Ecohydrologic Controls on Convective Rainfall Triggering and Space-Time Development

虽然夏季对流降水对生长季总降雨量贡献很大，但它是中纬度温带地区水文收支中最不为人所知的组成部分之一。这种不确定性源于其高时空变异性及其对陆地-大气界面复杂的生态生理、水文和湍流传输机制之间相互作用的敏感性。为了在对流降雨场的描述方面取得进展，对流降雨与地表强迫之间的相互关系进行预测和诊断措施。H1）预测：在给定的天气条件下，与土壤/植被特征相关的地表水和能量通量的综合时间历史控制着夏季对流降水的时间和发生。H2）诊断：对流降水活动的后续时空发展，同时与内部气象动态有内在联系。在多个尺度上发生作用，部分是由一组有限的尺度控制的，这些尺度可以从地表异质性中进行指纹识别。这种“指纹”可以通过分析不同土壤湿度先决条件的空间降水和少数地表特征（例如地形和土地覆盖指数）的联合概率分布来统计得出。这两个假设是通过使用大气边界层的低维动力学模型评估触发对流降雨的地表过程来解决的。使用空间和小波域中的互信息测量来分析对流风暴的时空结构与土壤湿度、地形和土地覆盖的关系。选择北卡罗来纳州皮埃蒙特地区作为案例研究是因为其频繁的对流降雨模式、夏季水文气候状况、其城市和农业土地利用变化趋势与美国东南部大部分地区的相似性，以及其作为美国主要林地生产地的经济重要性。 智力优点：虽然当前的随机水文模型通过采用高度复杂的时空随机过程直接解决降雨形成和演变的固有不可预测性，但存在他们的物理配方中存在“缺陷”。另一方面，气象学中使用的对流降水模型主要基于基本和机械方法，但在描述其子网格尺度的动态重要过程时通常面临许多限制，例如云微物理、复杂湍流波动的闭合模型以及地表过程的近似描述。拟议的方法将通过提供对流降水的表面强迫的客观统计特征，并为水文模型和区域气象预测提供基准测量，来弥补这一基本知识差距。更广泛的影响：拟议的工作将诊断土地利用变化对对流降水触发因素的影响及其对夏季总体降水的贡献，以评估水资源、干旱风险和林地生存能力。 该提案将培训一名研究生解决水文学、气象学、生态生理学和信息论之间的交叉问题。

While summertime convective precipitation significantly contributes to the total growing season rainfall, it ranks among the least known components in the hydrologic budget of mid-latitude temperate regions. This uncertainty stems from its high space-time variability and its sensitivity to the interplay between complex eco-physiological, hydrologic, and turbulent transport mechanisms at land-atmosphere interface. To progress on the description of convective rainfall fields, both prognostic and diagnostic measures of the interrelationship between convective rainfall and land-surface forcing.H1) Prognostic: For given synoptic conditions, the integrated time history of surface water and energy fluxes, which is related to soil/vegetation characteristics, controls the timing and onset of summertime convective precipitation.H2) Diagnostic: The subsequent space-time development of convective precipitation activity, while inherently related to the internal meteorological dynamics acting at several scales, is partly controlled by a limited set of scales that can be fingerprinted from land-surface heterogeneity. This 'fingerprinting' can be statistically derived by analyzing the joint probability distributions of spatial precipitation and few land surface characteristics (e.g., topographic and land-cover indices) for different soil moisture antecedent conditions.These two hypotheses are addressed by evaluating the land-surface processes that trigger convective rainfall using low-dimensional dynamical models of the atmospheric boundary layer. The space-time structure of the convective storms is analyzed in relation to soil moisture, topography, and land cover using mutual information measures in both space and wavelet domains. The North Carolina Piedmont area is selected as a case study because of its frequent convective rainfall patterns, its summertime hydro-climatic regime, its resemblance to large parts of the Southeastern U.S. in trends of urban and agricultural land-use change, and its economic importance as the primary timberland producer in the United States.Intellectual Merit: While current stochastic hydrologic models directly address the inherent unpredictability of rainfall formation and evolution by employing highly sophisticated space-time random processes, there exists a 'deficit' in their physical formulation. On the other hand, convective precipitation models used in meteorology are primarily based on fundamental and mechanistic approaches but are routinely confronted with numerous limitations in the description of dynamically important processes at their sub-grid scale such as cloud microphysics, closure models for complex turbulent fluctuations, and approximate description of land-surface processes. The proposed approach will bridge this basic knowledge gap by offering an objective statistical characterization of the surface forcing on convective precipitation and providing benchmark measures for both hydrologic models and regional meteorological predictions.Broader impact: The proposed work will diagnose the impact of land use change on triggers of convective precipitation and its contribution to overall summertime precipitation for assessment of water resources, drought risk, and timberland viability. The proposal will train a graduate student in problems lying at the interface between hydrology, meteorology, eco-physiology, and information theory.