A one‐parameter Budyko model for water balance captures emergent behavior in darwinian hydrologic models

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: Regression Analysis Of the Residual Effect And Forest Attribmentioning

confidence: 99%

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

Jaramillo

Cory

Arheimer

et al. 2018

“…The parameter b is the maximum value of Y t . Wang and Tang (2014) demonstrated that Eq. (9) S t is controlled by the assumption that the loss rate of actual evaporation from soil water storage is proportional to the evapotranspiration capacity.…”

Section: A Monthly Water Balance Model: Abcd Modelmentioning

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).

“…It is widely used and well-established within the hydrological community, due both to its simplicity and long history, combining experience from over a century of hydrological research. Budyko (1958Budyko ( , 1974 derived a formulation of the function based on findings of Schreiber (1904) and Ol'Dekop (1911), and several other formulations have also been postulated which are numerically very similar (Schreiber, 1904;Ol'Dekop, 1911;Turc, 1954;Mezentsev, 1955;Pike, 1964;Fu, 1981;Choudhury, 1999;Zhang et al, 2001Zhang et al, , 2004Porporato et al, 2004;Yang et al, 2008;Donohue et al, 2012;Wang and Tang, 2014;. Many of these formulations are empirically derived and only few are analytically determined from simple phenomenological assumptions (Fu, 1981;Milly, 1994;Porporato et al, 2004;Zhang et al, 2004;Yang et al, 2007; S. .…”

Section: Introductionmentioning

confidence: 99%

A two-parameter Budyko function to represent conditions under which evapotranspiration exceeds precipitation

Greve

Gudmundsson

Orlowsky

et al. 2016

Abstract. A comprehensive assessment of the partitioning of precipitation (P ) into evapotranspiration (E) and runoff (Q) is of major importance for a wide range of socio-economic sectors. For climatological averages, the Budyko framework provides a simple first-order relationship to estimate water availability represented by the ratio E / P as a function of the aridity index (E p /P , with E p denoting potential evaporation). However, the Budyko framework is limited to steadystate conditions, being a result of assuming negligible storage change in the land-water balance. Processes leading to changes in the terrestrial water storage at any spatial and/or temporal scale are hence not represented. Here we propose an analytically derived modification of the Budyko framework including a new parameter explicitly representing additional water available to evapotranspiration besides instantaneous precipitation. The modified framework is comprehensively analyzed, showing that the additional parameter leads to a rotation of the original water supply limit. We further evaluate the new formulation in an example application at mean seasonal timescales, showing that the extended framework is able to represent conditions in which monthly to annual evapotranspiration exceeds monthly to annual precipitation.