Collaborative Research: on the causes of recent trends in precipitation over La Plata basin and their impact on the basin's hydrology

拉普拉塔是南美洲第二大河流，其支流是南美洲南部的生命血液。拉普拉塔在布宜诺斯艾利斯附近河口的年平均流量大于密西西比河。 水电装机容量（主要在巴拉那河，一个主要的子流域）超过20 000兆瓦，几乎是哥伦比亚河流域的两倍，哥伦比亚河流域是迄今为止美国河流中水电产量最大的河流。另一方面，该区域易受大规模洪水的影响，造成生命和财产损失，在上个世纪，南美洲南部大部分地区，特别是拉普拉塔盆地，降水和其他陆地地表水循环变量经历了非常大的十年尺度变化。 在过去的30年里，拉普拉塔盆地中部的降水量增加了30-40%，重要的科学问题已经出现：这些变化的原因是什么？降水量的变化如何与径流量的变化联系在一起？ 到目前为止，还没有确切的证据来解释这种变化的原因。一个由北美和南美水文学家和大气科学家组成的小组已经聚集在一起，以解决该盆地区域水循环的这一关键和独特的方面。这项研究要解决的首要科学问题是：“在观测到的拉普拉塔盆地降水和径流的年际至十年尺度变化中，当地效应的重要性是什么？“具体而言，将力求：（a）评估区域气候模拟捕捉1970年代拉普拉塔盆地降水变化的程度;（B）估计当地强迫的影响（例如，土壤湿度、植被）对拉普拉塔盆地降水和地表水文的影响;（c）确定盆地局部效应和大尺度降水变化的作用，本建议概述的研究战略是以诊断分析和用大气区域中尺度Eta模式和维克国际中心水文模式以耦合和非耦合模式进行的数值试验为基础。埃塔模式，加上维克和河流路由方案，将被用来描述从远程和/或本地强迫的河流流量的变化的途径。实验旨在了解土地利用变化对长期气候的影响，以及土地利用/土地覆盖与降水和河流流量之间的反馈。实验还将集中在大尺度变化影响区域降水的机制上，这项研究的相关性不仅是因为它将解决尚未回答的科学问题，而且还因为它是发展中国家地区水资源的一个明确的应用。这一办法旨在以一致的方式处理大气和水文问题。该提案有很强的教育成分。学生将直接参与研究;来自南美洲大学的科学家将参与增加区域专业知识，但也加强教育部分。 计划与南美洲的学生进行交流，并计划在布宜诺斯艾利斯大学开设一至两门相关课程（本项目不承担任何费用），这一建议利用了马里兰州大学和华盛顿大学的现有基础设施。计算机系统已经到位，所需的升级将在本项目开始时准备就绪。

Berbery/Lettenmaier0450089/0450209La Plata is the second largest river in South America and its tributaries are the life blood of the southern part of the continent. La Plata has an annual-mean discharge at its mouth near Buenos Aires larger than that of the Mississippi. The installed hydropower generating capacity (mostly in the Parana, a major subbasin) exceeds 20,000 MW, almost double that of the Columbia River basin, which by far has the largest hydropower production among U.S. rivers. On the other hand, the region is vulnerable to large scale floods with losses of life and damages to property.Precipitation and other land surface water cycle variables have undergone very large decadal scale changes over the last century in much of the southern part of South America, and within La Plata Basin in particular. In the last thirty years, precipitation increased up to 30-40% over the central La Plata basin, and important scientific questions have emerged: what are the reasons for these changes, and how are variations in precipitation linked to streamflow changes? Up to now, no certain evidence has been offered to explain the reasons for such changes.A team of North and South American hydrologists and atmospheric scientists has been assembled to address this crucial and unique aspect of the basin's regional water cycle. The overarching scientific question to be addressed by this research is: "What is the importance of local effects in the observed interannual-to-decadal scale changes in La Plata Basin precipitation and streamflow?" Specifically, it will be sought to: (a) Assess the degree to which regional climate simulations capture the precipitation changes in the 1970's over La Plata Basin; (b) Estimate the effects of local forcings (e.g., soil moisture, vegetation) on the precipitation and surface hydrology of La Plata Basin; (c) Identify the role of local effects and large scale precipitation variability in the basin.The research strategy outlined in this proposal is based on diagnosis analysis and numerical experiments with the atmospheric regional mesoscale Eta model and the VIC hydrologic model, in coupled and uncoupled mode. The Eta model, coupled with VIC and a river routing scheme, will be employed to describe the pathways from remote and/or local forcings to the changes in river discharge. Experiments are designed to understand the impacts of land use changes on the longer term climate and the feedbacks between land use/land cover and precipitation and river discharge. Experiments will also focus on the mechanisms by which large scale variability affects the regional precipitation.The relevance of this research is not only due to the yet unanswered scientific questions it will address, but also because it is a defined application for water resources of a region of the developing world. The approach aims at having the atmospheric and hydrologic problems treated in a consistent manner. The proposal has a strong educational component. Students will be directly involved in the research; scientists from Universities of South America will participate adding regional expertise but also enhancing the educational component. Plans are in place for exchanges with students of South America, and one or two related courses at the University of Buenos Aires are planned (at no cost to this project).This proposal takes advantage of available infrastructure both at the University of Maryland and the University of Washington. Computer systems are already in place and needed upgrades will be ready by the time this project starts.