Under the background of climate change, extreme weather events (e.g., heavy rainfall, heat wave, and cold damage) in China have been occurring more frequently with an increasing trend of induced meteorological disasters. Therefore, it is of great importance to carry out research on forecasting of extreme weather. This paper systematically reviewed the primary methodology of extreme weather forecast, current status in development of ensemble weather forecasting based on numerical models and their applications to forecast of extreme weather, as well as progress in approaches for correcting ensemble probabilistic forecast. Nowadays, the forecasting of extreme weather has been generally dominated by methodology using dynamical models. That is to say, the dynamical forecasting methods based on ensemble probabilistic forecast information have become prevailing in current operational extreme weather forecast worldwide. It can be clearly found that the current major directions of research and development in this field are the application of ensemble forecasts based on numerical models to forecasting of extreme weather, and its improvement through bias correction of ensemble probabilistic forecast. Based on a relatively comprehensive review in this paper, some suggestions with respect to development of extreme weather forecast in future were further given in terms of the issues of how to propose effective approaches on improving level of identification and forecasting of extreme events.
The possible changes of extreme climates over China under 1.5 ℃ global warming scenario were investigated by using the output of CORDEX (COordinated Regional Downscaling Experiment) experiments with a regional air-sea coupled model FROALS over East Asia domain. Results indicated that compared to the baseline period of 1986-2005, warm events would significantly increase while cold events would significantly decrease over China in a 1.5 ℃ warmer world. The risks of extreme and moderate warm events would be 2.14 and 1.93 times of that in the baseline period, respectively. The risks of extreme and moderate cold events would be 0.58 and 0.63 times of that in the baseline period, respectively. Compared to other sub-regions, the increasing amplitude of extreme warm events would be higher in North China, while the decreasing amplitude of extreme cold events would be higher in Northeast China. Risks of extreme dry events would increase in Northwest China, Tibetan Plateau and Northeast China (1.13, 1.02 and 1.22 times of that in baseline period). Precipitation intensity and extreme wet events would increase significantly over most parts of China, and the increasing amplitudes extreme wet events will be higher in North China and South China (1.88 and 1.85 times of that in the baseline period). Days when people may feel uncomfortable would increase significantly in eastern China, and compared to simple extreme warm events, the increasing amplitude of extreme uncomfortable days would be larger. The absolute changes of heating degree-days would be larger than that of cooling degree-days (-258℃·d and 72℃·d, respectively) in eastern China, but the relative change of heating degree-days would be smaller than cooling degree-days (-10% and 82%, respectively).
Large-scale, low frequency modes such as the North Atlantic Oscillation(NAO)and blocking, have an important modulation on the northern hemisphere weather and climate. In this paper, the physical mechanism studies on inter-decadal and decadal variability of NAO and blocking were summarized. The relationship between NAO regime transitions and the interannual variability of NAO in winter during was examined by using a statistical approach. The time-space relationship between NAO and European blocking were discussed. Based on two extreme cold and snowstorm events, the impacts on local weather especially the extreme events within the life cycle (two weeks) of the NAO and blocking were further examined. It was found that the frequently occurrence of the Eurasian extreme snowstorm was closely related to the special combination of NAO and blocking regime. In addition, the development of theoretical modes for NAO and blocking was discussed and issues that remain to be solved were proposed.
With the risk of global warming, exploring the changing pattern of extreme climate events in different places is explored for disaster prevention and mitigation. The 0.5°×0.5° grid dataset of daily temperature and precipitation from China Meteorological Administration was used to defined extreme climate events based on the 16 kinds of extreme temperature and precipitation indices. Spatio-temperal variations of the extreme temperature and precipitation events were analyzed through the modified MannKendall trend detecting method across the Pearl River basin, and the significance and consistency of the observed trends were also assessed in a regional perspective. Additionally, whether the observed trends are significantly linked to the largescale climate fluctuation system was investigated. The results indicate that a trend of more extreme high temperature events and less extreme low temperature events, more short time precipitation events and less long time precipitation events has been found in the Pearl River basin over the past half century, which could, consequently, increase the drought and flood risks. It is worthwhile to note that the trends of extreme temperature events are field significant and regional consistent, while the trends of extreme precipitation events are not. Since no significant covariability has been found between the observed trends and the large-scale climate fluctuation system characterized by the multivariate ENSO index, these trends can not be seen as the inevitable outcome of largescale climate fluctuation. Instead, that may be attributed to the common effects of natural and anthropogenic climate change.
