An analytical method for predicting surface soil moisture from rainfall observations

Abstract

[1] A simple analytical method for estimating surface soil moisture directly from rainfall data is proposed and studied. Soil moisture dynamics are represented by a linear stochastic partial differential equation [Entekhabi and Rodriguez-Iturbe, 1994]. A diagnostic equation is derived from the soil moisture dynamics equation by eliminating the diffusion term. The derived daily soil moisture function is a time-weighted average of previous cumulative rainfall over a given period (e.g., >14 days). The advantage of this method is that information on the initial condition of soil moisture, which is often not available at all times and locations, is not needed. The loss coefficient in the diagnostic equation for soil moisture can be estimated from land surface characteristics and soil properties. The method for determining the averaging window size, the loss coefficient, and the infiltration coefficient are described and demonstrated. The soil moisture data observed during three field experiments, i.e., Monsoon'90, Washita'92, and SGP'97, are compared to the calculated soil moisture. The results indicate that the proposed method is robust and has the potential for useful soil moisture predictions.

Using similarity of soil texture and hydroclimate to enhance soil moisture estimation

“…Here, P i denotes the quantity of rainfall during hour i (day in the original presentation in Pan et al, 2003). The soil depth at which an estimation occurs is given by z.…”

“…Similarity here is defined on the basis of hydroclimatic characteristics, using a classification system developed by Coopersmith et al (2012), as well as edaphic (soil) properties. The proposed new scheme maintains the advantage of the parsimonious soil moisture model of Pan et al (2003) in that it does not require specification of initial soil moisture condition, and also there is no need to recalibrate periodically. The model's simplicity also permits implementation of the model in a manner that can easily be refit with new parameters, where necessary.…”

“…Another similar approach employs specific soil type information (theoretically, publicly available data), but ultimately requires proximal sensors to provide the needed soil moisture estimates (Chico-Santamaria et al, 2009). Pan et al (2003) and Pan (2012) addressed many of the shortcomings of the existing modeling approaches reviewed above by developing what they called a "diagnostic soil moisture equation" (i.e., model) in the form of a partial differential equation representing the lumped water balance of a vertical soil column, and representing the soil moisture at any moment in time as a function of the sum of a temporally decaying sequence of observed past rainfall events. The model has the advantage that initial soil moisture conditions are not required (only antecedent precipitation data), nor must the model be recalibrated periodically.…”

“…The aim of this paper is to present and test an approach that can help overcome the issues of calibration at ungauged locations associated with the Pan et al (2003) soil moisture estimation model. The proposed solution involves calibrating the Pan (2012) diagnostic soil moisture equation (model) at gauged sites and then extrapolating the calibrated model to ungauged sites by invoking similarity.…”

A physically based approach for the estimation of root-zone soil moisture from surface measurements

“…The programme, which started in 2004, has developed a network of ground-based observation stations over sub-Saharan West Africa, and several intensive measurement campaigns (see Redelsperger et al, 2006). In particular, three mesoscale sites were implemented in Benin (Pellarin et al, 2009b), Mali (de Rosnay et al, 2009), and Niger (Pellarin et al, 2009a), providing a large amount of information on soil moisture and many other variables. In the present paper, we focused on the point measurements taken at the sites of Nalohou-Mid and Nalohou-Top in Benin, Agoufou in Mali, and Wankama and Tondikiboro in Niger.…”