Xuejie Gao

Regional Climate Modeling for the Developing World: The ICTP RegCM3 and RegCNET

Regional climate models are important research tools available to scientists around the world, including in economically developing nations (EDNs). The Earth Systems Physics (ESP) group of the Abdus Salam International Centre for Theoretical Physics (ICTP) maintains and distributes a state-of-the-science regional climate model called the ICTP Regional Climate Model version 3 (RegCM3), which is currently being used by a large research community for a diverse range of climate-related studies. The RegCM3 is the central, but not only, tool of the ICTP-maintained Regional Climate Research Network (RegCNET) aimed at creating south–south and north–south scientific interactions on the topic of climate and associated impacts research and modeling. In this paper, RegCNET, RegCM3, and illustrative results from RegCM3 benchmark simulations applied over south Asia, Africa, and South America are presented. It is shown that RegCM3 performs reasonably well over these regions and is therefore useful for climate studies in...

Heat stress intensification in the Mediterranean climate change hotspot

[1] We find that elevated greenhouse gas concentrations dramatically increase heat stress risk in the Mediterranean region, with the occurrence of hot extremes increasing by 200 to 500% throughout the region. This heat stress intensification is due to preferential warming of the hot tail of the daily temperature distribution, with 95th percentile maximum and minimum temperature magnitude increasing more than 75th percentile magnitude. This preferential warming of the hot tail is dictated in large part by a surface moisture feedback, with areas of greatest warm-season drying showing the greatest increases in hot temperature extremes. Fine-scale topographic and humidity effects help to further dictate the spatial variability of the heat stress response, with increases in dangerous Heat Index magnified in coastal areas. Further, emissions deceleration substantially mitigates heat stress intensification throughout the Mediterranean region, implying that emissions reductions could reduce the risk of increased heat stress in the coming decades. Citation: Diffenbaugh, N. S., J. S. Pal, F. Giorgi, and X. Gao (2007), Heat stress intensification in the Mediterranean climate change hotspot, Geophys. Res. Lett., 34, L11706, doi:10.1029/2007GL030000.

Higher Hydroclimatic Intensity with Global Warming

AbstractBecause of their dependence on water, natural and human systems are highly sensitive to changes in the hydrologic cycle. The authors introduce a new measure of hydroclimatic intensity (HY-INT), which integrates metrics of precipitation intensity and dry spell length, viewing the response of these two metrics to global warming as deeply interconnected. Using a suite of global and regional climate model experiments, it is found that increasing HY-INT is a consistent and ubiquitous signature of twenty-first-century, greenhouse gas–induced global warming. Depending on the region, the increase in HY-INT is due to an increase in precipitation intensity, dry spell length, or both. Late twentieth-century observations also exhibit dominant positive HY-INT trends, providing a hydroclimatic signature of late twentieth-century warming. The authors find that increasing HY-INT is physically consistent with the response of both precipitation intensity and dry spell length to global warming. Precipitation intensi...

Comparison of convective parameterizations in RegCM4 experiments over China with CLM as the land surface model

Abstract In the latest version of the International Centre for Theoretical Physics’ regional climate model, RegCM4, CLM was introduced as a new land surface scheme. The performance over China of RegCM4-CLM with different convection schemes is analyzed in this study, based on a series of short-term experiments. The model is driven by ERA-Interim data at a grid spacing of 25 km. The convection schemes employed are: Emanuel; Grell; Emanuel over land and Grell over ocean; Grell over land and Emanuel over ocean; and Tiedtke. The simulated mean surface air temperature and precipitation in December–February–January and June–July–August are compared against observation. In general, better performance of Emanuel is found both for temperature and precipitation, and in both seasons. Thus, the model physics of CLM and Emanuel for the land surface processes and convection, respectively, are recommended for further application of RegCM4 over the China region. The deficiencies that remain in the model are also outlined and discussed.

Multimodel ensemble projection of precipitation in eastern China under A1B emission scenario

As part of the Regional Climate Model Intercomparison Project for Asia, future precipitation projection in China is constructed using five regional climate models (RCMs) driven by the same global climate model (GCM) of European Centre/Hamburg version 5. The simulations cover both the control climate (1978–2000) and future projection (2041–2070) under the Intergovernmental Panel on Climate Change emission scenario A1B. For the control climate, the RCMs have an advantage over the driving GCM in reproducing the summer mean precipitation distribution and the annual cycle. The biases in simulating summer precipitation mainly are caused by the deficiencies in reproducing the low-level circulation, such as the western Pacific subtropical high. In addition, large inter-RCM differences exist in the summer precipitation simulations. For the future climate, consistent and inconsistent changes in precipitation between the driving GCM and the nested RCMs are observed. Similar changes in summer precipitation are projected by RCMs over western China, but model behaviors are quite different over eastern China, which is dominated by the Asian monsoon system. The inter-RCM difference of rainfall changes is more pronounced in spring over eastern China. North China and the southern part of South China are very likely to experience less summer rainfall in multi-RCM mean (MRM) projection, while limited credibility in increased summer rainfall MRM projection over the lower reaches of the Yangtze River Basin. The inter-RCM variability is the main contributor to the total uncertainty for the lower reaches of the Yangtze River Basin and South China during 2041–2060, while lowest for Northeast China, being less than 40%.

Regional earth system modeling: review and future directions

Abstract The authors review recent advances in the development of coupled Regional Earth System Models (RESMs), a field that is still in its early stages. To date, coupled regional atmosphere-ocean-sea ice, atmosphere-aerosol and atmosphere-biosphere models have been developed, but they have been applied only to limited regional settings. Much more work is thus needed to assess their transferability to a wide range of settings. Future challenges in regional climate modeling are identified, including the development of fully coupled RESMs encompassing not only atmosphere, ocean, cryosphere, biosphere, chemosphere, but also the human component in a fully interactive way.

