Temporal And Spatial Distribution Characteristics And Future Estimates Of Extreme Precipitation In China Under The Background Of Climate Change

Extreme precipitation is one of the indicators of extreme weather and climate change. In order to understand this phenomenon of the climate system under global warming, it is important to explore the temporal and spatial characteristics of extreme precipitation and project the future changes. In this study, we first detect the changes of different intensity precipitation over China based on observed dataset. Second, a new method for identifying regional persistent extreme climate events is applied in this study to investigate the characteristics of precipitation events over the eastern monsoon China. In addition, this study evaluates the models of the fifth phase of the Coupled Model Intercomparison Project(CMIP5) in simulating of the historical monsoon precipitation mean and extremes, and assesses the potential future changes in the Middle and Low Yangtze River Basin(MLYRB). The main conclusions are as follows:(1) Based on a recent daily precipitation dataset of 666 climate stations and robust non-parametric trend detection techniques, the changes in the precipitation characteristics for China from 1960 to 2013 are investigated. All precipitation events are divided into four non-overlapping categories: light, moderate, heavy and very heavy based on percentile thresholds. Then establishing the trends for annual total and precipitation of different intensity categories, and examining their regional and seasonal variations. The results show that there is little change in annual total precipitation for entire China, but distinctive regional patterns existed. In general precipitation is increasing in the west and decreasing in east. Precipitation of different intensities in general changes in the same direction as the mean, but heavy and very heavy precipitation events in general have higher rates of change than mean precipitation. The exception is the southeast region, where despite the slight decrease in mean precipitation, heavy and very heavy precipitation still increase significantly.(2) In addition, based on the multiple regression models, the contribution of changes of frequency and intensity to total precipitation change is explored, and the contributions of changes of precipitation at different intensities to total precipitation change. For western China, total precipitation change is associated more with frequency change, whereas in eastern China intensity contributes more. For precipitation amount, moderate, heavy and very heavy precipitation all contribute to the total change, with little contribution from light precipitation change. For frequency, changes in light and moderate precipitation frequency dominate the total change, with very little contributions from heavy and very heavy precipitation frequency change. Moreover, the linkage between summer precipitation in eastern China and the East Asian Summer Monsoon(EASM) is examined, the result shows that the northern decrease and southern increase in summer precipitation was likely caused by the weakening of EASM over the study period.(3) Based on the daily precipitation dataset of 470 climate stations over the eastern monsoon China, an objective identification technique is applied to identify the precipitation event which generally has a certain impacted area and duration. Under the new technique, 2687 precipitation events are identified for the period 1960-2013. All events are classified into four grades: very strong, strong, moderate and weak according to the integrated index. In the last 54 years, there are 269 very strong events, 403 strong events, 672 moderate events and 1343 weak events. The precipitation events mainly occur from May to September and the peak frequency appears in July. Spatially, the events are mainly located in the in the middle and low Yangzi river basin and southeastern China, especially the very strong and strong events. The events in the temperate monsoon zone are mainly moderate and weak events,(4) Trend analysis for the events shows that the annual average impacted area and intensity of the events are increasing during 1960-2013, whereas the duration of the events just changes little. This mean the events are becoming more severe in intensity and impacting more area. Significate positive trend of the events frequency is observed for the whole eastern china, but distinctive regional patterns existed. The events become more frequent in the tropical and subtropical monsoon zone, especially in the middle and low Yangzi river basin. Meanwhile, the increasing for all indices over this area is mainly due to the increase in very strong and strong events. The indices of overall event are decreasing in the temperate monsoon zone. Trends for different grade events vary: the moderate and weak events are increasing, while the very strong and strong events are decreasing.(5) Based on the grid observed precipitation dataset for 1970-2000, the performance of 6 models from the fifth phase of the Coupled Model Intercomparison Project(CMIP5) is evaluated in precipitation mean and extremes in the Middle and Low Yangtze River Basin(MLYRB). The performance for precipitation indices varies greatly. In general, the models simulate the precipitation mean and frequency better than the precipitation intensity and extremes. They also have difficulties capturing precipitation patterns over complex terrains. They tend to overestimate mean precipitations while underestimate the extremes.(6)The potential future changes of precipitation mean and extremes are also assessed. After correcting model biases, the multi-model ensemble mean(MME) is used to project changes for the years 2021-2050 and 2071-2100 relative to 1971-2000 under two emission scenarios: RCP 4.5 and RCP 8.5. Results show that with global warming, precipitation will become less frequent but more intense over the MLYRB. Relative changes in extremes generally exceed those in mean precipitation. Moreover, increased precipitation extremes are also expected even in places where mean precipitation is projected to decrease by the end of 21 st century. The overall increase in extreme precipitation could potentially lead to more frequent floods in this already flood prone region.