Improving evapotranspiration estimation models through quantitative watershed parameter analysis and remote sensing applications

Numerous models had been developed to predict the annual evapotranspiration (ET) in vegetated lands across various spatial scales. Fu's (Scientia Atmospherica Sinica, 5, 23–31) and Zhang's (Water Resources Research, 37, 701–708) ET simulation models have emerged as highly effective and have been widely used. However, both formulas have the non-quantitative parameters (m in Fu's model and w in Zhang's model). Based on the collected 1789 samples from global long-term hydrological studies, this study discovered significant relations between m (or w) and vegetation coverage or greenness in collected catchments. Then, we used these relations to qualify the parameters in both Zhang's and Fu's models. Results show that the ET estimation accuracies of Fu's (or Zhang's) model are significantly improved by about 13.49 mm (or 6.74 mm) for grassland and cropland, 38.52 mm (or 29.84 mm) for forest and shrub land (coverage<40%), 19.74 mm (or 16.17 mm) for mixed land (coverage<40%), respectively. However, Zhang's model shows higher errors compared with Fu's model, especially in regions with high m (or w) values, such as those with dense vegetations or P/E₀ (annual precipitation to annual potential ET) smaller than 1.0. Additionally, this study also reveals that for regions with vegetation cover less than 40%, the annual ET is not only determined by vegetation types, but also relates to the sizes of vegetation-covered areas. Conversely, for regions with vegetation cover more than 40%, the annual ET is mainly determined by the vegetation density rather than vegetation types or vegetation coverage. Thus, linking m (or w) parameters with vegetation greenness allows leveraging remote sensing for forest management in data-scarce areas, safeguarding regional water resources. This study pioneers integrating vegetation-related indices with basin parameters, advocating for their crucial role in more effective hydrological modelling.     

基于MODIS时序影像的湖南省油菜种植面积遥感监测分析

基于时间序列影像数据的提取方法可实现快速监测大面积农作物的种植分布和面积估算.以湖南省为研究区,利用2017年500 m空间分辨率的MODIS NDVI时序数据,结合湖南省耕地分布数据和实地样点数据得到油菜物候标准曲线,采用最小二乘法与阈值法提取得到湖南省油菜种植分布.结果显示,遥感提取得到的湖南省油菜种植面积主要分布...     

对流层顶折叠检测新方法及其在中纬度 灾害性天气预报中的应用

对流层顶折叠是中纬度地区对流层上层—平流层下层区域(简称UT/LS)内的一个重要的大气现象,它与气旋生、暴雨强对流触发以及降水增幅密切相关。由于这些天气条件下的大气状况异常复杂,因此目前国际上普遍采用的基于干大气条件的对流层顶折叠检测方法存在很大局限性。本文在借鉴已有的卫星资料和数值预报相结合的模式识别法的基础上,通过统计分析的方法建立了高层大气水汽与广义湿位涡、臭氧浓度的关系以及对流层顶折叠与高空急流的位置关系,同时考虑了动力对流层顶高度在判识过程中的辅助作用,建立了一套基于FY-2E静止气象卫星遥感数据的,适用于与暴雨强对流有关的对流层顶折叠动态监测新方法。在利用FY-3A和FY-3B反演的臭氧总量、臭氧垂直廓线以及ECMWF Interim资料计算的位涡等资料对算法进行精度验证的基础上,将该方法在2012年7月21日北京特大暴雨天气过程以及2013年5月14~17日华南大暴雨天气过程的监测和分析上进行了应用,并取得了较好的效果。从应用效果看,本文提出的这种对流层顶折叠识别方法是合理可行的,并具有一定的应用价值,可为中纬度地区暴雨强对流天气的监测和预警提供参考指标。     

Response of Vegetation Cover Change to Drought at Different Time-scales in the Beijing-Tianjin Sandstorm Source Region,China

Dominated by an arid and semiarid continental climate, the Beijing-Tianjin Sandstorm Source Region(BTSSR) is a typical ecologically fragile region with frequently occurring droughts. To provide information for regional vegetation protection and drought prevention, we assessed the relations between vegetation cover change(measured by the Normalized Difference Vegetation Index,NDVI) and the Standardized Precipitation Evapotranspiration Index(SPEI) at different time-scales, in different growth stages, in different subregions and for different vegetation types based on the Pearson's correlation coefficient in the BTSSR from 2000 to 2017. Results showed that 88.19% of the vegetated areas experienced increased NDVI in the growing season; 48.3% of the vegetated areas experienced significantly increased NDVI(P 0.05) and were mainly in the south of the BTSSR. During the growing season, a wetter climate contributed to the increased vegetation cover from 2000 to 2017, and NDVI anomalies were closely related to SPEI. The maximum correlation coefficient in the growing season(Rmax) was significantly positive(P 0.05) in 97.84% of the total vegetated areas. In the vegetated areas with significantly positive Rmax, pixels with short time-scales(1–3 mon) accounted for the largest proportion(33.9%).The sensitivity of vegetation to the impact of drought rose first and then decreased in the growing season, with a peak in July. Compared with two subregions in the south, subregions in the north of the BTSSR were more sensitive to the impacts of drought variations,especially in the Xilingol Plateau and Wuzhumuqin Basin. All four major vegetation types were sensitive to the effects of drought variations, especially grasslands. The time-scales of the most impacting droughts varied with growth stages, regions, and vegetation types.These results can help us understand the relations between vegetation and droughts, which are important for ecological restoration and drought prevention.     

