Scale Dependence in Water Balance Sensitivity to Soil Moisture

水平衡对土壤湿度敏感性的尺度依赖性

• 批准号: 0074045
• 负责人: Guido Salvucci
• 金额: --
• 依托单位: Trustees of Boston University
• 依托单位国家: 美国
• 项目类别: Continuing grant
• 财政年份: 2000
• 资助国家: 美国
• 起止时间: 2000-08-01 至 2004-07-31
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=0074045&HistoricalAwards=false
• 关键词: Scale; Dependence; Water; Balance; Sensitivity

0074045SalvucciMany questions in hydrology have as a common theme the inter-relation of water fluxes and storage at large scales. The issue arises for simple reasons: Transport processes may be reasonably well understood and predictable at small scales, but the scales at which transports become most relevant (either as resources/hazards or with respect to atmosphere interaction) are much larger. At large scales critical parameters (soil, vegetation, and topography) and forcings (radiation, precipitation, wind) are spatially heterogeneous, and transport mechanisms are not only vertical, but lateral (e.g., groundwater redistribution, boundary layer advection). Thus even the simplest question, i.e. "what controls the partitioning of precipitation into evapotranspiration, runoff, drainage and storage change", becomes difficult to answer at large scale. Here we propose a new and simple approach for using direct measurement to address the related question: how does the sensitivity of water balance to soil moisture change with scale?The novelty of the proposed approach is the use of monthly precipitation (P) measurements as a surrogate measure of total outflow from the root zone (evapotranspiration (ET), drainage (D), and runoff (R)). The basis of the method is that the changes in root zone moisture storage (S) over an interval, which make up the difference P-ET-D-R, are themselves uncorrelated with the mean storage over that interval. This lack of correlation is a direct result of the statistical stationary of root zone moisture. The utility of this property is that all of the covariance of ET, D and R with S can be estimated by measuring the covariance of P with S (or by calculating the precipitation rate conditionally averaged at given moisture levels, and taking derivatives). The stationarity condition thus imparts on conditionally averaged precipitation utility as a diagnostic measure of the sensitivity of combined evaporation and drainage/runoff fluxes to soil moisture. Because this simple methodology is based only on mass balance and conditional averaging, it can be applied at any area scale through simple aggregation of P and S data, and thus can be used to directly estimate both the form and the scale-dependence of moisture-water balance sensitivity. As such it can be used to quantify how variability in moisture due to lateral surface and groundwater redistribution processes and land cover/soil/meteorological forcing heterogeneity influence the large-scale sensitivity of water balance to soil moisture.

[74045]水文学中的许多问题都有一个共同的主题，即大尺度上的水通量和储水量之间的相互关系。产生这个问题的原因很简单：在小尺度上，运输过程可能相当容易理解和预测，但运输变得最相关的尺度（无论是作为资源/危害还是相对于大气相互作用）要大得多。在大尺度上，关键参数（土壤、植被和地形）和强迫（辐射、降水、风）在空间上是不均匀的，输送机制不仅是垂直的，而且是横向的（如地下水再分配、边界层平流）。因此，即使是最简单的问题，即。“是什么控制着降水分成蒸散、径流、排水和储存变化”，在大尺度上变得难以回答。在这里，我们提出了一种新的和简单的方法，使用直接测量来解决相关问题：水平衡对土壤湿度的敏感性如何随尺度变化？该方法的新颖之处在于使用月降水量(P)测量作为根区总流出量(蒸散发（ET）、排水（D)和径流(R)）的替代测量。该方法的基础是根区水分储存量（S)在一个区间内的变化(S)弥补了P-ET-D-R的差异）本身与该区间内的平均储存量不相关。这种相关性的缺乏是根区水分统计平稳性的直接结果。这一特性的效用在于，可以通过测量P与S的协方差来估计ET、D和R与S的所有协方差（或通过计算给定湿度水平下的有条件平均降水率并求导）。因此，平稳性条件赋予有条件平均降水效用作为综合蒸发和排水/径流通量对土壤湿度敏感性的诊断度量。由于这种简单的方法仅基于质量平衡和条件平均，因此通过对P和S数据的简单汇总，可以在任何面积尺度上应用，从而可以直接估计水-水平衡敏感性的形式和尺度依赖性。因此，它可以用来量化由于侧向地表和地下水再分配过程和土地覆盖/土壤/气象强迫异质性引起的水分变化如何影响水平衡对土壤水分的大尺度敏感性。