Estimating Evaporation in a Prairie Landscape under Drought Conditions

Abstract

Abstract:Physically-based atmospheric models of evapotranspiration (ET) that consider the Penman combination energy balance and aerodynamic approach have achieved acceptance as useful tools for obtaining estimates of actual ET from land surfaces. These models have been made applicable to the case of non-saturated conditions through either surface resistance formulations (e.g., Penman-Monteith) or by application of the complementary evaporation theory of feedback between the atmosphere and surface moisture states (e.g., Granger-Gray). Their application becomes complicated under conditions of drought, when extremely low soil moisture availability severely restricts ET from the soil and plants. Under such severe conditions, consideration for the surface water balance and interactions with the balance of available energy and aerodynamic principles are important for accurately estimating actual ET. A modelling application is demonstrated using the Cold Regions Hydrological Model (CRHM) platform to examine the estimation of ET under drought conditions. CRHM allows users to assemble hydrological models by linking a suite of modular physically-based algorithms that describe the individual processes. In this case, the models assembled consider infiltration, evaporation, and soil moisture accounting and are applied to a mixed prairie located at Lethbridge, Alberta, Canada under drought conditions during the growing period in 2000 and 2001. Near surface meteorological and ecological observations used as model input and for evaluating model performance were obtained through the Ameriflux network and the Agriculture and Agri-Food Canada (AFC) Lethbridge Research Centre. Results show that consideration for the effective rooting zone depth of the mixed-prairie at the site is important for estimating actual ET using the Penman-Montieth and Granger-Gray models during severe moisture stress. Relative differences in ET estimates provided by the models are discussed in the context of their contrasting theoretical approaches.

Multi-variable evaluation of hydrological model predictions for a headwater basin in the Canadian Rocky Mountains

“…In this diagram, the top layer is called the recharge layer, which obtains inputs from infiltration of ponded surface water, snowmelt or sub-canopy rainfall. Evaporation first extracts water from canopy interception and surface storage and then can withdraw moisture via transpiration from only the recharge layer or from both soil column layers, depending on rooting characteristics, and is restricted to plant available soil moisture (Armstrong et al, 2010). Evaporation does not withdraw soil moisture until canopy interception and surface water storage are depleted.…”

An Economic Assessment of Local Farm Multi-Purpose Surface Water Retention Systems under Future Climate Uncertainty

“…Conservation districts in Manitoba promote sustainable development in working to protect their districts natural resources [39]. The frequently saturated land at Pelly's Lake, MB now provides flood water retention, capturing the spring freshet along with rain runoff, and nutrient retention [17,40,41]. The retained water is released in mid-June to maintain baseflow downstream.…”

“…The four most prevalent crops in the study watershed as of 2011, canola, spring wheat, alfalfa, and barley, were modelled with a crop area of 6697 hectares [40]. On average within the study area, there is some initial spring soil moisture associated with snowmelt, however for the purposes of this model, soil moisture was recharged with precipitation and/or irrigation water.…”

An economic assessment of local farm multi-purpose surface water retention systems in a Canadian Prairie setting

“…The reservoir, which has a storage capacity of 1,290,000 m 3 , allows for rain runoff and spring freshet to be captured each year (Armstrong et al 2010;Pomeroy et al 2011). The surface area of the lake is 1,210,000 m 2 , with the dike installation located at the northeast end (Fig.…”