Evaluating interannual water storage changes at watersheds in Illinois based on long‐term soil moisture and groundwater level data

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.

Section: Discussionmentioning

confidence: 99%

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

Greve

Gudmundsson

Orlowsky

et al. 2016

“…Istanbulluoglu et al (2012) and Wang et al (2009) showed interannual storage changes can produce a negative correlation between the evapotranspiration ratio and aridity that is counter to the Budyko curve for baseflowdominated basins in the Nebraska Sand Hills. Wang (2012) evaluated inter-annual storage changes for twelve watersheds in Illinois and showed that, on an annual timescale, variability in runoff and storage is larger than evapotranspiration, and accounting for storage can improve the performance of Budyko predictions. Du et al (2016) presented a method for explicitly accounting for storage changes within the Budyko framework and demonstrated that this approach can greatly improve performance in arid regions, or over shorter timescales where the steady-state assumption is not valid.…”

Section: E Condon and R M Maxwell: Systematic Shifts In Budyko mentioning

confidence: 99%

“…However, with both of these approaches the groundwater system is still not directly simulated or observed. Istanbulluoglu et al (2012) and Wang (2012) did use observations of water table depth to directly quantify storage changes and demonstrate the impact of this change within the Budyko framework; but the study areas with this approach were relatively limited (four watersheds for Istanbulluoglu et al, 2012, andtwelve for Wang, 2012). Groundwater observations sufficient to precisely characterize watershed storage changes are difficult to obtain and are not widely available.…”

Section: E Condon and R M Maxwell: Systematic Shifts In Budyko mentioning

confidence: 99%

Systematic shifts in Budyko relationships caused by groundwater storage changes

Condon

Maxwell

2017

Abstract. Traditional Budyko analysis is predicated on the assumption that the watershed of interest is in dynamic equilibrium over the period of study, and thus surface water partitioning will not be influenced by changes in storage. However, previous work has demonstrated that groundwatersurface water interactions will shift Budyko relationships. While modified Budyko approaches have been proposed to account for storage changes, given the limited ability to quantify groundwater fluxes and storage across spatial scales, additional research is needed to understand the implications of these approximations. This study evaluates the impact of storage changes on Budyko relationships given three common approaches to estimating evapotranspiration fractions: (1) determining evapotranspiration from observations, (2) calculating evapotranspiration from precipitation and surface water outflow, and (3) adjusting precipitation to account for storage changes. We show conceptually that groundwater storage changes will shift the Budyko relationship differently depending on the way evapotranspiration is estimated. A 1-year transient simulation is used to mimic all three approaches within a numerical framework in which groundwater-surface water exchanges are prevalent and can be fully quantified. The model domain spans the majority of the continental US and encompasses 25 000 nested watersheds ranging in size from 100 km 2 to over 3 000 000 km 2 . Model results illustrate that storage changes can generate different spatial patterns in Budyko relationships depending on the approach used. This shows the potential for systematic bias when comparing studies that use different approaches to estimating evapotranspiration. Comparisons between watersheds are also relevant for studies that seek to characterize variability in the Budyko space using other watershed characteristics. Our results demonstrate that within large complex domains the correlation between storage changes and other relevant watershed properties, such as aridity, makes it difficult to easily isolate storage changes as an independent predictor of behavior. However, we suggest that, using the conceptual models presented here, comparative studies could still easily evaluate a range of spatially heterogeneous storage changes by perturbing individual points to better incorporate uncertain storage changes into analysis.

“…Yokoo et al (2008) highlighted the importance of soil water storage change in determining both annual and seasonal water balances. Wang (2012) evaluated changes in inter-annual water storage at 12 watersheds in Illinois using the field observation of long-term groundwater and soil water and found that the impact of inter-annual water storage changes on the water supply in the BH need to be considered. Chen et al (2013) defined the difference between rainfall and storage change as effective precipitation to develop a seasonal model for construction long-term evapotranspiration.…”

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).