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Drought is one of the main disasters causing agricultural production losses. Accurate and effective agricultural drought monitoring is of great significance to reduce agricultural production losses. In this study, the standardized soil moisture index for agricultural drought evaluation was established by using the historical time series of soil moisture. Based on the index, the temporal and spatial distribution of drought events in the Luanhe River Basin from 2002 to 2019 were analyzed, and the agricultural drought was quantitatively evaluated. The results showed that soil moisture of most grid units in the Luanhe River Basin obeyed normal distribution during the study period, and that the soil moisture of a few grid units obeyed generalized extreme distribution. The changes of drought and flood in each grid unit had good temporal consistency, that is, the changes of drought and flood was consistent. The changes of drought and flood in the middle of the basin was relatively significant, while the agricultural drought generally showed a trend of reduction. The spatial distribution of agricultural drought severity was not obvious. Relatively speaking, the drought characteristics (the frequency, duration and intensity of drought) were higher in the middle and northwest of the basin and lower in the southeast. The results could provide a reference for agricultural drought prediction and the formulation of drought prevention and mitigation measures in the Luanhe River Basin.干旱是造成农业生产损失的主要灾害之一,及时、准确地监测农业干旱对于降低作物生产损失具有重要意义。本研究基于土壤含水量历史时间序列数据构建了标准化土壤湿度指数,分析了滦河流域2002—2019年干旱时空分布变化规律,并对农业干旱进行定量评价。结果表明: 研究期间,滦河流域内大部分栅格单元土壤含水量在时间上以正态分布为主,少部分栅格单元为广义极值分布。各栅格单元在时间上的旱涝变化具有良好的一致性,即呈现一致的变旱或变涝,且流域中部旱涝变化相对显著,农业干旱总体呈减轻趋势。滦河流域农业干旱严重程度的空间分布不明显,其中,流域中部和西北部各干旱特征值(干旱发生频率、干旱历时及干旱烈度)较高,东南部较低。本研究结果可为滦河流域农业干旱预测和防旱减灾措施的制定提供参考依据。.

Calculation of design drainage modulus is of great importance for the safety of farmland and reduction of waterlogging loss. We investigated the effects of main meteorological factors on design farmland drainage modulus by focusing on a closed farmland area in Ninghe District of Tianjin City. To resolve the problem of limited observation, the parameter sensitivity was analyzed according to mutual information and partial rank correlation coefficient aiming at the total runoff depth based on field observation experiment. The reasonable parameters were obtained by combining with soil water content and the relative variation of groundwater level. Then, a three-source runoff yield model coupling of excess infiltration and saturation was established to estimate runoff and design drainage modulus, and the effects of meteorological factors such as precipitation and evaporation on drainage modulus were analyzed. Results showed that summer precipitation significantly reduced and evaporation varied a little during 1960-2015. The corresponding drainage modulus decreased with the reduction of precipitation. When return period increased, the magnitude of the reduction in precipitation as well as the design drainage modulus increased. However, the effects of meteorological factors on design drainage modulus was generally inapparent. Thus, we concluded that the current drainage modulus is suitable for the study area.设计排涝模数的计算对农田安全和有效降低涝灾损失意义重大.本文选取天津市宁河区封闭农田小区为研究对象,分析了主要气象因子对农田设计排涝模数的影响.为解决观测样本有限的问题,在现场观测试验的基础上,以总径流深为目标,使用互信息、偏秩相关方法分析了参数敏感性,结合土壤含水量、地下水位相对变化量得到了合理的模型参数,建立了三水源超渗-蓄满耦合产流模型,进行了产流量和设计排涝模数估算,并分析了降雨和蒸发等气象因子对设计排涝模数的影响.结果表明: 1960—2015年,研究区夏季降水量显著减少,蒸发量变化不明显.排涝模数随降水量减少而减少,且随着设计重现期的增大,降水和设计排涝模数的减少量均有所增大,但总体来讲,气象因子对设计排涝模数的影响并不大,现行设计排涝模数可不进行修订.

Methanol decomposition over alkali-leached Ni3Sn powder at 513–793 K was investigated. Compared with untreated Ni3Sn, alkali-leached Ni3Sn had high catalytic activity and selectivity toward H2 and CO production above 633 K. A maximum H2 production rate of 100 × 10−3 mol h−1 g-Cat−1 and H2 selectivity above 95% were attained over alkali-leached Ni3Sn at 793 K. Alkali-leached Ni3Sn presented good catalytic activity for 45 h of reaction at 713 K, whereas Ni3Sn had none. The activation energy was calculated, and its values rapidly decreased from Ni3Sn to alkali-leached ones. The improvement was attributed to the formation of Ni nanoparticles less than 100 nm in diameter in the alkali-leaching process, which had high activity for methanol decomposition. The improved catalytic activity favored the gradual formation of fine Ni3Sn particle during the reaction, which served as the active sites for methanol decomposition when the catalytic activity decreased because of carbon deposition on the Ni surface. Results demonstrated that alkali-leached Ni3Sn was a promising potential catalyst for hydrogen production from methanol.