Projected Changes in Temperature and Precipitation Extremes over China as Measured by 50-yr Return Values and Periods Based on a CMIP5 Ensemble

Future changes in the 50-yr return level for temperature and precipitation extremes over mainland China are investigated based on a CMIP5 multi-model ensemble for RCP2.6, RCP4.5 and RCP8.5 scenarios. The following indices are analyzed: TXx and TNn (the annual maximum and minimum of daily maximum and minimum surface temperature), RX5day (the annual maximum consecutive 5-day precipitation) and CDD (maximum annual number of consecutive dry days). After first validating the model performance, future changes in the 50-yr return values and return periods for these indices are investigated along with the inter-model spread. Multi-model median changes show an increase in the 50-yr return values of TXx and a decrease for TNn, more specifically, by the end of the 21st century under RCP8.5, the present day 50-yr return period of warm events is reduced to 1.2 yr, while extreme cold events over the country are projected to essentially disappear. A general increase in RX5day 50-yr return values is found in the future. By the end of the 21st century under RCP8.5, events of the present RX5day 50-yr return period are projected to reduce to < 10 yr over most of China. Changes in CDD-50 show a dipole pattern over China, with a decrease in the values and longer return periods in the north, and vice versa in the south. Our study also highlights the need for further improvements in the representation of extreme events in climate models to assess the future risks and engineering design related to large-scale infrastructure in China.摘 要利用CMIP5多个全球气候模式的模拟结果预估了RCP2.6, RCP4.5和RCP8.5温室气体排放情景下不同时期中国地区50年一遇极端温度和降水变化, 包括极端高温(TXx), 极端低温(TNn)最大5日降水量(RX5day)和连续干旱日数(CDD). 首先评估了全球气候模式对中国地区极端温度与降水模拟能力, 在此基础上预估了其变化趋势. 结果表明: 50年一遇TXx的值将增加, TNn的值将减小, 尤其在RCP8.5温室气体高排放情景下, 目前50年一遇的极端高温事件在21世纪末将变为1-2年一遇, 极端冷事件将逐渐消失. 50年一遇的极端降水(RX5day)的量值在未来会增加, 同时目前50年一遇的极端降水事件在21世纪末将变为10年一遇. 极端干旱事件(连续无降雨日数)在中国的北方地区将减少, 而在南方将增加.

Use of the RegCM System over East Asia: Review and Perspectives

Abstract The Abdus Salam International Center for Theoretical Physics (ICTP) RegCM system is one of the most commonly used regional climate models (RCMs) over the East Asia region. In this paper, we present a brief review of the RegCM system and its applications to the East Asia region. The model history and plans for future development are described. Previous and ongoing applications, as well as the advantages and biases found in the model system over the East Asia region, are summarized. The model biases that exist are mainly found in the cold seasons, and are characterized by a warm bias at high latitudes and underestimation of precipitation in the south. These biases are similar to those of most global climate models (GCMs). Finally, future plans on the application and development of the model, and specifically on those within the context of the Coordinated Regional Climate Downscaling Experiment (CORDEX), are introduced. This paper is intended to serve as a reference for future users of the RegCM system within the East Asia region.

Future changes in thermal comfort conditions over China based on multi-RegCM4 simulations

ABSTRACT A set of high resolution (25 km) 21st century climate change projections using the regional climate model RegCM4 driven by four global model simulations were conducted over East Asia under the mid-range RCP4.5 scenario. In the present paper, the authors investigate the change in thermal comfort conditions over china based on an ensemble of the projections, using the index of effective temperature (ET), which considers the aggregate effects of temperature, relative humidity, and wind on human thermal perception. The analysis also accounts for exposure as measured by distributed population amount scenarios. The authors find that the general increase in ET leads to a large increase in population exposure to very hot days (a China-aggregated six-fold increase in ‘person-days’ by the end of the 21st century. There is a decrease in cool, cold, and very cold person-days. Meanwhile, a decrease in comfortable day conditions by 22% person-days is found despite an increase in climate-based comfortable days. Analysis of the different contributions to the changes (climate, population, and interactions between the two) show that climate effects play a more important role in the hot end of the thermal comfort categories, while the population effects tend to be dominant in the cold categories. Thus, overall, even a mid-level warming scenario is found to increase the thermal stress over China, although there is a strong geographical dependence. The inclusion of population exposure strongly modulates the climate-only signal, which highlights the need for including socioeconomic factors in the assessment of risks associated with climate change. Graphical Abstract

Effects of climate and potential policy changes on heating degree days in current heating areas of China

Based on climate simulations over East Asia from a high-resolution regional climate model under RCP4.5 and 8.5 scenarios, we examine the impact of future climate change and heating policy changes on energy demand in current central heating areas over China using the heating degree days (HDD) and the number of the heating days (NHD) with different base temperature as the indices. Based on current heating policy in China, significant decreases of NHDs are projected, with larger decreases under RCP8.5 than RCP4.5. This decrease of NHDs would cause a northward shift of the decadal heating boundary line, with significant implications for infrastructure planning and development. Changing the heating policy currently in practice to one used in Europe and USA would cause an immediate jump in NHDs and in HDDs; as warming progresses in the future, these effects attenuate with time in an approximately linear trend under the two scenarios. Under RCP8.5, by 2050, the effects of warming climate would dominate over the heating policy change, and heating demand would be lower than the present day HDD and continue to decrease until the end of the century. Energy demand and the number of the heating days during peak winter shows no dependence on heating policy, as the policy-induced increase of energy demand would occur primarily during warmer months of the year. In addition, the indices are further weighted by population, and results show that increases in both HDDs and NHDs can be found in parts of northern China due to the increased population there by the end of the 21st century.