Quantifying the Relative Roles of Progressive Land Use Change, Irrigation, and Remote Forcing in Southern Great Plains Precipitation Variability

量化渐进式土地利用变化、灌溉和远程强迫对南部大平原降水变化的相对作用

• 批准号: 1355916
• 负责人: Matthew Van Den Broeke
• 金额: $ 44.67万
• 依托单位: University of Nebraska-Lincoln
• 依托单位国家: 美国
• 项目类别: Standard Grant
• 财政年份: 2014
• 资助国家: 美国
• 起止时间: 2014-07-01 至 2018-06-30
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=1355916&HistoricalAwards=false
• 关键词: Quantifying; Relative; Roles; Progressive; Land

This project seeks to understand the causes of precipitation variability in the US Southern Great Plains (SGP), roughly equivalent to the region covered by Nebraska, Missouri, Oklahoma, Arkansas, Texas, and Louisiana. This area is among the most drought-prone in the US, with substantial economic impacts including the severe consequences of the Dust Bowl and losses in the tens of billions of dollars in 2011 and 2012. Precipitation anomalies in the region, including rainfall deficits contributing to droughts, are generally attributed to changes in the large-scale atmospheric circulation brought about by fluctuations in sea surface temperature (SST). But local land surface conditions can act to intensify remotely-forced precipitation variability through several mechanisms. For instance, lack of rainfall leads to dry soil and reduced evaporation, which reduces the moisture source available for precipitation and causes further rainfall reduction. Also, warm dry conditions due to drought promote ridging in the mid-troposphere, which can further reduce precipitation as rain-bearing systems move around the ridge. This project considers the extent to which the strength of such land surface feedbacks to precipitation has changed due to changes in land use and land cover change in the SGP. Since the 1950s much of the native vegetation in the region has been replaced by agricultural crops, and this substitution can affect the exchange of water between the surface and the overlying atmosphere. Native plants have much deeper roots and can access soil moisture from reserves unavailable to crops, thereby maintaining the source of moisture for precipitation even during dry spells. Also, crops tend to green up earlier than native plants, so that plant uptake and transpiration of soil moisture begins earlier on agricultural land. The enhanced early season moisture demand could increase drought susceptibility later in the growing season. A further consideration is the widespread adoption of irrigation, which can increase evaporation and transpiration during wet years but is not reliable during exceptional drought years.The research is conducted through a suite of simulations performed using the Weather Research and Forecasting (WRF) model, a regional model which is configured with high resolution over the great plains. WRF is coupled to the Community Land Model (CLM), in which land cover can be specified to represent past and present vegetation cover and varying levels of irrigation can be represented. Experiments consist largely of WRF-CLM simulations over the period of the North American Regional Reanalysis (NARR, 1979-2012), first with land cover held fixed to the modern land cover attributes (from the National Land Cover Database). This simulation is then compared with additional simulations in which land cover is configured to represent conditions during the pre-settlement era (based on data representing the year 1850), intermediate land use conditions around 1920, and the dust bowl. Simulations for modern and intermediate land use are performed with and without irrigation.The work has societal broader impacts due to the economic and societal impact of drought in the SGP. The findings of the research may be useful to the agricultural sector and SGP water managers as they make decisions regarding changes in land and water use in the region. In addition to publications in peer-reviewed research journals, results of the research will be distributed through the University of Nebraska-Lincoln Extension and other extension services across the SGP. In addition the project will support and train two graduate student, thereby providing for the future workforce in this research area.

该项目旨在了解美国南部大平原（SGP）降水变化的原因，大致相当于内布拉斯加州，密苏里州，俄克拉荷马州，阿肯色州，德克萨斯州和路易斯安那州涵盖的地区。 该领域是美国最容易发生干旱的领域之一，具有实质性的经济影响，包括尘埃碗的严重后果以及2011年和2012年的数万美元的损失。该地区的降水异常，包括降雨缺陷，造成干旱的降雨缺陷，通常归因于大规模大气循环的变化，这是由大型大气循环中的变化归因于海面温度（SST温度）。 但是，局部土地表面条件可以通过几种机制来加强远程降水的变化。 例如，缺乏降雨会导致土壤干燥和蒸发减少，从而减少了可用于降水的水分来源，并导致进一步的降雨减少。 同样，由于干旱而导致的温暖的干燥条件在对流层中部促进了山脊，这可以进一步减少降水，因为雨水系统围绕山脊移动。 该项目考虑了由于土地使用变化和SGP的土地覆盖变化，这种土地表面反馈对降水的强度发生了多大程度。 自1950年代以来，该地区的许多天然植被已被农作物取代，这种替代可能会影响地表和上覆的大气之间的水交换。 本地植物具有更深的根源，可以从农作物无法获得的储量中获得土壤水分，从而维持降水的来源，即使在干燥咒语期间也是如此。 同样，农作物倾向于比本地植物早起，因此植物吸收和土壤水分的蒸腾始于农业土地。 增强的早期水分需求可能会在生长期晚些时候提高干旱易感性。 进一步的考虑是灌溉的广泛采用，可以增加潮湿几年的蒸发和蒸腾作用，但在特殊的干旱年份不可靠。该研究是通过使用天气研究和预测（WRF）模型进行的一系列模拟进行的，该模型是一种区域模型，该模型与大平原上的高分辨率配置为大平原。 WRF与社区土地模型（CLM）耦合，其中可以指定土地覆盖代表过去和现在的植被覆盖，并且可以代表不同水平的灌溉水平。 实验主要由WRF-CLM模拟在北美地区重新分析的时期（Narr，1979-2012）组成，首先是固定在现代土地覆盖属性（来自国家土地覆盖数据库）的土地覆盖率。 然后将该仿真与其他模拟进行比较，在该模拟中，将土地覆盖物配置为在预装前时代（基于代表1850年的数据），1920年左右的中间土地使用条件和防尘碗。 对现代和中间土地使用的模拟是在有或没有灌溉的情况下进行的。由于干旱对SGP的经济和社会影响，这项工作对社会具有更广泛的影响。该研究的发现可能对农业部门和SGP水管理人员有用，因为他们就该地区的土地和用水的变化做出决定。 除了经过同行评审的研究期刊的出版物外，该研究的结果还将通过内布拉斯加林肯大学的扩展和其他SGP的其他扩展服务分发。 此外，该项目将支持和培训两名研究生，从而为该研究领域提供未来的劳动力。