Sub-hourly rainfall patterns by hyetograph type under distinct climate conditions in Northeast of Brazil: a comparative inference of their key properties

ABSTRACT The lack of process-based classification procedures may lead to unrealistic hyetograph design due to complex oscillation of rainfall depths when assimilated at high temporal resolutions. Four consecutive years of sub-hourly rainfall data were assimilated in three study areas (Guaraíra, GEB, São João do Cariri, CEB, and Aiuaba, AEB) under distinct climates (very hot semi-arid and tropical wet). This study aimed to define rainfall events (for Minimum Inter-event Time, MIT, and Minimum Rainfall Depth, MRD, equal to 30 min and 1.016 mm, respectively), classify their hyetograph types (rectangular, R, unimodal with left-skewed, UL, right-skewed, UR, and centred peaks, UC, bimodal, B, and shapeless, SL), and compare their key rainfall properties (frequency, duration, depth, rate and peak). A rain pulse aggregation process allowed for reshaping SL-events for six different time spans varying from 2 to 30 min. The results revealed that the coastal area held predominantly R-events (64% events and 49% rainfall depth), in western semi-arid prevailed UL-events (57% events and 63% rainfall depth), whereas in eastern semi-arid mostly were R-events (61% events and 30% rainfall depth) similar to coastal area. It is concluded that each cloud formation type had important effects on hyetograph properties, differentiating them even within the same climate.

摘要
若缺乏基于过程的分类程序，在高时间分辨率下处理降雨数据时，降雨深度会出现复杂振荡，进而导致雨深过程线（hyetograph）的设计脱离实际。本研究针对3个研究区域——瓜赖拉（GEB）、圣若昂-杜卡里里（CEB）、艾乌阿巴（AEB）——采用连续4年的亚小时降雨数据展开分析，这些区域分属极热半干旱与热带湿润两种截然不同的气候类型。
本研究的目标在于：以最小事件间隔时间（Minimum Inter-event Time, MIT）=30分钟、最小降雨深度（Minimum Rainfall Depth, MRD）=1.016毫米为标准界定降雨事件；对其雨深过程线类型进行分类，涵盖矩形（R）、左偏单峰（UL）、右偏单峰（UR）、峰居中单峰（UC）、双峰（B）及无定型（SL）共6类；并对比各类事件的关键降雨特征，包括发生频次、历时、总雨量、降雨强度及峰值。
研究采用降雨脉冲聚合方法，针对2至30分钟共6种不同时间跨度，对无定型（SL）类降雨事件的雨深过程线进行重构。
结果显示：沿海区域以矩形（R）类事件为主，占事件总数的64%，对应降雨量占比49%；西部半干旱区域则以左偏单峰（UL）类事件为主，占事件总数的57%，降雨量占比63%；东部半干旱区域与沿海区域特征相似，同样以矩形（R）类事件为主，占事件总数的61%，对应降雨量占比30%。
研究结论表明，不同云形成类型对雨深过程线特征具有显著影响，即便在同一气候类型下，也能区分出各异的降雨过程线特性。