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的贡献很大，但它在中纬度温带地区的水文收支中是最不为人所知的组成部分之一。这种不确定性源于其高度的时空变异性，以及它对陆地-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。为了在描述对流降水场方面取得进展，对流降水和地面强迫之间相互关系的预报和诊断措施都取得了进展。H1)预测：对于给定的天气条件，与土壤/植被特性有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开始。H2)诊断：随后对流降水活动的时空发展虽然内在地与几个尺度上的内部气象动力学有关，但部分地受一组有限的尺度控制，这些尺度可以从陆地-地表的非均质性中提取指纹。通过分析不同土壤湿度前期条件下空间降水和少量地表特征(例如地形和土地覆盖指数)的联合概率分布，可以在统计上得出这种“指纹”。这两个假设是通过使用大气边界层的低维动力学模式来评估触发对流降雨的陆面过程而提出的。利用空间域和小波域的互信息度量，分析了对流风暴的时空结构与土壤水分、地形和土地覆盖的关系。北卡罗来纳州山前地区之所以被选为案例，是因为其频繁的对流降雨模式、夏季水文气候制度、在城市和农业土地利用变化趋势上与美国东南部大部分地区相似，以及作为美国主要林地生产地的经济重要性。智力优势：虽然当前的随机水文模型通过使用高度复杂的时空随机过程直接解决降雨形成和演变的内在不可预测性，但在物理描述方面存在缺陷。另一方面，气象学中使用的对流降水模式主要基于基本的和机械的方法，但在描述次网格尺度上的动力学重要过程方面经常面临许多限制，例如云微物理、复杂湍流波动的闭合模型和陆地表面过程的近似描述。该方法将通过提供地表强迫对对流降水的客观统计特征，并为水文模型和区域气象预报提供基准措施，弥合这一基本知识差距。广泛影响：拟议工作将诊断土地利用变化对对流降水触发的影响及其对夏季总降水量的贡献，以评估水资源、干旱风险和林地生存能力。该提案将对一名研究生进行水文学、气象学、生态生理学和信息论之间的问题培训。

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.