Spatial variation and temporal stability of soil water in a snow‐dominated, mountain catchment

Abstract

Abstract:Soil is a critical intermediary of water flux between precipitation and stream flow. Characterization of soil water content (Â, m 3 m 3 ) may be especially difficult in mountainous, snow-dominated catchments due to highly variable water inputs, topography, soils and vegetation. However, individual sites exhibit similar seasonal dynamics, suggesting that it may be possible to describe spatial variability in terms of temporally stable relationships. Working in a 0Ð36 km 2 headwater catchment, we: (i) described and the spatial variability of  over a 2 year period, (ii) characterized that variability in terms of temporal stability analysis, and (iii) related changes in temporally stable soil water patterns to stream flow generation. Soil water data were collected for 2 years at representative sites and quantified in terms of  and water storage to a depth of 75 cm (S 75 , cm). Both S 75 and  were normally distributed in space on all measurement dates. Spatial variability was high relative to other studies, reflecting catchment heterogeneity. However, the ranking of S 75 values displayed temporal stability for all site locations, seasonally and annually. This stability was attributed to soil texture. Further temporal analysis indicated that estimates of catchment mean and standard deviation of S 75 may be characterized with relatively few measurements. Finally, we used temporal linear regression to define catchment soil water conditions related to stream-flow generation. Static, high S 75 conditions in late winter and early spring indicate that stream-flow response is highly sensitive to inputs, whereas static, low S 75 conditions in late summer and early fall indicate minimum stream-flow sensitivity to water inputs. The fall transition was marked by uniform S d across the catchment. The late spring transition was marked by nonuniform S 75 decreases, with the highest S 75 sites decreasing most. Threshold S 75 values identifying catchment sensitivity to water input were identified.

Improving the representation of hydrologic processes in Earth System Models

“…This has received substantial attention in the land modeling community over the past several decades [Shuttleworth, 1988;Entekhabi and Eagleson, 1989;Pitman et al, 1990;Dolman and Gregory, 1992;Koster and Suarez, 1992], and has been addressed in five main ways: (1) explicit representation of subgrid variability-this can be accomplished by configuring the land model with a finer mesh than the rest of the ESM [Hahmann and Dickinson, 2001], by using multiple tiles to represent subgrid heterogeneity [Koster and Suarez, 1992;Bonan et al, 2002], or by explicitly representing the spatial variability for a subset of processes; e.g., separate stomatal conductance calculations for sunlit and shaded leaves [Wang and Leuning, 1998] or separate energy balance calculations for snow-covered and snow-free surfaces [Takata et al, 2003;; (2) statistical-dynamical models, which parameterize how subgrid variability in model state variables affects grid-average fluxes-for example, as discussed in section A1.1, the Probability Distributed Model [Moore and Clarke, 1981] and TOPMODEL [Beven and Kirkby, 1979] represent the impacts of A key missing link in the current generation of land models is representing how the spatial organization of soil moisture and groundwater [Western et al, 1999;Grant et al, 2004] affects land-atmosphere fluxes [Maxwell and Kollet, 2008b]. In particular, most of the land models reviewed in Table 2 have a simplistic representation of the topographic controls on fine-scale soil moisture heterogeneity and the associated heterogeneity in evapotranspiration.…”

Estimating spatially distributed soil water content at small watershed scales based on decomposition of temporal anomaly and time stability analysis

“…This was because deeper CaCO 3 layers and higher SOC were observed in depressions where soils were usually wetter in most of the year because of the snowmelt runoff in the spring and rainfall runoff in the summer and autumn (van der Kamp et al, 2003). Therefore, the roles of soil and topography were two-fold: On one hand, they were highly correlated with the time-stable patterns and thus the time stability of SWC (Gómez-Plaza et al, 2000;Mohanty and Skaggs, 2001;Grant et al, 2004); on the other hand, soil and topography, interplaying with temporal forcing, triggered local-specific soil water change and destroyed time stability of SWC. Their roles in protecting time stability persisted, but their roles in destroying time stability varied with time.…”

A review of advances in hydropedology for application in South Africa

“…The spatial stability relationship between soil and water contents can to a large extent be explained by the soil's clay content, because clay will retain water longer and would therefore have a higher probability of being wetter at any given time (Vachaud et al, 1985;Grant et al, 2004).…”