Trends in Land Evapotranspiration over Canada for the Period 1960–2000 Based on In Situ Climate Observations and a Land Surface Model

Abstract

An assessment of annual trends in actual evapotranspiration (AET) and associated meteorological inputs is performed at 101 locations across Canada with available long-term hourly surface climate observations to determine if AET in Canada is increasing in relation to observed increases in air temperature. AET was estimated for the dominant land cover class, with representative soil and leaf area index conditions, within a 50 km ϫ 50 km window around each location for the period 1960-2000. The Ecological Assimilation of Land and Climate Observations (EALCO) land surface model, which simulates coupled carbon, energy, and water cycles, was applied to estimate AET on a half-hourly basis at each location using in situ meteorological measurements and ambient atmospheric CO 2 concentrations. Increases in annual AET, of up to 0.73% yr Ϫ1 , were identified at 81 locations, and decreases, of up to 0.25% yr Ϫ1 , were found at the remaining 20 stations. Statistically significant increasing trends were detected in 35% of the locations with the majority corresponding to Atlantic and Pacific coastal regions. Increasing trends were generally related to increasing temperature and total downwelling surface radiation trends in eastern Canada and increasing temperature, surface radiation, and precipitation trends in western Canada. In sharp contrast to other studies based on simpler AET models, annual AET trends in the prairie climate zone were mixed in terms of increases and decreases with no locations showing statistically significant trends. Future studies focused on scaling AET model estimates to subbasins or basins are required both to account for this spatial variability in soil conditions and to permit water budget closure validation.

Spatial and seasonal variations in evapotranspiration over Canada's landmass

“…All these ensure the importance of robust modeling algorithms and accurate model calibration. The limitations of using simple models for ET estimation as compared to process-based models such as EALCO were analyzed and discussed in Fernandes et al (2007). EALCO is a comprehensive model that includes all the major physical and physiological processes related to ET.…”

“…In a later study, Fernandes et al (2007) simulated Canadawide ET using the Ecological Assimilation of Land and Climate Observations (EALCO) model, land surface parameters derived from remote sensing, and observed long-term (30 yr) meteorological data at 101 stations where hourly surface climate observations are available. EALCO is a comprehensive land surface model that was developed with a focus on cold region processes and calibrated and validated using in situ measurements (e.g., tower fluxes) in Canada.…”

“…1) that are dynamically coupled with each other to simulate the land surface: (i) radiation transfer Wang et al, 2007), (ii) energy balance (Wang et al, 2002a;Zhang et al, 2008), (iii) water dynamics including surface watergroundwater interactions (Wang, 2008(Wang, , 2012Wang et al, 2009a, b), and (iv) carbon and (v) nitrogen biogeochemical cycles (Wang et al, , 2002b. EALCO has been calibrated and validated throughout using tower-flux measurements and watershed-level water budget approach, which were reported in the above literature as well as in Amthor et al (2001), Potter et al (2001), Hanson et al (2004), Grant et al (2005Grant et al ( , 2006, Fernandes et al (2007), Mi et al (2007Mi et al ( , 2009, Li et al (2011), Widlowski et al (2011), and Yang et al (2012. In this study, we report the large-scale characterization of ET by EALCO across Canada's landmass and validation by comparing with other existing studies.…”

A Species-Specific and spatially-Explicit Model for Estimating Vegetation Water Requirements in Desert Riparian Forest Zones

“…Different types of models, including ecological models, hydrological models and land surface models, can also simulate and calculate surface ET. Of the different methods used to estimate ET, physically-based methods are thought to have advantages over empirical approaches (Fernandes et al 2007). However, most physicallybased models generally require complicated input data and parameters that focus on the interactions between different land surface processes; and these models are often developed to explore processes' controlling mechanisms without considering their feasibility and applicability in practical managements situations (Wang and Dickinson 2012).…”

Water yield responses to climate change and variability across the North–South Transect of Eastern China (NSTEC)

“…Due to the interactions between P and ET and their high spatiotemporal variability, WY is highly variable and likely the most uncertain component in water balance (Barontini et al, 2009). Since P can be measured relatively easily, recent hydrologic studies have focused on ET, a flux that is more difficult/costly to quantify at local, regional and global scales (Fernandes et al, 2007;Gao et al, 2007;Jung et al, 2010;Sun et al, 2011;Bing et al, 2012). According to the Clausius-Clapeyron relationship that specific humidity increases approximately exponentially with temperature, the global water cycle is accelerating due to the rising temperatures increase ET rates (Huntington, 2006;Meehl et al, 2007;Zhang et al, 2009).…”