SGER: The Role of Land-Atmosphere Coupling in Perpetuating Drought

这是气候变率和可预测性计划（CLIVAR）试点项目DRICOMP下的一笔拨款，该项目是干旱耦合模式项目的一部分，重点是对干旱机制进行初步探索，因为它们在全球气候模型的输出中有所体现，并试图评估这些模型在模拟干旱方面的可靠性。该项目的目的是试图了解和确定陆地-大气耦合在气候模式和观测中持续干旱中的作用。由于土壤水分异常具有较大的持续性，强（正）土壤水分-降水耦合的地区将这种持续性传递给降水变率；这将使干旱和潮湿的天气持续下去。在目前的气候模式中，土壤湿度对降水的影响变化很大。这项研究代表了解决几个重要问题的首次探索性努力：与耦合较弱的模式相比，具有强陆地-大气耦合的气候模式是否更有可能出现更长时间和更强烈的干旱？与其他地区相比，具有强陆地-大气耦合的地区是否更有可能遭受持续时间较长的干旱？主要研究人员将分析参与政府间气候变化专门委员会（IPCC）第四次评估报告的气候模型和北美区域气候评估计划（NARCAP）的高分辨率模型数据集。在观测方面，他们将使用北美区域再分析（NARR），一个陆地表面水文循环的回顾性变入渗能力（VIC）模型模拟，来自全球土地数据同化系统（GLDAS）项目的全球数据和来自南部大平原大气辐射测量（ARM）站点的数据。他们将应用滞后相关和回归分析来量化当地土壤湿度和蒸发对后期降水的影响。将定义基于降水、土壤湿度或径流的三个干旱指数。这三个变量在文献中被用作定义“气象”、“农业”和“水文”干旱的基础。对于每个月，地点和数据集，他们将计算整个记录期间每月发生的百分位数。它们将把陆地-大气耦合的强度与干旱的持续时间和强度联系起来。这些研究的更广泛影响在于，它们有助于评估预测未来干旱的气候模型的可靠性。该项目将为研究生提供部分支持。

This is a grant under a Climate Variability and Predictability (CLIVAR) Program pilot project called DRICOMP, for the Drought in Coupled Models Project, which focuses on making initial explorations into the mechanisms of drought as they are represented in the output of global climate models and on attempting to assess the reliability of these models in simulating drought.The objective of this project is to attempt to understand and determine the role of land-atmosphere coupling in perpetuating drought in climate models and in observations. Because soil moisture anomalies have large persistence, regions with strong (positive) soil moisture-precipitation coupling will have this persistence imparted to the precipitation variability; this will act to perpetuate both droughts and wet spells. The effect of soil moisture on precipitation is extremely variable among current climate models.This research represents a first exploratory effort to address several important questions: are climate models with strong land-atmosphere coupling more likely to have longer and more intense droughts than models with weak coupling, are regions of strong land-atmosphere coupling more likely to suffer droughts of long duration compared to other regions, and are climate models with large land-atmosphere coupling more likely to experience longer and more intense droughts in response to climate change?The principal investigators will analyze the climate models participating in the Intergovernmental Panel on Climate Change (IPCC) fourth assessment report and the high-resolution model datasets that are part of the North American Regional Climate Assessment Program (NARCAP). For observations they will use the North American Regional Reanalysis (NARR), a retrospective Variable Infiltration Capacity (VIC) model simulation of the land surface hydrological cycle, global data from the Global Land Data Assimilation Systems (GLDAS) project and data from the Southern Great Plains Atmospheric Radiation Measurement (ARM) site. They will apply lagged correlation and regression analyses to quantify the effect of local soil moisture and evaporation on later precipitation. Three drought indices, based on precipitation, soil moisture or runoff, will be defined. These three variables are used in the literature as the basis for defining "meteorological", "agricultural" and "hydrological" droughts. For each month, location and dataset, they will calculate monthly percentiles of occurrence for the entire period of record. They will relate the strength of land-atmosphere coupling to the duration and intensity of droughts.Broader impacts of the studies are in their contribution to assessing the reliability of climate models in projecting future droughts. The project will provide partial support for a graduate student.