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River water balance accounting to evaluate model adequacy and uncertainty in climate and development scenario assessment

机译：河水平衡会计核算在气候和发展情景评估中评估模型充足性和不确定性

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The climate and development scenarios assessed in the Murray-Darling Basin Sustainable Yields project largely made use of existing river models. Some effort was made to assess the adequacy of the models for the project and to identify major sources of uncertainty, both in the scenarios assumed (external uncertainty) and in the river models used to estimate the resulting hydrological changes (internal uncertainty). The assessment addressed data availability, prior model review and testing, and new analysis. In particular, monthly river water balance terms simulated by the baseline river model (representing past climate and current development) were compared reach by reach with largely independent river water balance accounts. Monthly river water balance accounts were developed for the period 1990-2006 wherever possible, by integrating direct streamflow measurements with diversion records, remote sensing based estimates of wetland/floodplain and irrigation water use, and ungauged inflows estimated by the SIMHYD rainfall-runoff model. Statistical and visual data exploration helped to attribute apparent ungauged gains and losses to these terms, with the remainder consisting of unattributed gains and losses or measurement noise. Water accounts were developed for 14 out of 18 regions at the time of writing. These results indicate that on average, about 75% of inflows, outflows, gains and losses is gauged, and about half of the remaining water balance can be accounted for with additional data and modelling. However, large unattributed losses and noise remain, amounting to about 12% of the water balance on average. Among the largest uncertainties in the river water balance were ungauged losses in the lower part of river systems associated with ungauged distributaries, floodplain and wetland inflows, gauge bypass flows and flow harvesting. Remote sensing provides valuable information on the overall magnitude and spatial distribution of these losses, but not how they translate into monthly losses from the main river channel. Generally a major fraction of total inflows was gauged before entering the section of rivers where diversions, regulation and floodplain and wetland losses occur (though there were exceptions). Exchanges of water between the river and groundwater systems could not be estimated and were therefore not included in accounts. Linked river-groundwater modelling suggested that these exchanges are mostly modest. Some common themes emerged when evaluating the implications for the use of the projected changes in river flow regime. For a given change in river inflows, uncertainty in consequent river flows increased towards the end of the system. River models generally performed well in reproducing medium and high flows, but typically less well in simulating low flows. The necessary use of empirical loss functions in river models contributed to uncertainty. Differences between current or potential diversions (assumed in the baseline model) and historic diversions led to discrepancies with the water accounts, with implications for the interpretation of modelling results. The implications for future water accounting efforts are briefly discussed.
机译：默里 - 达令盆地可持续收益率的气候和发展情景在很大程度上利用了现有的河流模型。有些努力评估项目的模型的充分性，并确定在估计所产生的水文变化（内部不确定性）的情况下的情况（外部不确定性）和河流模型中的情况下的主要不确定性来源。评估讨论了数据可用性，先前的模型审查和测试，以及新分析。特别是，基线河流模型（代表过去的气候和当前发展）模拟的每月河水平衡术语通过覆盖范围与大部分独立的河水平衡账户进行比较。每月河水平衡账户在可能的情况下开发了1990 - 2006年，随时随地，通过将​​直接流射流进行直接记录，遥感的湿地/洪泛区和灌溉用水的估算，以及SIMYD降雨径流模型估算的未吞吐量流入。统计和视觉数据探索有助于将显而易见的未损害增长和损失归因于这些术语，其余部分由未分配的收益和损失或测量噪声组成。在撰写本文时，水账已为18个地区14个。这些结果表明，平均值约75％的流入，流出，收益和损失，以及约一半的剩余水平衡可以占额外的数据和建模。然而，平均水平的大约12％的水平仍然存在大的未分配损失和噪音。河水平衡中最大的不确定性是与未吞并分布，洪泛区和湿地流入相关的河流系统下半部分的损失，规格旁路流动和流量收获。遥感提供了有关这些损失的总体幅度和空间分布的有价值的信息，而且还没有如何转化为主要河流渠道的月损失。通常在进入发生转移，监管和洪泛区和湿地损失的河段之前，衡量总流入的主要分数（虽然存在异常）。无法估计河流和地下水系统之间的水交换，因此不包括在账户中。连接的河流地下水建模表明，这些交易所大多是适度的。在评估利用河流流动制度中预计变化的影响时出现了一些共同的主题。对于河流流入的给定变化，随后的河流流量的不确定性在系统的末端增加。河流模型通常在再现介质和高流量时表现良好，但通常在模拟低流量时较少。河流模型中的实证损失函数必要的使用有助于不确定性。当前或潜在转移（假设在基线模型）之间的差异和历史转移导致水账面的差异，对建模结果的解释有影响。简要讨论了对未来的措施努力的影响。

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