Shrubland carbon sink depends upon winter water availability in the warm deserts of North America

Biederman, Joel A.; Scott, Russell L.; Arnone, John A.; Jasoni, Richard L.; Litvak, M. E.; Moreo, Michael T.; Papuga, S. A.; Ponce‐Campos, Guillermo E.; Schreiner-McGraw, Adam; Vivoni, Enrique R.

doi:10.1016/j.agrformet.2017.11.005

Cited by 60 publications

(50 citation statements)

References 88 publications

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“…These results support recent work highlighting the importance of winter precipitation for net carbon balance in the warm desert shrublands of North America (Biederman et al. ). However, more work is needed in our study sites to assess the degree these winter soil moisture recharge events may be influencing vegetation and ecosystem processes.…”

Section: Discussionsupporting

confidence: 92%

“…Indeed, based on the intra-annual distribution of storms, it would be expected that winter recharge of deep soil depths is more important in the Sonoran and Mojave ). These results support recent work highlighting the importance of winter precipitation for net carbon balance in the warm desert shrublands of North America (Biederman et al 2018). However, more work is needed in our study sites to assess the degree these winter soil moisture recharge events may be influencing vegetation and ecosystem processes.…”

Section: Importance Of Deep Wetting Eventssupporting

confidence: 91%

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Soil water dynamics at 15 locations distributed across a desert landscape: insights from a 27‐yr dataset

et al. 2018

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Abstract. Desert ecosystems are primarily limited by water availability. Within a climatic regime, topography, soil characteristics, and vegetation are expected to determine how the combined effects of precipitation, temperature, and evaporative demand of the atmosphere shape the spatial and temporal patterns of water within the soil profile and across a landscape. To forecast how desert landscapes may respond to future climatic conditions, it is imperative to improve our understanding of these ecohydrologic processes. Here, we report on 27 yr of monthly soil volumetric water content (VWC) measurements and associated soils data from a site in the northern Chihuahuan Desert of North America. The dataset includes VWC and soil properties measured to 3 m in depth across 15 locations that encompass a range of Chihuahuan Desert vegetation types. We use this unique dataset (1) to generate insights into general temporal and depth patterns in VWC, (2) to analyze how VWC corresponds to measures of climatic conditions, and (3) to qualitatively evaluate the relative importance of soils, topographic setting, and vegetation type in mediating temporal patterns in VWC. Analyses of this unique dataset emphasize the importance of soil and topographic setting in determining depth and temporal patterns in VWC across time. Results emphasize the episodic nature of deep wetting events in our study system-essentially limited to three large events over the 27-yr record driven primarily by wetter than normal winters. Comparison of soil water dynamics between mesquite shrub coppice dunes and interspace soils suggests the "island of fertility" concept does not extend to soil water. Median VWC was strongly coupled to climatic conditions over surprisingly long windows at most locations (6-18 months), suggesting that soil water at depth is decoupled from short climatic pulses. However, VWC dynamics and VWC-climate relationships varied among locations, depths, and seasons, with unexpected similarities in ecohydrologic dynamics observed among very different vegetation types (e.g., an eroded creosote shrubland and a playa grassland). These results further underscore the importance of ecohydrological investigations in these ecosystems, given forecasts for a warmer and more variable climate in deserts globally.

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Section: Discussionsupporting

confidence: 92%

Section: Importance Of Deep Wetting Eventssupporting

confidence: 91%

Soil water dynamics at 15 locations distributed across a desert landscape: insights from a 27‐yr dataset

et al. 2018

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“…The accuracy of EC ET measurements has been checked by comparing them with ET estimated from watershed water balances (Barr et al, ; Scott, ) or lysimeters (Perez‐Priego et al, ), and these studies generally support the conclusion that EC ET is underestimated. However, comparisons at this site and for other dryland shrubland sites generally show that if there is an underestimation, it is probably less than ~10% (Biederman et al, ; Scott, ). Still, we consider a closure‐adjusted ET as an upper bound ( ET /0.89 or 1.12 ET ) on its uncertainty in the water budget and use 1.0 ET for the lower bound.…”