Studies on extreme precipitation events during last 50 years indicated that the frequency and intensity of precipitation extremes increased but exhibited distinct regional difference under the background of global warming. Observations showed that extreme precipitation increased in mid-lower reaches of the Yangtze River, southeast and some regions in northwestern China, moreover the decreasing trends of extreme precipitation were investigated in north, northeast and southwest regions. Overall prediction of models suggested that the extreme precipitation in China would be polarized although differences of outputs presented between different models. Concepts and definitions of extreme precipitation events were investigated by analyzing the relationship between mean and extreme from the angle of statistics, and then the trends of precipitation extremes were analyzed in different regions. Physical mechanisms and processes affecting extreme precipitation were summarized from the viewpoint of air-sea interaction taking Yangtze River basin, where the trends of extreme precipitation were complex, as typical climate zone, on the basis of summary of studies of extreme precipitation in China. However, the definitions that can reflect the essence of extreme precipitation need further study, and the physical processes affecting extreme precipitation are not fully understood. In addition, the new impact factors are constantly discovered along with the in-depth study of extreme precipitation events.
Because of the ever-increasing global warming，the frequency of extreme rainfall and regional group slope failure events following the heavy rains in mountainous vegetated areas are getting higher and higher. An in-depth research of this problem is not only of great practical significance to landslide susceptibility assessment, but also of an extensive multidisciplinary theoretical value. The existing research achievements in relative fields mainly focused on the interrelation between rainfall events and landslide events, which are no genetic correlation, as well as the aspect of water-rock interaction in slope rockmass and soilmass。But the basic link of rainfall-landslide process chain — the transformation of rainfall into groundwater has received much less attention whether in permeable medium or in the penetration process. The response of groundwater in natural slopes to heavy rainfall is a complicated hydrologic-hydrogeologic process, which involves plants, animals and their life activities. The existing research accumulation in relevant fields provides realistic basis and certain theory reserves for investigating this problem, but it can not cover the kernel mechanism of the process yet. Probing "The response of the groundwater in vegetated slopes in mountainous catchments to heavy rain events" could provide slope hazard warning and prediction with a more clearly theoretical support, and it is also important for deepening the theory of landslides caused by groundwater.
This paper introduces the overall objectives, major contents, and some preliminary results of the 973 project “Variability of the water and energy cycles and their impact on the extreme climate over China under the global warming background”. The major results contain the field experiments on the land air exchange of water and energy performed in Dunhuang and Linze stations, the analysis of the variability of frequency and intensity of extreme climates in China both in the observation and the climate models, detections on the new approaches of seasonal climate prediction. The paper also provides the future plans of this 973 project in the future years.
More and more researches pay attention to extreme events because of their destructive impacts. Both observing and modeling studies found that extreme temperature and precipitation had significant changes. Further more, there may be more severe extreme events in the future with global warming. Of course, there are still many uncertainties contained in these results. Two main factors contribute to these uncertaintiesne. One is associated with models. There are usually great difference of outputs between different models; the other is the possible difference resulted from the period of different length analyzed. From the definition of extreme events, progresses about the study of extreme events in the last few years are described in detail first for both observing and modeling studies. Then the main progresses are listed, and some problems hanging in doubt are summarized.
Predictions for modern global warming resulting from increased CO2 levels have caused a heightened interest in the mechanics of ancient warm climates and especially of geologically abrupt warming events. Certain key intervals of the Cretaceous and Paleogene marked by rapid climate change are significant to current Earth science objectives because focused research has the potential to considerably improve our understanding of the general dynamics of the Earth during rapid perturbation of carbon cycle. These intervals mainly include: the Paleocene-Eocene Thermal Maximum (PETM, ~55 Ma) and Oceanic Anoxic Events (OAEs) in the late early Aptian (OAE1a，Selli Level, ~120 Ma) and at the Cenomanian-Turonian Boundary (OAE2, Bonarelli Level, ~93.5 Ma). Known as one of the most extreme and abrupt warming episodes since the mid-Cretaceous, the PETM is characterized by a rapid ~5℃ increase in deep ocean, about 4 to 8℃ increase in surface ocean, and a prominent negative carbon isotope excursion of at least 3.0‰ in less than 10 ka. One plausible explanation for the observed PETM δ13C excursion involves massive release of CH4 from gas hydrates in the ocean. The OAEs represent major perturbations of the ocean system defined by massive deposition of organic matter in marine environments. Integrated Ocean Drilling Program (IODP) includes the extreme climates as one of major scientific objectives. World-wide oceans with the minimal diagenesis in Cretaceous and Cenozoic sediments will be drilled by special drilling strategies to yield critical information of our understanding of these climatic extremes under a Milankovitch astronomically-calibrated time scale. The end is fundamental to a quantitative description of global change.
