半干旱区作物干旱致灾过程特征及其若干阈值研究

China is one of the countries with most frequent drought, and drought disaster prevention and mitigation is always the important mission of Chinese. For the influence of climate change and growing water resource demand, the global droughts are exacerbating, which will make new challenges to the drought prevention and mitigation in China. However, scientific problems that how to define the beginning and end time of the drought events, and how to quantify the drought severity has not been answered well, which restrict seriously the improvement of achievements in drought prevention and mitigation scientifically. . The averaged time state and cross-section state of drought events has been focused in the past researches. This study, besides this, will introduce the comparative test of field drought simulation, corresponding observational data of soil moisture, farmland evapotranspiration, crop physiological-ecological characteristics and meteorology directly, to analyze the drought. The primary aim of this study is to examine the process characteristics of disasters induced by drought, and then describe the continuous development of disasters, and determine several thresholds of drought indices, such as the index of crop-specific, soil moisture and farmland evapotranspiration. Moreover, the effects of meteorological factors on disasters process induced by drought will be analyzed, and the difference of several drought indexes and its cause in the assessment of crop drought in the semi-arid area will be also investigated. . The study results will provide some helps for the scientific problem resolution on quantifying the drought severity and continuous development of disasters; and make some contributions to disaster prevention and mitigation in China.

我国是全球干旱灾害发生最频繁的国家之一，抗旱减灾是我国防灾减灾工作的重要任务。受气候变化和水资源需求增加的影响，全球干旱灾害加剧，这对我国抗旱减灾工作提出了新的挑战。但是，如何确定干旱灾害开始和结束时间、量化旱灾严重程度等科学问题仍没有很好解决，严重制约着我国科学抗旱减灾工作水平和防灾减灾效果的提高。. 本项目在已有主要关注于干旱灾害事件的时间平均状态和断面研究的基础上，通过农田干旱模拟对比试验，获取土壤水分、农田蒸散、作物生理生态、基本气象等直接观测资料，从半干旱区作物干旱致灾过程入手，研究作物特征指标、土壤水分和农田蒸散描述作物干旱灾害持续发展和阈值变化特征，分析气象因子对干旱致灾过程的影响规律，考察几种干旱指数评估半干旱区作物干旱灾害的差异及成因。. 期望这项研究对解决定量描述作物干旱灾害严重程度、持续发展特征等科学问题有所帮助，并对我国科学抗旱减灾工作有所贡献。

抗旱减灾是我国防灾减灾工作的重要任务。但是， 如何确定干旱灾害开始时间、量化旱灾严重程度等科学问题仍没有很好解决。本项目拟就半干旱区作物春小麦干旱致灾过程特征、阶段阈值等开展研究。.结果表明，在供水正常情况下， 春小麦净光合速率、叶片含水率、蒸腾速率、土壤相对湿度、农田蒸散均随时间的持续呈波动变化，各指标波动均值都维持在较高水平。当受到干旱胁迫时，这些指标均开始低于正常生长情况下的各种指标均值，并随时间的持续逐渐减小。.从正常供水到干旱胁迫与持续，春小麦净光合速率、蒸腾速率、叶片含水率、农田蒸散都随土壤相对湿度的减小呈现上下波动而后快速线性减小趋势（P<0.001），存在一个明显的阶段变化和转折点，在大于转折点值时，各指标值随土壤相对湿度的减小表现为波动变化；在小于转折点值时，随土壤相对湿度的减小表现为持续减小，但减小速度有一定的差异。各生物指标转折点对应的土壤相对湿度值有围绕平均值上下波动特征，即春小麦干旱致灾开始土壤相对湿度阈值是基本一致的，约为50%。而春小麦农田蒸散量转折点对应的土壤相对湿度值在70.5-72.8%之间。基于这种变化特征，分别给出了基于土壤相对湿度、生物和农田蒸散指标的春小麦普通干旱过程和快速干旱过程阶段阈值。.随着干旱持续，春小麦适宜上限温度、光饱和点和二氧化碳饱和点存在下移现象；降水或灌溉，直接改变农田土壤水分状况，进而减缓和解除干旱致灾过程；温度、太阳辐射、风速增大导致农田蒸散增大、土壤水分减小，加速干旱致灾过程进程。.与干旱持续过程指标阈值比较，基于土壤相对湿度的传统干旱指标略偏高，总体看有一致性；而与其它传统指数可比意义不大。对于作物受害状况而言，干旱持续过程指标阈值为定量描述且有较好的跨区域、跨品种一致性。.本研究给出了干旱不同阶段作物受危害情况的量化指标，这对改进现有各类干旱指数、确定干旱指标或阈值将有较高的科学参考价值。