Section: Datamentioning

confidence: 94%

Critical Zone Water Balance Over 13 Years in a Semiarid Savanna

Scott

Biederman

2019

Water Resources Research

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Quantifying how much and when precipitation (P) becomes runoff (R), evapotranspiration (ET), and drainage from the root zone (D) is key to understanding how climate and land use impact hydrology of the critical zone. We quantify water balance dynamics of a semiarid savanna with a summer/winter rainfall pattern with 13 years of water fluxes and soil moisture. We find multiyear P is partitioned 96% to ET and 7% to R, while D (−3%) is negligible when considering measurement uncertainty. While weather regulates ET over diurnal time scales, soil water inputs control seasonal to annual ET amounts. Seasonal water availability, estimated by soil moisture inputs, is more closely tracked by ET rather than time‐averaged soil moisture or P. Surprisingly, we find significant, episodic carryover of soil moisture from the summer to spring growing season. Abundant late‐summer P can supply ET in the subsequent spring, even after multimonth dry periods. However, over an annual cycle beginning in early summer, nearly all soil moisture is used by ET. Likewise, D beyond the monitored root zone, assisted by downward hydraulic distribution in plant roots, occurs within a season, but this is counteracted by subsequent ET extraction of deep moisture over the year. Thus, negligible long‐term D occurs, though there is considerable uncertainty in estimation of this small flux as the residual of much larger ones. These comprehensive, long‐term measurements support expectations about the overriding importance of ET in the dryland critical zone water balance and reveal an unexpected degree of interseasonal water storage.

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“…Fifth, the gap‐filled 30‐min data were summed to daily values and the energy balance closed by linear regression of turbulent fluxes (latent and sensible heat) and available energy ( R net − G ) forced through the origin (Goulden et al, ; Twine et al, ). Energy balance closure was not performed on sites either being cited as unnecessary (Scott, Hamerlynck, Jenerette, Moran, & Barron‐Gafford, ) or in warm deserts, as this has shown to overestimate evapotranspiration by up to 20%, resulting in mean evapotranspiration greater than precipitation (Biederman et al, ). If the ground heat flux was missing from the dataset, it was estimated as

G = 0.35 * ((), R_{net} e^{0.9 * ln ((), 1 - italicfc)}),

where G is the soil heat flux, R net is the net radiation measured from the flux tower, and fc is the fractional canopy cover (Norman, Kustas, & Humes, ).…”

Section: Methodsmentioning

confidence: 99%

“…Second, data processing to fill gaps involved assumptions, such as the decision to force close the energy balance. Literature on this topic is controversial, with some circumstantial evidence that the imbalance in the energy budget ( R net – G = LE + H ), where R net is net radiation, G is the soil heat flux, LE is latent heat, and H is sensible heat, is related to an underestimation of LE and H (Wilson et al, ), and other analyses show that correcting for this imbalance leads to an overestimation of evapotranspiration (Biederman et al, ). We determined whether or not to close the energy balance based on literature reports that forced closure is especially problematic at warm desert sites (Biederman et al, ; Scott, ).…”

Section: Methodsmentioning

confidence: 99%

Evapotranspiration response to multiyear dry periods in the semiarid western United States

Rungee

Bales

Goulden

2018

Hydrological Processes

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Analysis of measured evapotranspiration shows that subsurface plant‐accessible water storage (PAWS) can sustain evapotranspiration through multiyear dry periods. Measurements at 25 flux tower sites in the semiarid western United States, distributed across five land cover types, show both resistance and vulnerability to multiyear dry periods. Average (±standard deviation) evapotranspiration ranged from 660 ± 230 mm yr−1 (October–September) in evergreen needleleaf forests to 310 ± 200 mm yr−1 in grasslands and shrublands. More than 52% of the annual evapotranspiration in Mediterranean climates is supported on average by seasonal drawdown of subsurface PAWS, versus 29% in monsoon‐influenced climates. Snowmelt replenishes dry‐season PAWS by as much as 20% at sites with significant seasonal snow accumulation but was insignificant at most sites. Evapotranspiration exceeded precipitation in more than half of the observation years at sites below 35°N. Annual evapotranspiration at non‐energy‐limited sites increased with precipitation, reaching a mean wet‐year evapotranspiration of 833 mm for evergreen needleleaf forests, 861 mm for mixed forests, 558 mm for woody savannas, 367 mm for grasslands, and 254 mm for shrublands. Thirteen sites experienced at least one multiyear dry period, when mean precipitation was more than one standard deviation below the historical mean. All vegetation types except evergreen needleleaf forests responded to multiyear dry periods by lowering evapotranspiration and/or significant year‐over‐year depletion of subsurface PAWS. Sites maintained wet‐year evapotranspiration rates for 8–33 months before attenuation, with a corresponding net PAWS drawdown of as much as 334 mm. Net drawdown at many sites continued until the dry period ended, resulting in an overall cumulative withdrawal of as much as 558 mm. Evergreen needleleaf forests maintained high evapotranspiration during multiyear dry periods with no apparent PAWS drawdown; these forests currently avoid drought but may prove vulnerable to longer and warmer dry periods that reduce snowpack storage and accelerate evapotranspiration.

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Shrubland carbon sink depends upon winter water availability in the warm deserts of North America

Cited by 60 publications

References 88 publications

Soil water dynamics at 15 locations distributed across a desert landscape: insights from a 27‐yr dataset

Soil water dynamics at 15 locations distributed across a desert landscape: insights from a 27‐yr dataset

Critical Zone Water Balance Over 13 Years in a Semiarid Savanna

Evapotranspiration response to multiyear dry periods in the semiarid western United States

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