GRACE storage-runoff hystereses reveal the dynamics of regional watersheds

E A Sproles,J S Famiglietti,S G Leibowitz,J T Reager,S D Patil,P J Wigington

doi:10.5194/hess-19-3253-2015

Abstract

Abstract. We characterize how regional watersheds function as simple, dynamic systems through a series of hysteresis loops using measurements from NASA's Gravity Recovery and Climate Experiment (GRACE) satellites. These loops illustrate the temporal relationship between runoff and terrestrial water storage in three regional-scale watersheds (> 150 000 km2) of the Columbia River Basin, USA and Canada. The shape and size of the hysteresis loops are controlled by the climate, topography, and geology of the watershed. The direction of the hystereses for the GRACE signals moves in opposite directions from the isolated groundwater hystereses. The subsurface water (soil moisture and groundwater) hystereses more closely resemble the storage-runoff relationship of a soil matrix. While the physical processes underlying these hystereses are inherently complex, the vertical integration of terrestrial water in the GRACE signal encapsulates the processes that govern the non-linear function of regional-scale watersheds. We use this process-based understanding to test how GRACE data can be applied prognostically to predict seasonal runoff (mean Nash-Sutcliffe Efficiency of 0.91) and monthly runoff during the low flow/high demand month of August (mean Nash-Sutcliffe Efficiency of 0.77) in all three watersheds. The global nature of GRACE data allows this same methodology to be applied in other regional-scale studies, and could be particularly useful in regions with minimal data and in trans-boundary watersheds.

Highlights

At the most fundamental level, watershed processes can be described as the collection, storage, and release of water (Black, 1996; McDonnell et al, 2007)
The hysteresis loops begin at the onset of the wet season in October, with terrestrial water storage anomalies (TWSA) increasing (Figs. 3a, 4a–c) as precipitation is stored as snow and soil moisture
Using one integrated measurement from the Gravity Recovery and Climate Experiment (GRACE) satellites, our results show these same processes at the regional scale in the hysteresis loops of storage (TWSA) and runoff (R)

Summary

Introduction

At the most fundamental level, watershed processes can be described as the collection, storage, and release of water (Black, 1996; McDonnell et al, 2007) The runoff from these processes is governed by threshold mediated relationships across scales that result in storage–runoff hystereses (Spence, 2010). These threshold relationships between storage and runoff (S − R) are not uniform across a watershed, functioning as a series of discontinuous processes in soils and hillslopes that provide an integrated S − R relationship at the watershed scale (Spence, 2010). These conceptual models of hydrologic behaviors help provide a process-based understanding of watersheds as dynamic environmental systems (Aspinall, 2010), and identify connections that advance hydrologic science and hydrologic prediction (Wagener et al, 2007).

Methods

Results

Discussion

Conclusion