A reproducible algorithm and R implementation for classifying ecological flood pulse phases from flood-area time series

<title>Abstract</title> <p>Flood-pulse ecology explains how periodic hydrological expansion and contraction structure river-floodplain ecosystems, but local studies often lack a reproducible way to convert continuous hydrological trajectories into ecological analytical units. This paper presents the Flood Pulse Phase Discrimination Index (FPDI), a transparent workflow for classifying Ecological Flood Pulse Phases (EFPP) from a time series of flood-pulse magnitude. FPDI combines the direction of hydrographic change with annual normalized flood magnitude to distinguish Low Water, Flood Expansion, Flood Build-up, Flood Recession, and Flood Contraction. The workflow is demonstrated for Lake Yardi, Ethiopia, where flood area was derived from Sentinel-2 imagery and classified into EFPP phases using a reproducible R implementation. The resulting phases separated hydrological conditions into interpretable expansion, high-water, recession, and contraction states, and threshold sensitivity analysis showed that the Lake Yardi phase structure was robust across tested parameter ranges. FPDI is not proposed as an alternative to the Flood Pulse Concept. Instead, it is a nested operational method for applying flood-pulse theory to small connected floodplain lakes, oxbow systems, and ecological response studies.</p>