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NewsCongratulations to Jiang jiang Passing her Ph.D. Dissertations smoothly
[2015-05-18]
Jiang jiang successfully passed through the doctoral dissertation defense on May 8th 2015 at the 303 conference room of the IAP scientific research building. Her doctoral thesis title is the changes in monsoon and drought areas and climate change projection over China.
The vast territory determines the climate differences between regions and seasons for China. The dry-wet distribution in China shows humid in the East and arid in the West. Both the temporal and spatial distributions of rain belt are mainly influenced by the strength, the onset and other factors of East Asia summer monsoon, It affects the drought and flood in East China, which also costs a lot. Considering the differences between dry and wet regions, we focus on the changes of monsoon and arid areas and their modes. Based on the observation, all available CMIP5 (Coupled Model Intercomparison Project Phase 5) models have been used to simulate monsoon and arid area changes in China. Meanwhile, for the climate warming differs in areas, we also research on the signals of climate change in China. The main conclusions are summarized as follows.
1. We employed four observed precipitation datasets, including high-resolution gridded one based on 2416 observation stations across China, to analyze monsoon area, its northwestern boundary, and monsoon precipitation intensity for the period of 1961−2009. The results show that the monsoon area accounts for approximately 60% of the mainland China and generally contracts over the period. Monsoon precipitation exhibits apparently interannual and interdecadal variabilities. The average intensity of monsoon precipitation is 4.46 mm day−1. The region between the eastern and western boundary of the northwestern monsoon area belongs to the typical dry-wet transitional zone. The northwestern boundary advances westward south of 40°N, while it retreats eastward north of 40°N, mainly owing to the changes in thermal contrast, atmospheric circulation, and water vapor flux and its divergence.
2. The capabilities of 46 CMIP5 models for simulating the annual, summer, and winter precipitation climatology over China are first examined using the outputs of these models from historical data for the period 1986−2005. 18 models are then chosen to project the changes of monsoon area, and the monsoon precipitation distribution, and its intensity over China under the RCP4.5 scenario. The results show that the monsoon area, monsoon precipitation, and monsoon precipitation intensity will increase in the 21st century, particularly during 2081−2099. The increase in the monsoon precipitation is mainly derived from the increase in the monsoon area. Both thermal and dynamic conditions will be favorable for increased monsoon precipitation intensity and greater water vapor transport in eastern China, resulting in the expansion of the monsoon area in China.
3. Based on the dry-wet index, we analyzed the changes of arid area and chose better CMIP5 models to project. The results show the dry-wet index decreases for the period of 1962−2011 over China. It tends to be wet in West China and be dry in East China. The humid and extreme arid area significantly reduce, in contrast with the expansion of the semihumid, semiarid and arid area, which prove the enlargement of the climatic sensitive region. The distributions of dry-wet index in spring and autumn are consistent with the annual characteristics, but it also tends to be dry in Northwest in winter and be wet in Southeast in summer. Under RCP4.5 scenario, 18 chosen models show the humid, arid and extreme arid area would decrease in the 21st century. And the semiarid and semihumid area would still increase with high climatic sensitivity. During the different periods in the 21st century, the annual precipitation would decrease in Southeast and the potential evapotranspiration would increase over the whole area, which results in the dry-wet index rise in most area except West China.
4. The abilities of 42 CMIP5 models in simulating the annual and seasonal temperature and precipitation over China are first examined by using their historical experiments for 1986–2005, and then 39 relatively reliable models are chosen to project temperature and precipitation changes against the natural internal variability over the country under the Representative Concentration Pathways (RCP) scenarios in the 21st century. The results show the annual and seasonal warming at the beginning of this century relative to 1986–2005 is larger than the background variability over the whole of the country, even under the lowest emission scenario. For 2081–2099 relative to 1986–2005, the increase of temperature has been already beyond internal variability largely. The large changes with high model agreement for annual precipitation only occur over the northern Tibetan Plateau and Northeast China, which is mainly due to the robust changes in winter and spring under RCP6.0 and RCP8.5.
The vast territory determines the climate differences between regions and seasons for China. The dry-wet distribution in China shows humid in the East and arid in the West. Both the temporal and spatial distributions of rain belt are mainly influenced by the strength, the onset and other factors of East Asia summer monsoon, It affects the drought and flood in East China, which also costs a lot. Considering the differences between dry and wet regions, we focus on the changes of monsoon and arid areas and their modes. Based on the observation, all available CMIP5 (Coupled Model Intercomparison Project Phase 5) models have been used to simulate monsoon and arid area changes in China. Meanwhile, for the climate warming differs in areas, we also research on the signals of climate change in China. The main conclusions are summarized as follows.
1. We employed four observed precipitation datasets, including high-resolution gridded one based on 2416 observation stations across China, to analyze monsoon area, its northwestern boundary, and monsoon precipitation intensity for the period of 1961−2009. The results show that the monsoon area accounts for approximately 60% of the mainland China and generally contracts over the period. Monsoon precipitation exhibits apparently interannual and interdecadal variabilities. The average intensity of monsoon precipitation is 4.46 mm day−1. The region between the eastern and western boundary of the northwestern monsoon area belongs to the typical dry-wet transitional zone. The northwestern boundary advances westward south of 40°N, while it retreats eastward north of 40°N, mainly owing to the changes in thermal contrast, atmospheric circulation, and water vapor flux and its divergence.
2. The capabilities of 46 CMIP5 models for simulating the annual, summer, and winter precipitation climatology over China are first examined using the outputs of these models from historical data for the period 1986−2005. 18 models are then chosen to project the changes of monsoon area, and the monsoon precipitation distribution, and its intensity over China under the RCP4.5 scenario. The results show that the monsoon area, monsoon precipitation, and monsoon precipitation intensity will increase in the 21st century, particularly during 2081−2099. The increase in the monsoon precipitation is mainly derived from the increase in the monsoon area. Both thermal and dynamic conditions will be favorable for increased monsoon precipitation intensity and greater water vapor transport in eastern China, resulting in the expansion of the monsoon area in China.
3. Based on the dry-wet index, we analyzed the changes of arid area and chose better CMIP5 models to project. The results show the dry-wet index decreases for the period of 1962−2011 over China. It tends to be wet in West China and be dry in East China. The humid and extreme arid area significantly reduce, in contrast with the expansion of the semihumid, semiarid and arid area, which prove the enlargement of the climatic sensitive region. The distributions of dry-wet index in spring and autumn are consistent with the annual characteristics, but it also tends to be dry in Northwest in winter and be wet in Southeast in summer. Under RCP4.5 scenario, 18 chosen models show the humid, arid and extreme arid area would decrease in the 21st century. And the semiarid and semihumid area would still increase with high climatic sensitivity. During the different periods in the 21st century, the annual precipitation would decrease in Southeast and the potential evapotranspiration would increase over the whole area, which results in the dry-wet index rise in most area except West China.
4. The abilities of 42 CMIP5 models in simulating the annual and seasonal temperature and precipitation over China are first examined by using their historical experiments for 1986–2005, and then 39 relatively reliable models are chosen to project temperature and precipitation changes against the natural internal variability over the country under the Representative Concentration Pathways (RCP) scenarios in the 21st century. The results show the annual and seasonal warming at the beginning of this century relative to 1986–2005 is larger than the background variability over the whole of the country, even under the lowest emission scenario. For 2081–2099 relative to 1986–2005, the increase of temperature has been already beyond internal variability largely. The large changes with high model agreement for annual precipitation only occur over the northern Tibetan Plateau and Northeast China, which is mainly due to the robust changes in winter and spring under RCP6.0 and RCP8.5.
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