Climate elasticity of evapotranspiration shifts the water balance  of Mediterranean climates during multi-year droughts

Avanzi, Francesco; Rungee, Joseph; Maurer, Tessa; Bales, R. C.; Ma, Qin; Glaser, Steven D.; Conklin, M. H.

doi:10.5194/hess-24-4317-2020

Cited by 52 publications

(99 citation statements)

References 62 publications

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“…The shifts in the partitioning of available water can be related to feedback mechanisms between climatic conditions and catchment characteristics that either exacerbate or mitigate drought (Bales et al, 2018;Teuling et al, 2013;Avanzi et al, 2020). (In this study, "exacerbation" and "mitigation" are used with respect runoff).…”

Section: Identifying Mechanisms Of Water Balance Shiftsmentioning

confidence: 99%

“…We examined four basin characteristics and responses to drought that may relate to observed shifts in the precipitation-runoff relationship. These are mechanisms that have previously been associated with drought-induced shifts in the water balance: 1) amount of available water storage (Avanzi et al, 2020;Rungee et al, 2019;Oroza et al, 2018;Hahm et al, 2019a); 2) timing of water availability, which is related to precipitation phase (Avanzi et al, 2020;Rungee et al, 2019;Berghuijs et al, 2014); 3) catchment aridity, which has been correlated with sensitivity to interannual changes in precipitation and departures from the historic mean precipitation (Berghuijs et al, 2014;Saft et al, 2016;Tian et al, 2020); and 4) high-elevation runoff, related to basin spatial heterogeneity that can serve to mitigate drought (Bales et al, 2018). Since not all of these mechanisms are directly measured across the Sierra, we use proxies to estimate their effects.…”

Section: Identifying Mechanisms Of Water Balance Shiftsmentioning

confidence: 99%

“…season baseflows can offer an approximation of the baseline soil water storage in a basin. Basin aridity may influence overall water available to support vegetation through dry periods (Avanzi et al, 2020;Saft et al, 2016;Tian et al, 2020). The second major factor is the vegetation feedback to reduced water availability.…”

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confidence: 99%

“…The second major factor is the vegetation feedback to reduced water availability. Even in areas with high soil water storage, prolonged and/or severe droughts can deplete subsurface storage, eliciting vegetation stress responses such as stomatal closure (Avanzi et al, 2020;Goulden and Bales, 2019) or, in extreme cases, tree die-offs (Bales et al, 2018). These changes to transpiration demand also influence water allocation between ET and runoff, even after the dry period is over.…”

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confidence: 99%

“…In basins with significant snowfall, temperature also influences precipitation phase and the elevation of the snow line (Zhang et al, 2017). These changes, in turn, influence the timing of available water (Rungee et al, 2019;Avanzi et al, 2020) and the spatial distribution of runoff production in the basin (Avanzi et al, 2020;Bales et al, 2018).…”

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confidence: 99%

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Drivers of drought-induced shifts in the water balance through a Budyko approach

Maurer

Avanzi

Glaser

et al. 2021

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Abstract. An inconsistent statistical relationship between precipitation and runoff has been observed between drought and non-drought periods, with less runoff usually observed during droughts than would be predicted using non-drought relationships. Most studies have examined these shifts using multi-linear regression models, which can identify correlations but are less appropriate for analyzing underlying hydrologic mechanisms. In this analysis, we show how the Budyko framework can be leveraged to quantify the impact of shifts in water allocation during drought using 30 years of data for 14 basins in California. We distinguish ″regime″ shifts, which result from changes in the aridity index along the same Budyko curve, from ″partitioning shifts″, which imply a change in the Budyko parameter ω and thus to the relationship among water-balance components that governs partitioning of available water. Regime shifts are primarily due to measurable climatic changes, making them predictable based on drought conditions. Partitioning shifts are related to nonlinear and indirect catchment feedbacks to drought conditions and are thus harder to predict a priori. We show that regime shifts dominate changes in absolute runoff during droughts, but that gains or losses due to partitioning shifts are still significant. We further discuss how basin characteristics and feedbacks correlate and may influence these shifts, finding that low aridity, high baseflow, a shift from snow to rain, and resilience of high-elevation runoff correlate to an increase in runoff as a fraction of precipitation during droughts. This new application of the Budyko framework can help identify mechanisms influencing catchment response to drought, with implications for water management in arid and drought-prone regions.

