Quantification of Drainable Water Storage Volumes in Catchments and in River Networks on Global Scales using the GRACE and/or River Runoff
Quantification of Drainable Water Storage Volumes in Catchments and in River Networks on Global Scales using the GRACE and/or River Runoff
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DOI：
10.5194/hess-2018-38
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发表时间：
2018-03
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通讯作者：
J. Riegger
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作者：
J. Riegger
摘要。了解集水区和河网的储水量对于水资源的管理和在气候变化的背景下对环境水的全面描述至关重要。通过GRACE重力卫星或通过对河流或地下水位变化的地面观测对储水量的变化进行测量，不能确定各自的总储水量，后者可能比质量变化本身大得多。此外，GRACE测量的质量变化包括所有存储隔间，无论它们是水力耦合的，导致河流径流，还是不耦合的，如土壤湿度，孤立的地表水或冰雪。从观测到的径流和GRACE中确定水力时间尺度的可能性首次允许在全球尺度上量化总可排水储存量，即由重力自由排水的体积，包括集水区和河网中的所有耦合储存量。利用GRACE对径流-库容（R-S）关系的研究表明，R-S关系可以表征为水力耦合库容的线性时不变（LTI）系统（Riegger and Tourian, 2014）。因此，一旦观测到的相移直接或通过模型进行调整，就可以确定整个系统的水力时间常数和相应的可排水储存量。然而，尽管在建模方法中已经考虑了观测到的相移，但到目前为止，人们还没有详细了解其物理原因和所携带的信息。观察到的相移的一个可能的原因可能是在河网储存中发现的，到目前为止，这还没有在R-S关系中单独解决。与平行排水的储水（如陆上和地下水流）相反，连续的储水会导致时间延迟或相移。这也许可以解释不同阶段的集水区、河网储水量和总储水量。为了研究这种相位效应，建立了具有不同水力时间常数的集水区和河网级联水库系统，并采用分段解析解进行了数学求解。用综合补给时间序列对该方案进行的试验表明，参数估计与总质量或径流量的偏差都以一种独特的方式再现了集水区τC和河网τR的时间常数，并允许分别量化各自的储水量。将级联蓄水方法应用于亚马逊流域，计算和测量的总质量和河流径流非常吻合（Nash-Sutcliffe为信号> 0.96，残差> 0.72）。GRACE和河流径流之间的信号幅度和相移被很好地再现。计算得到的河网质量与多卫星数据集（GIEMS）的全球淹没范围观测到的洪水面积高度相关（0.96），与确定的洪水量相对应。按照集水区存储的顺序实现河网存储，从而描述和解释了w.r.t.相位和信号幅度的观测结果，并允许对集水区和河网中的存储体积进行区分。由于参数优化与河流径流或GRACE质量偏差的比较结果具有可比性，因此即使对于未测量的集水区，也可以通过补给和GRACE来确定河流径流和储存量。主要是充值数据的质量限制了结果的质量。因此，预计水文气象数据产品的进一步发展将改善河流径流和空间可排水储水量的量化。
Abstract. The knowledge of storage volumes in catchments and in river networks is essential for the management of water resources and for a comprehensive description of the environment water in the context of climate change. Measurements of water storage variations by the GRACE gravity satellite or by ground based observations of river or groundwater level variation do not allow to determine the respective total storage volumes, which could be considerably larger than the mass variations themselves. In addition mass variations measured by GRACE comprise all storage compartments whether they are hydraulically coupled, contributing to river runoff, or uncoupled like soil moisture, isolated surface water or snow and ice. The possibility to determine the hydraulic time scale from observed runoff and GRACE for the first time allows to quantify the total Drainable Storage i.e. the volume freely draining with gravity comprising all coupled storages in the catchment and in the river network on global scales. As investigations of the runoff–storage (R–S) relationship using GRACE have shown, the R–S relationship can be characterized as a Linear Time Invariant (LTI) System for hydraulically coupled storage compartments (Riegger and Tourian, 2014). Thus, the respective hydraulic time constant of the total system and the corresponding Drainable Storage can be determined once the observed phase shift is adapted either directly or by a model. However, even though the observed phase shift is already considered in modelling approaches its physical reason and the information it carries is not understood in detail so far. A possible reason for the observed phase shift might be found in the river network storage, which so far has not been addressed separately in the R–S relationships. Opposite to storages draining in parallel (as for overland and groundwater flow) a sequence of storages leads to a temporal delay or a phase shift. This might explain the different phasing of the catchment, the river network storage and the total water storage. In order to investigate such a phasing effect a system of cascaded storages for the catchment and river network is set up with different hydraulic time constants and is mathematically solved by piecewise analytical solutions. Tests of the scheme with synthetic recharge time series show that the parameter estimation either versus deviations in total mass or runoff reproduces the time constants for both, the catchment τC and the river network τR in a unique way and allows to quantify the respective storage volumes individually. The application of the Cascaded Storage approach to the Amazon catchment leads to very good agreements of calculated and measured total mass and river runoff (Nash–Sutcliffe for signals > 0.96, for residuals > 0.72). The signal amplitudes and the phase shift between GRACE and river runoff are reproduced very well. The calculated river network mass highly (0.96) correlates with the observed Flood area from the Global Inundation Extent from Multi-Satellites data set (GIEMS) and corresponds to the determined Flood volumes. The implementation of a river network storage in sequence to catchment storages thus describes and explains the observations w.r.t. phasing and signal amplitudes and allows a discrimination of the storage volumes in the catchment and the river network. As the parameter optimization either versus river runoff or GRACE mass deviations leads to comparable results, river runoff and storage volumes can be determined from recharge and GRACE even for ungauged catchments. It is mainly the quality of the recharge data used that limits the quality of the results. Thus further developments in hydrometeorological data products are expected to improve the quantification of river runoff and drainable water storage volume from space.