Collaborative Research: GPS-based terrestrial water storage anomalies during hydrologic extremes: linking hydrologic process, solid-earth response, and monitoring networks

陆地水储存量（TWS）是以土壤水分、地下水、雪、地表水体和生物圈形式储存的水的总量。TWS的变化反映了流域尺度对干旱和抽取地下水等变化的反应。需要对TWS进行观测以研究水循环及其在地球上的作用，但现有的监测TWS变化的工具并不令人满意。最近，全球定位系统（GPS）观测的陆面高度已被用来量化TWS的变化。然而，从GPS数据估计的TWS的误差还没有被量化。本研究分三个部分来研究如何利用GPS观测来监测TWS。首先，将通过结合水文数据和地球变形模型来量化从GPS地表高度估计的TWS变化的分辨率和准确性。其次，来自数千个站点的GPS数据将用于估计过去十年和未来美国大陆的TWS变化。第三，将在现有的TWS估计和基于GPS观测的估计之间进行比较。该项目的预期成果将通过评估基于GPS的TWS数据的误差幅度和来源，推动TWS监测的起步。这是将这些数据应用于一系列广泛的水文应用的必要步骤，包括土壤水量和地下水补给的估计，干旱的影响，以及地下水储存变化引起的沉降。 TWS异常的观测对于理解水文循环如何响应干旱等强迫是至关重要的。用于监测TWS异常的现有工具对于许多水文应用不是最佳的。最近，GPS观测的地表垂直位移已被用于在新的方式来量化与地下水开采，季节性积雪和干旱TWS异常的空间和时间变化。这些结果表明，基于全球定位系统的位移记录可以大大加强对陆地水循环的监测。然而，迄今为止，没有一项研究量化了从GPS观测估计的TWS异常的误差。该研究计划有三个组成部分，旨在评估如何最好地利用GPS观测来监测TWS。首先，将通过结合水文负荷数据和地球弹性响应模型来量化从GPS垂直位置数据估计的TWS异常的分辨率和精度。其次，来自数千个台站的垂直位置数据将用于估计美国大陆的TWS异常和相关误差，回顾过去十年并及时向前。第三，将在现有的TWS异常产品和基于GPS位置的产品之间进行比较。差异将通过分析地下水、土壤湿度和雪水当量的现场水文观测与水文过程相关。该项目的预期成果将通过评估基于GPS的TWS异常误差与水文过程、固体地球响应和大陆尺度监测网络之间的相互作用的关系，推动TWS监测的起步。这是将这些数据应用于一系列水文应用的必要步骤。

Terrestrial water storage (TWS) is the total amount of water stored as soil moisture, groundwater, snow, in surface water bodies, and in the biosphere. Variations in TWS reflect the watershed-scale response to changes, such as drought and groundwater pumping. Observations of TWS are needed to study the water cycle and its role on the Earth, but existing tools for monitoring TWS variations are not satisfactory. Recently, global positioning system (GPS) observations of the height of the land surface have been used to quantify TWS variations. However, errors in TWS estimated from GPS data have not been quantified. This research has three components to study how GPS observations can be used to monitor TWS. First, the resolution and accuracy of TWS variations estimated from GPS land surface heights will be quantified by combining hydrologic data and a model of how the Earth deforms. Second, GPS data from several thousand stations will be used to estimate TWS variations across the continental United States for the past decade and forward in time. Third, a comparison will be made between existing TWS estimates and estimates based on GPS observations. The expected outcomes of this project will advance the start-of-the-art in TWS monitoring by evaluating the magnitude and sources of errors in GPS-based TWS data. This is a necessary step towards applying these data to a range of wide hydrologic applications, including estimates of soil water volumes and groundwater recharge, the effects of drought, and subsidence caused by changes in groundwater storage. Observations of TWS anomalies are critical for understanding how the hydrologic cycle responds to forcing such as drought. Existing tools for monitoring TWS anomalies are not optimal for many hydrologic applications. Recently, GPS observations of land surface vertical displacement have been used in novel ways to quantify the spatial and temporal variations of TWS anomalies associated with groundwater mining, seasonal snowpack, and drought. These results suggest that GPS-based records of displacement could greatly enhance monitoring of the terrestrial water cycle. However, none of the studies to date have quantified the errors in TWS anomalies estimated from GPS observations. The research plan has three components designed to assess how GPS observations can best be used to monitor TWS. First, the resolution and accuracy of TWS anomalies estimated from GPS vertical position data will be quantified by combining hydrologic loading data and models of the Earth's elastic response. Second, vertical position data from several thousand stations will be used to estimate TWS anomalies and associated errors across the continental United States, retrospectively for the past decade and forward in time. Third, a comparison will be made between existing TWS anomaly products and the product based on GPS positions. Differences will be related to hydrologic processes through analyses of in situ hydrologic observations of groundwater, soil moisture, and snow water equivalent. The expected outcomes of this project will advance the start-of-the-art in TWS monitoring by evaluating how errors in GPS-based TWS anomalies are related to interactions between hydrologic process, the solid earth response, and the monitoring network at the continental scale. This is a necessary step towards applying these data to a range of hydrologic applications.