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Lake-Effect Rainfall over Three East African Lakes

东非三个湖泊的湖泊效应降雨

基本信息

批准号：
1850661
负责人：
Sharon Nicholson
金额：
$ 64.02万
依托单位：
Florida State University
依托单位国家：
美国
项目类别：
Standard Grant
财政年份：
2019
资助国家：
美国
起止时间：
2019-07-15 至 2024-06-30
项目状态：
已结题

来源：
https://www.nsf.gov/awardsearch/showAward?AWD_ID=1850661&HistoricalAwards=false
关键词：
Lake Effect Rainfall over Three

项目摘要

This project is an examination of lake effect rainfall over three of the African Great Lakes: Lake Victoria, Lake Tanganyika, and Lake Turkana. These lakes are an essential resource for East Africa, providing fisheries, fresh water, and hydroelectric power to Tanzania, Kenya, and Uganda, and Lake Victoria also contributes to the flow of the Nile. Lake Victoria has a round shape and much larger surface area than Tanganyika and Turkana, which are long narrow rift valley lakes. But despite their differences in size, shape, and setting, all three experience lake effect rainfall, or an enhancement of rainfall over the lake relative to its surroundings. The lake effect is particularly intense over Victoria, where it takes the form of nighttime thunderstorms accompanied by strong winds and high waves. The thunderstorms create a severe hazard for the fishing fleet, claiming between three and five thousand lives every year. In addition to the thunderstorm hazard, lake effect rain is of interest for its contribution to the water balance of the lakes, which have suffered declining water levels resulting in hardship for nearby populations. There have been few attempts to estimate the contribution of over-lake rainfall to variability and trends in lake water level, and existing studies have considerable uncertainty.The goal of this project is to provide a detailed climatology of the rainfall regimes over the lakes and to examine the meteorological factors that modulate these regimes, with particular attention to the relationship between over-lake rainfall and regional-scale winds. Specific objectives are to 1) develop quantitative statistics on over-lake rainfall, including magnitude, diurnal cycle, seasonality of occurrence, interannual variability, and relationship to rainfall in the catchment and/or surrounding land; 2) establish the meteorological controls on over-lake rainfall; 3) assess recent changes in the rainfall regime over the lakes, perhaps as a result of anthropogenic changes such as increased lake temperature; and 4) determine whether the changes are commensurate with changes in the surrounding catchment or land.Although lake effect precipitation is the common thread in the research, preliminary results suggest that the mechanisms of over-lake rainfall enhancement may differ from one lake to another. Over Lake Victoria, with its large surface area and siting within a topographic depression, rainfall enhancement could result from simple land breeze dynamics, in which winds converge over the lake at night when the hillslopes cool but the lake is still warm (up to 3.5C warmer than its shores). Rainfall enhancement over Lake Tanganyika is less pronounced and is limited to the wet season, with two distinct maxima over the lake. These characteristics lead the PI to hypothesize that over-lake rainfall is controlled primarily by the interaction of large-scale wind and topography rather than downslope winds and land breezes. The PI further hypothesizes that rainfall over Lake Turkana is influenced by both the slope winds that develop around Lake Victoria and by the strong low-level jet that flows through the Turkana gap. The implications of these mechanisms for the variability of over-lake rainfall and its likely response to climate change is examined as part of the project. The work is conducted using a variety of observational datasets including a rain gauge dataset compiled by the PI and others, satellite data from the Global Precipitation Measurement Mission, and surface winds from spaceborne scatterometers.The work is of societal interest due to the importance of the lakes for East Africa, the hazards posed by severe over-lake convection, and the relevance of the lake effect mechanisms for anticipating the future evolution of lake levels in a changing climate. Results of the work are communicated to stakeholders through local organizations, for instance ACLENet and the Nile Basin Initiative. The project also develops datasets of interest to researchers and decision makers including detailed climatologies of over-lake rainfall and surface winds at high spatial and temporal resolution. The project also provides support and training for a graduate student.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.

这个项目是对三个非洲大湖：维多利亚湖、坦噶尼喀湖和图尔卡纳湖的湖泊效应降雨的研究。这些湖泊是东非的重要资源，为坦桑尼亚、肯尼亚和乌干达提供渔业、淡水和水力发电，维多利亚湖还为尼罗河的流动做出了贡献。维多利亚湖呈圆形，表面积比坦噶尼喀湖和图尔卡纳湖大得多，这两个湖都是狭长的裂谷湖泊。但是，尽管它们在大小、形状和环境上存在差异，但这三个湖泊都经历了湖泊效应降雨，或者湖泊上的降雨量相对于周围环境的增强。湖泊效应在维多利亚州尤为强烈，夜间雷暴伴随着强风和巨浪。雷暴给捕鱼船队带来了严重的危险，每年夺去三到五千人的生命。除了雷暴灾害之外，湖效应降雨对湖泊水平衡的贡献也令人感兴趣，这些湖泊的水位下降导致附近人口的困难。很少有人尝试估计湖上降水对湖泊水位变化和趋势的贡献，现有的研究具有相当大的不确定性。该项目的目标是提供湖泊上降雨情况的详细气候学，并检查调节这些情况的气象因素，特别注意湖上降雨与区域尺度风之间的关系。具体目标是：1)制定湖上降雨的数量统计，包括大小、日周期、发生的季节性、年际变化以及与集水区和/或周围土地降雨的关系；2)建立湖上降水的气象控制；3)评估湖泊降雨状况的近期变化，这可能是人为变化（如湖泊温度升高）的结果；4)确定这些变化是否与周围流域或土地的变化相称。虽然湖效应降水是研究的主线，但初步结果表明，湖上降水增强的机制可能因湖而异。在维多利亚湖上，由于其面积大且位于地形洼地内，降雨增加可能是由简单的陆风动力学造成的，在夜间，当山坡凉爽时，风聚集在湖面上，但湖泊仍然温暖（比湖岸温暖3.5摄氏度）。坦噶尼喀湖的降雨增强不那么明显，仅限于雨季，湖面上有两个明显的最大值。这些特征使PI假设湖上降雨主要由大尺度风和地形的相互作用控制，而不是由下坡风和陆风控制。PI进一步假设，图尔卡纳湖的降雨受到维多利亚湖周围形成的斜坡风和流经图尔卡纳空隙的强烈低空急流的影响。这些机制对湖上降雨变异性的影响及其对气候变化的可能反应是该项目的一部分。这项工作是利用各种观测数据集进行的，包括由PI等编制的雨量计数据集，全球降水测量任务的卫星数据，以及星载散射计的地面风。由于湖泊对东非的重要性，严重的湖上对流造成的危害，以及湖泊效应机制在气候变化中预测湖泊水位未来演变的相关性，这项工作引起了社会的兴趣。工作结果通过当地组织，例如ACLENet和尼罗河流域倡议，传达给利益相关者。该项目还开发了研究人员和决策者感兴趣的数据集，包括高时空分辨率的湖上降雨和地面风的详细气候学。该项目还为研究生提供支持和培训。该奖项反映了美国国家科学基金会的法定使命，并通过使用基金会的知识价值和更广泛的影响审查标准进行评估，被认为值得支持。