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Vegetation modulates Earth's water, energy and carbon cycles. How its functions might change in the future largely depends on how it copes with droughts.sup.1-4. There is evidence that, in places and times of drought, vegetation shifts water uptake to deeper soil.sup.5-7 and rock.sup.8,9 moisture as well as groundwater.sup.10-12. Here we differentiate and assess plant use of four types of water sources: precipitation in the current month (source 1), past precipitation stored in deeper unsaturated soils and/or rocks (source 2), past precipitation stored in groundwater (source 3, locally recharged) and groundwater from precipitation fallen on uplands via river-groundwater convergence toward lowlands (source 4, remotely recharged). We examine global and seasonal patterns and drivers in plant uptake of the four sources using inverse modelling and isotope-based estimates. We find that (1), globally and annually, 70% of plant transpiration relies on source 1, 18% relies on source 2, only 1% relies on source 3 and 10% relies on source 4; (2) regionally and seasonally, source 1 is only 19% in semi-arid, 32% in Mediterranean and 17% in winter-dry tropics in the driest months; and (3) at landscape scales, source 2, taken up by deep roots in the deep vadose zone, is critical in uplands in dry months, but source 4 is up to 47% in valleys where riparian forests and desert oases are found. Because the four sources originate from different places and times, move at different spatiotemporal scales and respond with different sensitivity to climate and anthropogenic forces, understanding the space and time origins of plant water sources can inform ecosystem management and Earth system models on the critical hydrological pathways linking precipitation to vegetation. Global inverse modelling of plant water acquisition depth and isotope-based plant water use estimates demonstrate globally prevalent use of precipitation from distant sources, and that water-stressed ecosystems are well suited to using past and remote precipitation., Author(s): Gonzalo Miguez-Macho [sup.1] , Ying Fan [sup.2] Author Affiliations: (1) CRETUS, Non-Linear Physics Group, Faculty of Physics, Universidade de Santiago de Compostela, Galicia, Spain (2) Department of Earth and [...]

The increase in the number and quality of numerical moisture tracking tools has greatly improved our understanding of the hydrological cycle in recent years. However, the lack of observations has prevented a direct validation of these tools, and it is common to find large discrepancies among the results produced by them, especially between Eulerian and Lagrangian methodologies. Here, we evaluate two diagnostic tools for moisture tracking, WaterSip and UTrack, using simulations from the Lagrangian model FLEXPART. We assess their performance against the Weather Research and Forecasting (WRF) model with Eulerian Water Vapor Tracers (WRF-WVTs). Assuming WRF-WVTs results as a proxy for reality, we explore the discrepancies between the Eulerian and Lagrangian approaches for five precipitation events associated with atmospheric rivers and propose some physics-based adjustments to the Lagrangian tools. Our findings reveal that UTrack, constrained by evaporation and precipitable water data, has a slightly better agreement with WRF-WVTs than WaterSip, constrained by specific humidity data. As in previous studies, we find a negative bias in the contribution of remote sources, such as tropical ones, and an overestimation of local contributions. Quantitatively, the root-mean-square-error (RMSE) for contributions from selected source regions is 5.55 for WaterSip and 4.64 for UTrack, highlighting UTrack's narrowly superior performance. Implementing our simple and logical corrections leads to a significant improvement in both methodologies, effectively reducing the RMSE by over 50 % and bridging the gap between Eulerian and Lagrangian outcomes. Our results suggest that the major discrepancies between the different methodologies were not rooted in their inherently different nature, but in the obviation of basic physical considerations that may be easily straightened out. [ABSTRACT FROM AUTHOR]

This study characterizes moisture source regions for wintertime precipitation across the Salt‐Verde watershed and Arizona (USA) through use of convection‐permitting numerical experiments. We dynamically downscale three four‐month‐long (i.e., December‐January‐February‐March, or DJFM) winter periods: a representative warm (DJFM 1997–1998), cold (DJFM 1999–2000), and neutral (DJFM 2016–2017) winter, as diagnosed by the mean Sea Surface Temperature (SST) across the El Niño 3.4 region compared to a 1995 to 2019 baseline. We utilize the Weather Research and Forecasting (WRF) model with water vapor tracers (WVTs) to distinguish moisture source contributions to total precipitation across Arizona, as originating from land evapotranspiration, sea evaporation, and external advection. Analysis of our numerical experiments demonstrates that WRF is able to capture the day‐to‐day precipitation events across the complex terrain that is characteristic of the Salt‐Verde watershed, but seasonal accumulated precipitation is consistently overestimated compared to individual station observations. The spatial distribution of wintertime monthly accumulated precipitation across Arizona is well captured by WRF, although the total amount of rainfall is overestimated in some confined areas across the highlands of Arizona. Our convection‐permitting WRF experiments also demonstrate that WVT contributions to total wintertime precipitation are apportioned roughly equally between sea evaporation (contributing 45.6%) across the North America west coast and external advection (contributing 48.1%), with land evapotranspiration playing a minimal role (i.e., the remaining 6.3%). We further conduct single‐domain WRF experiments at non‐convection‐permitting resolution and conclude that local sea evaporation, bounded by 140°W and 100°W, is the primary moisture source region to total wintertime precipitation across the Salt‐Verde watershed and Arizona independent of the remote tropical SST across the El Niño 3.4 region. Plain Language Summary: This study characterizes moisture source regions for wintertime precipitation across the Salt‐Verde watershed and Arizona (USA) through use of numerical simulations with the Weather Research and Forecasting (WRF) model. We select and simulate three contemporary winter periods based on their respective mean Sea Surface Temperature (SST) across the central tropical Pacific Ocean compared to a 1995 to 2019 baseline. We utilize WRF with water vapor tracers (WVTs) to distinguish moisture source contributions to total wintertime precipitation across Arizona, as originating from land evapotranspiration, sea evaporation, and external advection. Our results demonstrate that the spatial distribution of wintertime monthly accumulated precipitation across Arizona is well captured by WRF, but the total amount of rainfall is overestimated in some confined areas across the highlands of Arizona. Our WRF experiments also demonstrate that WVT contributions to total wintertime precipitation are apportioned roughly equally between sea evaporation across the North America west coast and external advection, with land evapotranspiration playing a minimal role. We show that local sea evaporation—defined as between meridians 140°W and 100°W—off the North America west coast is the primary moisture source region to total wintertime precipitation across the Salt‐Verde watershed and Arizona independent of the remote SST across the central tropical Pacific Ocean. Key Points: This study characterizes moisture source regions for wintertime precipitation across the Salt‐Verde watershed and Arizona (USA)Water vapor tracer contributions to total winter rainfall are apportioned roughly equally between sea evaporation and external advectionLocal sea evaporation is the main moisture source to total winter rainfall independent of the Sea Surface Temperature across the central tropical Pacific Ocean [ABSTRACT FROM AUTHOR]

ABSTRACT In Galicia, three venerid bivalves are exploited in the intertidal zone by local fishery guilds: Venerupis corrugata, Ruditapes philippinarum, and Rudilapes decussatus. The precise effects of the duration and [...]