Comparative analysis of the actual evapotranspiration of Flemish forest and cropland, using the soil water balance model WAVE

Abstract

Abstract. This paper focuses on the quantification of the green – vegetation related – water flux of a forest stand in the temperate lowland of Flanders. The underlying reason of the research was to develop a methodology for assessing the impact of forests on the hydrologic cycle in comparison to agriculture. The approach tested for calculating the water consumption by forests was based on the application of the soil water balance model WAVE. The study involved the collection of data from 14 forest stands, the calibration and validation of the WAVE model, and the comparison of the water use (WU) components - transpiration, soil and interception evaporation - between forest and cropland. For model calibration purposes simulated and measured time series of soil water content at different soil depths, period March 2000–August 2001, were compared. A multiple-site validation was conducted as well. Actual tree transpiration calculated with sap flow measurements in three forest stands gave similar results for two of the three stands of pine (Pinus sylvestris L.), but WAVE overestimated the actual measured transpiration for a stand of poplar (Populus sp.). A useful approach to compare the WU components of forest versus cropland is scenario analysis based on the validated WAVE model. The statistical Profile Analysis method was implemented to explore and analyse the simulated WU time-series. With an average annual rainfall of 819 mm, the results show that forests in Flanders consume more water than agricultural crops. A 30 years average of 491 mm for 10 forests stands versus 398 mm for 10 cropped agricultural fields was derived. The WU components, on yearly basis, also differ between the two land use types (transpiration: 315 mm for forest and 261 mm for agricultural land use; soil evaporation: 47 mm and 131 mm, for forest and cropland, respectively). Forest canopy interception evaporation was estimated at 126 mm, while it was negligible for cropland.

Trends in evapotranspiration and its drivers in Great Britain: 1961 to 2015

“…In order to translate between the quoted figures and the model, it is important to note that some authors present the results as the fraction of the total evaporation and others as the fraction of the total precipitation. For instance, Van den Hoof et al (2013) summarizes work from a range of studies in Europe (Choudhury and DiGirolamo, 1998; Verstraeten et al, 2005; Wilson et al, 2001), which focus on the former and quote values of forest interception to range from 13% to 25% of the total evaporation, while for grasses it is closer to 10%. Meanwhile, Nisbet (2005) summarizes a large body of work by scientists studying interception and transpiration in the UK (Calder, 1990; Calder et al, 2003; Roberts, 1983), and focusses on the percentage of rainfall that is intercepted: about 20% of rainfall for BL trees and 35% for needleleaf.…”

Watershed hydrological modelling in data scarce regions; integrating ecohydrology and regionalization for the southern Caspian Sea basin, Iran

“…Evaluating the given data prior to r-r modelling, a preliminary assessment containing unit conversion (i.e. standardizing m 3 /s to mm/d) and ET A calculation (from ET 0 ) was conducted ( FAO, 1998 ; Allen et al., 1998 ; Heryansyah, 2001 ; Verstraeten et al., 2005 ; Jabbarian Amiri et al., 2016 ).…”

Application of a continuous Rainfall-Runoff model to the basin of Kosynthos river using the hydrological software HEC-HMS

“…However, the evapotranspiration computed by the method mentioned above is the potential evapotranspiration of the reference crop, which is different from the soil cover of the basin considered. The potential evapotranspiration of a specific crop, ET c , is calculated as the product of the potential evapotranspiration of the reference crop, ET o , and the crop coefficient c , as outlined in Equation (13) (Doorenbos and Pruitt, 1977;Allen et al, 1998, in Verstraeten et al, 2005: The cross section of Kosynthos River, where the measurements were performed (Figure 4), was divided into subsections, and the mean flow velocity was measured separately in each subsection using an impeller flow meter. The stream discharge in each subsection results as the product of the mean flow velocity and the cross-sectional area of the subsection.…”