Climate controls how ecosystems size the root zone storage capacity at catchment scale

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.

Section: F Jaramillo Et Al: Dominant Effect Of Increasing Forest Bimentioning

confidence: 99%

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

Jaramillo

Cory

Arheimer

et al. 2018

“…Recently, the BH has been widely used to investigate the interannual variability of precipitation partitioning (Gerrits et al, 2009), separation of runoff trends (H.-Y. Xiong et al, 2015), evapotranspiration change (Savenije, 1997) and water storage change (Istanbulluoglu et al, 2012;Gao et al, 2014). These studies show that hydrological processes have been greatly affected by the climate change and intensive change of land cover owing to human activities.…”

Section: Du Et Al: Role Of Water Balance In An Extended Budyko Hymentioning

confidence: 99%

New interpretation of the role of water balance in an extended Budyko hypothesis in arid regions

Sun

et al. 2016

Abstract. The Budyko hypothesis (BH) is an effective approach to investigating long-term water balance at large basin scale under steady state. The assumption of steady state prevents applications of the BH to basins, which is unclosed, or with significant variations in root zone water storage, i.e., under unsteady state, such as in extremely arid regions. In this study, we choose the Heihe River basin (HRB) in China, an extremely arid inland basin, as the study area. We firstly use a calibrated and then validated monthly water balance model, i.e., the abcd model, to quantitatively determine annual and monthly variations of water balance for the sub-basins and the whole catchment of the HRB, and find that the roles of root zone water storage change and that of inflow from upper sub-basins in monthly water balance are significant. With the recognition of the inflow water from other regions and the root zone water storage change as additional possible water sources to evapotranspiration in unclosed basins, we further define the equivalent precipitation (P e ) to include local precipitation, inflow water and root zone water storage change as the water supply in the Budyko framework. With the newly defined water supply, the Budyko curve can successfully describe the relationship between the evapotranspiration ratio and the aridity index at both annual and monthly timescales, whilst it fails when only the local precipitation being considered. Adding to that, we develop a new Fu-type Budyko equation with two non-dimensional parameters (ω and λ) based on the deviation of Fu's equation. Over the annual timescale, the new Fu-type Budyko equation developed here has more or less identical performance to Fu's original equation for the sub-basins and the whole catchment. However, over the monthly timescale, due to large seasonality of root zone water storage and inflow water, the new Fu-type Budyko equation generally performs better than Fu's original equation. The new Fu-type Budyko equation (ω and λ) developed here enables one to apply the BH to interpret regional water balance over extremely dry environments under unsteady state (e.g., unclosed basins or sub-annual timescales).

“…A potentially effective starting point for the latter is to use observations at the modelling scale to infer information about the functional shapes and to quantify the actual parameters of individual processes at that scale. Examples include the concept of master recession curves (Lamb and Beven, 1997) or the water holding capacity in the unsaturated root zone (S U,max ), which is the core of many hydrological systems as it controls the partitioning of drainage and evaporative fluxes (Gao et al, 2014b;de Boer-Euser et al, 2016;Nijzink et al, 2016b). These system components integrate heterogeneities and quantify actual physical properties present and physical processes active at the observation and modelling scale.…”

Section: Modelling Myths -Or Not?mentioning

confidence: 99%

“…A recent example includes , who identified dominant process controls underlying regional differences in regime and flow duration curves. Similarly, Gao et al (2014b) demonstrated how the model parameter representing the water storage capacity in the unsaturated root zone at the macroscale can be considerably constrained exclusively based on water balance data.…”

Section: Organized Complexity and Catchment Similaritymentioning

confidence: 99%

HESS Opinions: The complementary merits of competing modelling philosophies in hydrology

Hrachowitz

Clark

2017

Self Cite

183

130

Abstract. In hydrology, two somewhat competing philosophies form the basis of most process-based models. At one endpoint of this continuum are detailed, high-resolution descriptions of small-scale processes that are numerically integrated to larger scales (e.g. catchments). At the other endpoint of the continuum are spatially lumped representations of the system that express the hydrological response via, in the extreme case, a single linear transfer function. Many other models, developed starting from these two contrasting endpoints, plot along this continuum with different degrees of spatial resolutions and process complexities. A better understanding of the respective basis as well as the respective shortcomings of different modelling philosophies has the potential to improve our models. In this paper we analyse several frequently communicated beliefs and assumptions to identify, discuss and emphasize the functional similarity of the seemingly competing modelling philosophies. We argue that deficiencies in model applications largely do not depend on the modelling philosophy, although some models may be more suitable for specific applications than others and vice versa, but rather on the way a model is implemented. Based on the premises that any model can be implemented at any desired degree of detail and that any type of model remains to some degree conceptual, we argue that a convergence of modelling strategies may hold some value for advancing the development of hydrological models.