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Title: A soil moisture accounting-procedure with a Richards' equation-based soil texture-dependent parameterization

item MATHIAS, SIMON - University Of Durham
item Skaggs, Todd
item QUINN, SIMON - Amec Environment & Infrastructure
item EGAN, SORCHA - University Of Durham
item FINCH, LUCY - University Of Durham
item OLDHAM, CORINNE - University Of Durham

Submitted to: Water Resources Research
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 11/26/2014
Publication Date: 1/23/2015
Citation: Mathias, S.A., Skaggs, T.H., Quinn, S.A., Egan, S.N., Finch, L.E., Oldham, C.D. 2015. A soil moisture accounting-procedure with a Richards' equation-based soil texture-dependent parameterization. Water Resources Research. 51:506-523.

Interpretive Summary: When rain falls on the Earth’s surface, a fraction of the water percolates deeply through the soil and recharges groundwater, a fraction returns to the atmosphere through evaportranspiration processes, and a fraction flows overland to surface waters. This partitioning of rainfall at the land surface is an important part of the hydrologic cycle which greatly affects water management, planning, and risk assessment. Consequently, a number of methods of varying complexity have been developed to calculate the expected partitioning given some specific landscape properties and future weather scenario. In this work, we developed a new procedure for estimating evapotranspiration and groundwater recharge. The method aims for a middle ground in terms of complexity, being simple enough for routine use yet still capturing the essential features of more complex techniques. This research will help hydrologists and engineers quantify groundwater recharge and develop recommendations and guidelines for sustainable water management.

Technical Abstract: Given a time series of potential evapotranspiration and rainfall data, there are at least two approaches for estimating vertical percolation rates. One approach involves solving Richards' equation (RE) with a plant uptake model. An alternative approach involves applying a simple soil moisture accounting procedure (SMAP) based on a set of conceptual stores and conditional statements. It is often desirable to parameterize distributed vertical percolation models using regional soil texture maps. This can be achieved using pedotransfer functions when applying RE. However, robust soil texture based parameterizations for more simple SMAPs have not previously been available. This article presents a new SMAP designed to emulate the response of a one-dimensional homogenous RE model. Model parameters for 231 different soil textures are obtained by calibrating the SMAP model to 20 year time series from equivalent RE model simulations. The results are then validated by comparing to an additional 13 years of simulated RE model data. The resulting work provides a new simple two parameter (% sand and % silt) SMAP, which provides consistent vertical percolation data as compared to RE based models. Results from the 231 numerical simulations are also found to be qualitatively consistent with intuitive ideas concerning soil texture and soil moisture dynamics. Vertical percolation rates are found to be highest in sandy soils. Sandy soils are found to provide less water for evapotranspiration. Surface runoff is found to be more important in soils with high clay content.