甘肃中部地区飞机积冰的气象条件分析

利用3a空中观测资料和机载仪器采集资料分析了影响飞机积冰的气象条件,总结了飞机积冰的一般规律。分析结果表明：飞机积冰在水汽充沛地域发生较多;通常飞机积冰形成于温度低于0℃的云中,出现积冰的温度范围在0～-11℃,而出现较强积冰的温度范围在-1--18℃;云中过冷水含量越大,积冰强度也越大。     

临夏盆地巴谢河流域晚更新世以来滑坡发育历史重建

晚更新世以来,特别是全新世以来,黄土高原西北部发育了多期次的滑坡事件。临夏盆地巴谢河流域较好地保留了多期次滑坡的遗存,有研究历史滑坡发育规律的良好素材。文章通过详细的野外调查,初步厘清了滑坡空间分布及新老滑坡相互叠置关系,总结得到本地区滑坡的四种发展类型:压裂型深层黄土-泥岩滑坡、滑移型深层黄土-泥岩滑坡、蠕变型中浅层黄土-泥岩滑坡和塌滑型黄土滑坡。不同时期发育的滑坡在野外呈现明显不同的特征:发育于晚更新世的古滑坡有圈椅状的地形和高陡的后缘陡壁,滑坡堆积体已固结,堆积体表面冲沟发育;发育于全新世早期的老滑坡除了具有圈椅状地形和高陡后壁外,堆积体较为松散,堆积平台形态较为完整;发育于全新世晚期的新滑坡则保留了更多的滑坡特征,可见滑坡后缘和侧缘裂缝。巴谢河流域滑坡大多有多次滑动的迹象,不同期次的滑坡相互重叠,在同一范围发生多次滑动,形成多级滑坡堆积平台。滑坡埋压动植物、滑坡洼地短期水体沉积物等有着明显的滑坡指示意义。通过采集此类样品,利用14C和光释光等测年手段,获取了本地区一系列滑坡事件的年龄。对测年数据进行统计分析,得到巴谢河流域晚更新世以来的五个滑坡高发时段,分别为100~63 kaBP、45.2~41.5 kaBP、33.3~28.2 kaBP、22.5~15.2 kaBP和10.4~0.2 kaBP。以上滑坡高发时段的推断将为认识去环境变迁提供证据。     

水文水深数据修正的普里兹湾数字水深模型

在第一版国际南大洋地图集(the International Bathymetric Chart of the Southern Ocean Version 1.0,IBCSO V1)的基础上,利用现场水文观测中的水深数据重构了普里兹湾及其周围海域的海底地形,建立了更准确的高分辨率数字水深模型。从多套现场水文观测数据中提取了水深观测结果,去除重复剖线后,比较了水文观测中的水深数据与IBCSO V1在500 m×500 m网格上的差异。在保留IBCSO V1中原始多波束、单波束回声测深数据和其他水深观测数据的前提下,使用插值技术修正了无观测数据海域地形。基于大量的海豹观测数据在较大程度上订正了IBCSO V1海床深度。与IBCSO V1海床深度相比,从戴维斯站以东至82°E的南极大陆沿岸、埃默里冰架前缘西部以及西冰架前缘附近区域的海床深度被低估的可能性最大。优化的南极普里兹湾海域水深数字地图改进了对普里兹湾海底地形结构特征的认识。更加准确的地形数据有利于理解海底地形对普里兹湾海洋环流的影响和建立更加可靠的数值模型。     

考虑降水预报的三峡入库洪水集合概率预报方法比较

为了考虑预见期内降水预报的不确定性对洪水预报的影响,采用中国气象局、美国环境预测中心和欧洲中期天气预报中心的TIGGE(THORPEX Interactive Grand Global Ensemble)降水预报数据驱动GR4J水文模型,开展三峡入库洪水集合概率预报,分析比较BMA、Copula-BMA、EMOS、M-BMA 4种统计后处理方法的有效性。结果表明:4种统计后处理方法均能提供一个合理可靠的预报置信区间;其期望值预报精度相较于确定性预报有所提高,尤其是水量误差显著减小;M-BMA方法概率预报效果最佳,它能够考虑预报分布的异方差性,不需要进行正态变换,结构简单,应用灵活。     

Spatial distribution of trace elements associated with organic carbon along the Beiyun River basin,Beijing,China

Pollution resulting from terrestrial and aquatic trace elements has become a severe problem across the world. Organic carbon(OC) content has a high affinity for metallic contaminants and it acts as a significant sink for trace elements. The decomposition of OC content directly influences the bioavailability of trace elements. The decomposition of OC content and OC distribution vary spatially, these processes affect the release of trace elements and need further research. In the current study, se...