半干旱区春小麦农田干旱解除的降雨过程调控机制

The semi-arid area of China is one of the areas prone to drought disasters, and rainfall is one of the main ways to remove drought in this region. However, the current understanding of the regulation mechanism of rainfall process to drought relief is still limited. It is difficult to provide the basic support for accurate drought monitoring and forecasting and formulating scientific coping strategies, which seriously restricts the improvement of scientific drought disaster reduction level and disaster prevention and mitigation effect in the region. On the basis of the existing research, the project considering from two aspects of rainfall process (rainfall intensity, rainfall, rainfall duration and so on) and the characteristics of disaster tolerance (drought degree, farmland slope) selected Dingxi city with high incidence of drought in semi-arid area as the research area and the spring wheat field as the research object. The research method combining rainfall simulation control experiment and field encryption observation experiment would be adopted. And the direct continuous observation data such as soil moisture, crop water and crop physiological ecology would be obtained. Then starting from the process of rainfall process to the removal of spring wheat farmland drought, the project wants to understand the water process and physiological and ecological process characteristics of farmland-crop drought. At the same time, the in-depth study of the dynamic changes of various indicators threshold of drought relief and their interrelationship will be carried out. It is expected that this study will help to scientifically evaluate the ability of different precipitation processes to drought relief, promote the solution of scientific problems related to drought disaster research, and provide more effective technical support for drought disaster reduction work.

我国半干旱区是干旱灾害频发的地区之一，降雨是该区域解除干旱的主要途径之一。但是，目前降雨过程对干旱解除的调控机制认知仍然有限，难以为准确的干旱监测预报、制定科学应对策略提供基础支撑，严重制约着该区域科学抗旱减灾水平和防灾减灾效果的提高。本项目在已有研究的基础上。从降雨过程（降雨强度、降雨量、降雨时长等）和承灾体特征（干旱程度、农田坡度）两方面考虑，选择干旱频发的半干旱定西地区，以春小麦农田为研究对象，采取降雨模拟控制试验和大田加密观测试验相结合的研究方法，获取土壤水分、作物水分、作物生理生态等直接连续观测资料，从降雨过程对春小麦农田干旱解除的过程入手，认识农田-作物干旱解除的水分过程和生理生态过程特征，深入考察干旱解除的各种指标阈值的动态变化及其相互关联。期望这项研究有助于科学评价不同降水过程对干旱的解除能力，促进干旱灾害研究相关科学问题的解决，也可为抗旱减灾工作提供更有效的技术支撑。

降雨是半干旱区解除干旱的主要水分来源。研究半干旱区农田土壤水分时空格局对降雨的动态响应对揭示农业干旱解除调控机制具有重要意义。项目以半干旱春小麦农田为研究对象，基于3年模拟和长期土壤水分定位观测资料，研究了土壤水分和春小麦生理生态过程对降雨事件的响应特征，界定了干旱解除的指标阈值。结果表明：.土壤水分响应降雨的时间、深度等与土壤干旱程度、坡度和降雨强度密切相关。半干旱区春小麦农田降雨可以显著影响10-20cm的土层土壤水分；随着坡度增大，相同降雨过程引起的土壤水分增量呈降低趋势，入渗深度变浅；土壤水分入渗量与降雨强度、坡度以及二者交互作用均呈显著或极显著线性关系。在雨量相同的情况下，土壤水分的补给受雨强影响明显，当雨强在0.2-0.6L/m的范围时，土壤水分补给量随着雨强的增大而变小，变小幅度会随坡度的增加而变大，在相同雨强的情况下土壤水分补给量随着降雨量的增加而增加。.通过线性拟合得出春小麦农田干旱解除的临界雨强和雨量阈值指标。在0°坡度下，小雨、中雨和大雨解除重旱的降雨量分别为11、14和15mm，解除中旱分别为8、12和14mm，解除轻旱分别为4、6和7.5mm；在10°坡度下解除重旱的降雨量分别为16、24和46mm，解除中旱分别为12、21和41mm，解除轻旱分别为6、10和21mm；在20°坡度下解除重旱的降雨量分别为19、37和58mm，解除中旱分别为15、30和48mm，解除轻旱分别为7、15和24mm，上述阈值指标可直接用于业务或实践中指导农业抗旱救灾。界定了不同干旱程度和坡度下产生径流的临界降雨量阈值，0°坡度大雨强度下为20mm，10°坡度中雨强度和大雨雨强下分别为18.2-19.6mm和12.6-13.1mm；20°坡度分别为15.4-18.2mm和8.4-8.8mm。由中到大雨特别是大雨引起的坡度水土流失是半干旱春小麦农田不可忽视的生态问题。.春小麦生理生态指标对干旱解除过程的响应主要通过土壤水分改善实现的，光合、水分和生化参数随着土壤干旱解除均呈现“快-慢-平稳”的变化趋势，构建了指标响应干旱解除过程的模型方程，通过求突变点获得了不同参数变化的阈值。.本研究给出了不同干旱程度下干旱解除的量化指标，这对改进现有各类干旱指数、评价干旱影响程度和农业抗旱救灾将有较高的科学参考价值。