Persistence and memory timescales in root‐zone soil moisture dynamics

作者：Khaled Ghannam, T. Nakai, Athanasios Paschalis, A. Christopher Oishi, Ayumi Kotani, Yasunori Igarashi, Tomo’omi Kumagai, Gabriel G. Katul · 发表于：Water Resources Research · 年份：2016 · DOI：10.1002/2015wr017983 · 被引用次数：121 · 研究领域：Plant Water Relations and Carbon Dynamics、Soil Moisture and Remote Sensing、Tree-ring climate responses

Abstract The memory timescale that characterizes root‐zone soil moisture remains the dominant measure in seasonal forecasts of land‐climate interactions. This memory is a quasi‐deterministic timescale associated with the losses (e.g., evapotranspiration) from the soil column and is often interpreted as persistence in soil moisture states. Persistence, however, represents a distribution of time periods where soil moisture resides above or below some prescribed threshold and is therefore inherently probabilistic. Using multiple soil moisture data sets collected at high resolution (subhourly) across different biomes and climates, this paper explores the differences, underlying dynamics, and relative importance of memory and persistence timescales in root‐zone soil moisture. A first‐order Markov process, commonly used to interpret soil moisture fluctuations derived from climate simulations, is also used as a reference model. Persistence durations of soil moisture below the plant water‐stress level (chosen as the threshold), and the temporal spectrum of upcrossings and downcrossings of this threshold, are compared to the memory timescale and spectrum of the full time series, respectively. The results indicate that despite the differences between meteorological drivers, the spectrum of threshold‐crossings is similar across sites, and follows a unique relation with that of the full soil moisture series. The distribution of persistence times exhibits an approximate stretched exponent...