增温和降水集中度及雨强变化对西北地区东部干旱的影响研究

Drought is one of the most damaging climate-related hazards,and it has significantly damage on agricultural production and the natural environment, particularly in water scarce regions.The frequency and intensity of droughts are likely to change rapidly under global warming.There fore, numerous scientists and governments have focused on studying the drought and factors causing drought.. Although precipitation deficits are often the primary cause for historical droughts, it is also has a significant importance to investigate precipitation concentration and precipitation intensity due to their great impact on droughts. And the rising temperatures under a warming climate are also considered as a major cause for the widespread drying. Many studies on changes in drought, precipitation and temperature and their relationships have been conducted. these studies mainly focused on the precipitation amount and the range of rising temperature,few studies have considered the effects of precipitation concentration,precipitation intensity and the effects of the rising temperature in different periods on drought.what about the response of drought to the significant and complex change of these factors in the east of northwest China? . Based on daily meteorological data and several statistical methods,the changing characteristics of temperature, precipitation concentration and precipitation intensity in the east of northwest China will be analyzed in this project, and more attention and research will be given on the impact of changes in precipitation concentration, precipitation intensity and the rising temperature in different periods on the drought ,the relationship between precipitation intensity, precipitation concentration with droughts will be explored. Through the method of the slope changing ratio of cumulative quantity, the contribution of precipitation and temperature to the dryness process will be evaluated quantitatively,and the dominant factor which lead to the process will be identified.the difference of contribution and dominant factor will be also revealed.Meanwhile,the relationship between precipitation concentration, precipitation intensity, the rising temperature and the atmospheric circulation will be revealed.Through these analysis,the relationship between global warming and the changes of drought-causing factors , and the relationship between drought-causing factors and drought will be explored quantitatively and comprehensively.The results not only can deepen the understanding of the evolution and causes of drought in the study area under the background of global warming, but also can provide a scientific basis for drought monitoring, forecasting,early warning and climate impact assessment.

干旱影响因子的精准识别与量化评估是科学、准确地开展干旱监测和研究的基础。本项目突破以往探讨干旱时单纯关注降水量和增温幅度变化对干旱的影响的局限，关注到降水集中度、雨强以及不同时期增温对干旱的影响，从多维角度探讨降水量、降水集中程度、降水强度以及不同时段的增温与干旱的关系，定量评估增温和降水变化对干旱的影响程度，探讨干旱对降水集中度、雨强以及增温变化的综合响应机制。同时，对比分析不同降水集中度、雨强和增温下后期干旱发生与否对应的环流形势、低层水汽输送条件之间的异同，揭示降水集中度、雨强和增温的变化与大气环流之间的联系，加深认识和理解干旱形成的物理机制。该项目的开展将有助于增进气候变化与干旱影响因子、干旱影响因子与干旱变化之间关系的深入理解，可为区域干旱影响因子的科学构成与量化评估的提供科学指导，对于区域干旱监测、预测预警以及防灾减灾具有重要的科学指导意义。

干旱灾害是我国乃至全球最常见、危害最严重的气象灾害，西北地区东部地处欧亚大陆腹地，水资源相对匮乏，是中国最容易发生干旱灾害的区域。本项目重点关注变暖背景下降水集中度、雨强以及增温对西北地区东部干旱的影响，从多维角度探讨降水量、降水强度、降水频率、降水聚集度变化以及增温与干旱的关系，定量评估增温和降水变化对干旱的影响程度。研究表明：近58年来，西北地区东部基本趋于干旱化，春季和秋季干旱化最严重，夏季和冬季，研究区东部陕西中南部和甘肃陇东区域趋于湿润，其余区域仍趋于干旱。蒸散变化对区域干湿变化影响最大，贡献基本都大于降水，尤其是春季。研究区东部和中北部区域年干旱过程次数较其余地区多，平均每年有2~3次干旱过程，尤其是陕北和关中一带。干旱过程平均持续时间在2个月左右。春旱所占比例明显高于其他类型，两季连旱所占的百分比平均为7%，三季连旱仅占1%-4%，其中，夏秋冬三季连旱略多于其他类型。研究区北部区域降水不均匀性较大。四季中，夏季降水较为均匀，其他三季降水集中度较高且区域差异明显。近58年西北地区东部的年和各季均表现为一致的增温趋势，春、夏、秋三季降水不均匀性增大，冬季降水集中度显著减小；集中期在前后1侯间摆动，局地集中期显著退后；冬季弱降水日数变化不显著，其他三季降水日数也呈减少趋势，尤其是夏秋两季。干旱过程强度与增温的关系不显著，降水非均匀性对干旱强度的影响远大于时段内的降水量亏缺程度的影响。降水非均匀性对干旱的影响在春夏季尤为显著，当春夏季集中度高，集中期晚的情况下有7成以上的时候会发生干旱，其中有3成是在降水偏多的情形下，部分区域有近5成是在降水偏多情形下，此时降水集中度一般在0.4以上。该成果将有助于增进气候变化与干旱影响因子、干旱影响因子与干旱变化之间关系的深入理解，可为区域干旱影响因子的科学构成与量化评估的提供科学指导，对于区域干旱监测、预测预警以及防灾减灾具有重要的科学指导意义。

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