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Section: Identifying Mechanisms Of Water Balance Shiftsmentioning

confidence: 99%

Section: Identifying Mechanisms Of Water Balance Shiftsmentioning

confidence: 99%

mentioning

confidence: 99%

mentioning

confidence: 99%

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confidence: 99%

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Drivers of drought-induced shifts in the water balance through a Budyko approach

Maurer

Avanzi

Glaser

et al. 2021

Preprint

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Hydrological shifts threaten water resources

Fowler

Horne

Mccutcheon³

et al. 2022

Preprint

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While droughts are synonymous with lower streamflow, the last 10 years have seen a profusion of examples where drought streamflow was surprisingly low-that is, lower than expected, even given low rainfall. Examples include multi-year droughts in California, USA (Avanzi et al., 2020), Chile (Alvarez-Garreton et al., 2021), China (e.g., Tian et al., 2020 and in the south-west and south-east of Australia (Hughes et al., 2012;Saft et al., 2015). Recently, Peterson et al. (2021) reported that these "shifts" toward lower streamflow can be remarkably persistent, with some watersheds seemingly remaining in a shifted state despite a return to near-average climate conditions. For watersheds remaining in this state, a year of average rainfall today produces less streamflow than it did before the drought (Peterson et al., 2021). Given the potentially global extent of these issues, it is pertinent to consider the policy challenges arising for future water resources planning. A long, slow onset of drier conditions under climate change may induce future amplified shifts which are not accounted for in current water resource projections. Once triggered, the pace of onset of such shifts far exceeds the rapidity of climate change more generally, so climate-change-induced hydrological shifts are a significant threat to water systems over time periods relevant to current operational and planning timescales (10-50 years). Shortcomings of Current Models and MethodsWater resource planners rely on hydrological models to simulate streamflow responses to future climate scenarios. Current modeling techniques produce not only uncertain, but often heavily biased, projections of watershed yield under extended dry conditions. When bias occurs, it is typically toward underestimation of drought risk due to a tendency to downplay hydrologic variability and sensitivity to climatic change (Saft, Peel, Western, Perraud, & Zhang, 2016). Current modeling techniques fail to represent the reported hydrological shifts (Saft, Peel, Western, Perraud, & Zhang, 2016), and a similar failure to anticipate future tipping points could result in "surprise" reductions in actual water availability relative to streamflow projections. These model shortcomings require greater attention from the hydrological community, as well as by scientists and policy makers who create or use hydroclimatic projections. While much attention is given to characterizing climatic uncertainty, hydrological uncertainty is also important and complex (Figure 1). Under climate change, many temperate and sub-tropical regions will likely experience drier conditions and more frequent meteorological droughts (Lehner et al., 2017), and a key aspect of improving future water security is understanding how these changes (characterized by precipitation) might translate into impacts on rivers. These impacts include changes in streamflow (yield) as well as

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Alignment between water inputs and vegetation green‐up reduces next year's runoff efficiency

Newcomb,

Van Kirk,

Godsey

et al. 2024

Hydrological Processes

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In the western United States, water supplies largely originate as snowmelt from forested land. Forests impact the water balance of these headwater streams, yet most predictive runoff models do not explicitly account for changing snow‐vegetation dynamics. Here, we present a case study showing how warmer temperatures and changing forests in the Henrys Fork of the Snake River, a seasonally snow‐covered headwater basin in the Greater Yellowstone Ecosystem, have altered the relationship between April 1st snow water equivalent (SWE) and summer streamflow. Since the onset and recovery of severe drought in the early 2000s, predictive models based on pre‐drought relationships over‐predict summer runoff in all three headwater tributaries of the Henrys Fork, despite minimal changes in precipitation or snow accumulation. Compared with the pre‐drought period, late springs and summers (May–September) are warmer and vegetation is greener with denser forests due to recovery from multiple historical disturbances. Shifts in the alignment of snowmelt and energy availability due to warmer temperatures may reduce runoff efficiency by changing the amount of precipitation that goes to evapotranspiration versus runoff and recharge. To quantify the alignment between snowmelt and energy on a timeframe needed for predictive models, we propose a new metric, the Vegetation‐Water Alignment Index (VWA), to characterize the synchrony of vegetation greenness and snowmelt and rain inputs. New predictive models show that in addition to April 1st SWE, the previous year's VWA and summer reference evapotranspiration are the most significant predictors of runoff in each watershed and provide more predictive power than traditionally used metrics. These results suggest that the timing of snowmelt relative to the start of the growing season affects not only annual partitioning of streamflow, but can also determine the groundwater storage state that dictates runoff efficiency the following spring.

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Climate elasticity of evapotranspiration shifts the water balance of Mediterranean climates during multi-year droughts

Cited by 52 publications

References 62 publications

Drivers of drought-induced shifts in the water balance through a Budyko approach

Drivers of drought-induced shifts in the water balance through a Budyko approach

Hydrological shifts threaten water resources

Alignment between water inputs and vegetation green‐up reduces next year's runoff efficiency

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