line over the middle and lower reaches of the Yangtze River was favorable for the transportation and convergence of water vapor, and the precipitation band was located slightly to the south of the shear line. During 6–7 June, the western Pacific subtropical high retreated eastward, while the trough over the Okhotsk Sea deepened. The low vortex in Northeast China intensified, bringing much more cold air to the middle and lower reaches of the Yangtze River, and the shear line over this area moved slightly southward. The convection band moved southward and became weaker, so the rainfall during 6–7 June weakened and was located slightly to the south of the previous precipitation band. Many of the observed features, including background circulation and the distribution and amount of precipitation, were reproduced reasonably by the WRF, suggesting a feasibility of this model for forecasting extreme weather events in the Yangtze River region.

Precipitation pattern of the mid-Holocene simulated by a high-resolution regional climate model

Early proxy-based studies suggested that there potentially occurred a “southern drought/northern flood” (SDNF) over East China in the mid-Holocene (from roughly 7000 to 5000 years before present). In this study, we used both global and regional atmospheric circulation models to demonstrate that the SDNF—namely, the precipitation increases over North China and decreases over the the lower reaches of the Yangtze River Valley—could have taken place in the mid-Holocene. We found that the SDNF in the mid-Holocene was likely caused by the lower SST in the Pacific. The lowered SST and the higher air temperature over mainland China increased the land-sea thermal contrast and, as a result, strengthened the East Asian summer monsoon and enhanced the precipitation over North China.

Future precipitation changes over China under 1.5 °C and 2.0 °C global warming targets by using CORDEX regional climate models

This study aims to characterize future changes in precipitation extremes over China based on regional climate models (RCMs) participating in the Coordinated Regional Climate Downscaling Experiment (CORDEX)-East Asia project. The results of five RCMs involved in CORDEX-East Asia project that driven by HadGEM2-AO are compared with the simulation of CMA-RegCM driven by BCC-CSM1.1. Eleven precipitation extreme indices that developed by the Expert Team on Climate Change Detection and Indices are employed to evaluate precipitation extreme changes over China. Generally, RCMs can reproduce their spatiotemporal characteristics over China in comparison with observations. For future climate projections, RCMs indicate that both the occurrence and intensity of precipitation extremes in most regions of China will increase when the global temperature increases by 1.5/2.0 °C. The yearly maximum five-day precipitation (RX5D) averaged over China is reported to increase by 4.4% via the CMA-RegCM under the 1.5 °C warming in comparison with the baseline period (1986-2005); however, a relatively large increase of 11.1% is reported by the multi-model ensemble median (MME) when using the other five models. Furthermore, the reoccurring risks of precipitation extremes over most regions of China will further increase due to the additional 0.5 °C warming. For example, RX5D will further increase by approximately 8.9% over NWC, 3.8% over NC, 2.3% over SC, and approximately 1.0% over China. Extremes, such as the historical 20-year return period event of yearly maximum one-day precipitation (RX1D) and RX5D, will become more frequent, with occurrences happening once every 8.8 years (RX1D) and 11.5 years (RX5D) under the 1.5 °C warming target, and there will be two fewer years due to the additional 0.5 °C warming. In addition, the intensity of these events will increase by approximately 9.2% (8.5%) under the 1.5 °C warming target and 12.6% (11.0%) under the 2.0 °C warming target for RX1D (RX5D).