Dominant effect of increasing forest biomass on evapotranspiration: interpretations of movement in Budyko space

Abstract

Abstract. During the last 6 decades, forest biomass has increased in Sweden mainly due to forest management, with a possible increasing effect on evapotranspiration. However, increasing global CO 2 concentrations may also trigger physiological water-saving responses in broadleaf tree species, and to a lesser degree in some needleleaf conifer species, inducing an opposite effect. Additionally, changes in other forest attributes may also affect evapotranspiration. In this study, we aimed to detect the dominating effect(s) of forest change on evapotranspiration by studying changes in the ratio of actual evapotranspiration to precipitation, known as the evaporative ratio, during the period 1961-2012. We first used the Budyko framework of water and energy availability at the basin scale to study the hydroclimatic movements in Budyko space of 65 temperate and boreal basins during this period. We found that movements in Budyko space could not be explained by climatic changes in precipitation and potential evapotranspiration in 60 % of these basins, suggesting the existence of other dominant drivers of hydroclimatic change. In both the temperate and boreal basin groups studied, a negative climatic effect on the evaporative ratio was counteracted by a positive residual effect. The positive residual effect occurred along with increasing standing forest biomass in the temperate and boreal basin groups, increasing forest cover in the temperate basin group and no apparent changes in forest species composition in any group. From the three forest attributes, standing forest biomass was the one that could explain most of the variance of the residual effect in both basin groups. These results further suggest that the water-saving response to increasing CO 2 in these forests is either negligible or overridden by the opposite effect of the increasing forest biomass. Thus, we conclude that increasing standing forest biomass is the dominant driver of long-term and large-scale evapotranspiration changes in Swedish forests.

Quantifying the Impacts of Climate Change and Vegetation Variation on Actual Evapotranspiration Based on the Budyko Hypothesis in North and South Panjiang Basin, China

“…This result indicates that the performance of each Budyko-type equation with a time-varying n t is better than that for a constant n t , which is consistent with the findings of Yang et al [21], Jiang et al [13] and Tian et al [40]. Therefore, compared with the temporally constant parameter n which was used in most previous studies [25,32,33,44,59], the time-varying parameter n improves the accuracy of E a simulation based on the Budyko-type equations and specifically describes the evolution process of E a in the NSPB. [35], Zhang et al [36] and Wang-Tang [37], respectively.…”

“…Generally, the Budyko framework [11] has been widely used to investigate the impacts of climate change and vegetation variations on E a change in various catchments with different climate and land surface conditions because of its conceptual appeal and the fact that it requires only routinely recorded weather data [25,[27][28][29][30][31][32][33]. In addition to the energy and water supplies in the Budyko framework, other factors can influence the process by which water escapes from the land surface into the atmosphere [11,22,28,34], and these factors can be numerically represented by the free parameter, n, in Budyko-type equations [35][36][37].…”

Effects of forest cover change on catchment evapotranspiration variation in China

“…These changes in F (Δ F ) have greatly impacted the terrestrial water cycle (Sterling et al, ; Wei et al, ; Zhou et al, ). In particular, forest changes can substantially influence actual evapotranspiration ( ET ), which in most cases is the second largest term in water balance equations, by changing the physiological features (including leaf stomatal conductance, surface roughness and leaf area index) and biomass of trees (Feng et al, ; Jaramillo et al, ). Thus, quantifying the relationship between F and ET is vital for understanding the effects of forest management on hydrological processes, which will provide important information for land use planning and water resources management.…”

Analysis of the Influence of Rainfall Spatial Uncertainty on Hydrological Simulations Using the Bootstrap Method

“…Vogel and Shallcross [44] used the moving blocks bootstrap to resample the observed time series of stream flow to estimate the storage capacity of a reservoir with different reliability. In order to evaluate the correlation between evapotranspiration and forest biomass, Jaramillo et al [45] performed a bootstrapping procedure to account for the sampling standard errors of the forest attribute data in the regression analysis. In addition, the bootstrap method can also be applied in time series prediction.…”