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有显著贡献，但它是中纬度温带地区水文收支中鲜为人知的组成部分。这种不确定性源于其高时空变异性和对复杂的生态生理、水文和陆地-大气界面湍流输送机制相互作用的敏感性。在对流降雨场的描述、对流降雨与地面强迫相互关系的预报和诊断措施方面取得进展。H1)预报：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程控制着夏季对流降水的发生时间和开始时间。H2)诊断性：对流降水活动的后续时空发展虽然与多个尺度的内部气象动力有关，但在一定程度上受陆地表面非均质性的有限尺度控制。这种“指纹”可以通过分析不同土壤湿度前因条件下空间降水和少数陆地表面特征（如地形和土地覆盖指数）的联合概率分布而统计得出。这两个假设是通过利用大气边界层的低维动力模式评估触发对流降雨的陆面过程来解决的。利用空间和小波域互信息分析了对流风暴的时空结构与土壤湿度、地形和土地覆盖的关系。北卡罗莱纳州皮埃蒙特地区之所以被选为案例研究，是因为其频繁的对流降雨模式、夏季水文气候制度、与美国东南部大部分地区在城市和农业土地利用变化趋势上的相似性，以及它作为美国主要林地生产者的经济重要性。智力优势：虽然目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内在不可预测性，但在其物理公式中存在“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和机械方法，但在描述亚网格尺度上的动态重要过程时，如云微物理、复杂湍流波动的闭合模式和陆地表面过程的近似描述，通常面临许多限制。提出的方法将通过提供对对流降水的地表强迫的客观统计特征，并为水文模式和区域气象预测提供基准措施，从而弥合这一基本知识差距。更广泛的影响：建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总体夏季降水的贡献，以评估水资源、干旱风险和林地生存能力。该提案将培养一名研究生，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.