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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]

This study explores the impacts of groundwater processes on the simulated land‐surface water balance and hydrometeorology. Observations are compared to multiscale Weather Research and Forecasting (WRF) simulations of three summer seasons: 2012, 2013, and 2014. Results show that a grid spacing of 3 km or smaller is necessary to capture small‐scale river and stream networks and associated shallow water tables, which supplies additional root‐zone water double that of simulations with 9‐km and 27‐km grid spacing and is critical to replenishing the depleted vegetation root zones and leads to 150 mm more evapotranspiration. Including groundwater processes in convection‐permitting models is effective to reduce: (1) 2‐m temperature warm biases from 5–6 to 2–3 °C and (2) the low precipitation bias by half. The additional groundwater supply to active soil flux in convection‐permitting simulations with groundwater for June‐August is nearly translated into the same amount of increased precipitation in the domain investigated. Plain Language Summary: Groundwater plays an important role in land‐atmosphere interactions. This study explores the impacts of groundwater processes on the model simulated land‐surface water balance and hydrometeorology. Observations are compared to multiscale Weather Research and Forecasting model simulations of summer seasons for three years: 2012, 2013, and 2014. Results show that high‐resolution modeling (with a grid spacing of 3 km or smaller) is necessary to capture small‐scale river and stream networks and associated shallow water tables, and supply crop and plant root‐zone water double that of low‐resolution simulations, which is critical to replenishing the depleted vegetation root zones and leads to 150 mm more evapotranspiration. Including groundwater processes in high‐resolution models is effective to reduce: (1) 2‐m temperature warm biases from 5–6 to 2–3 °C and (2) the low precipitation bias by half. The additional groundwater supply to active soil flux in high‐resolution simulations with groundwater for June‐August is nearly translated into the same amount of increased precipitation in the domain investigated. Key Points: Groundwater‐atmosphere nexus heavily depends on model resolution and is accelerated at convection‐permitting scalesConvection‐permitting simulations with groundwater effectively mitigates summer warm and dry biases in central United StatesThe amount of water transported from shallow water tables to plant root zones is nearly identical to the increased amount of precipitation [ABSTRACT FROM AUTHOR]

Continued deforestation in the Amazon forest can alter the subsurface/surface and atmospheric branches of the hydrologic cycle. The sign and magnitude of these changes depend on the complex interactions between the water, energy, and momentum budgets. To understand these changes, we use the weather research and forecasting (WRF) model with improved representation of groundwater dynamics and the added feature of Amazonian moisture tracers. The control simulation uses moderate resolution imaging spectroradiometer (MODIS) based observations of land use, and the deforestation simulations use a "business-as-usual" scenario projected for 2040-2050. Our results show that deforestation leads to changes that are seasonally very different. During the dry season, deforestation results in increased albedo and less available net radiation. This change, together with reduced leaf area, results in decreased evapotranspiration (ET), less atmospheric moisture of Amazonian origin, and an increase in temperature. However, we find no changes in precipitation over the basin. Conversely, during the wet season, surface winds increase significantly due to decreased surface roughness. Vapor transport increases throughout the deforested region and leads to an increase in easterlymoisture export, and significant decrease in precipitation within the deforested regions of Eastern Amazon. Contrary to expectations, the moisture tracers in WRF show no evidence that precipitation decreases are due to recycling or changes in stability. [ABSTRACT FROM AUTHOR]

Manmade reservoirs are important components of the terrestrial water balance. Thus, considering the hydro‐climatic effects of reservoirs is important in water cycle studies at a river basin to global scales; yet, reservoirs are represented poorly in large‐scale hydrological and climate models. Here we present a high‐resolution (5 km) continental‐scale reservoir storage dynamics and release scheme by enhancing existing schemes and adding critical novel parameterizations to improve reservoir storage and release simulations. The new scheme simulates river‐floodplain‐reservoir storages in an integrated manner considering their spatial and temporal variations. A new calibration scheme is also incorporated to better simulate reservoir dynamics considering cascade‐reservoir effects. Further, since no reservoir bathymetry data are available over large domains, we use a state‐of‐the‐art digital elevation model and reservoir extent data to derive reservoir bed elevation. The new scheme is integrated within the river‐floodplain routing scheme of a continental hydrological model LEAF‐Hydro‐Flood. Results from the simulation of ~1,900 reservoirs within the contiguous United States suggest that the model well captures the observed reservoir storage‐release dynamics. Comparison of our results with those from the existing schemes suggest a significant improvement; importantly, the new scheme reduces the excessive and frequent reservoir overfilling and underfilling. Comparison of results with satellite‐based surface water data shows that the model accurately reproduces the large‐scale patterns of reservoir‐floodplain inundation extents. It is expected that the results of this study will inform the incorporation of reservoirs in hyper‐resolution models to improve simulations of terrestrial water storage and flow and examine reservoir‐atmosphere interactions over large domains. Key Points: A high‐resolution continental‐scale model is developed for the integrated simulation of river, floodplain, and reservoir storage dynamicsSimulation of reservoir release is improved using an advanced generic reservoir operation rule and an efficient calibration algorithmFirst results of river‐floodplain‐reservoirs storage dynamics are presented [ABSTRACT FROM AUTHOR]

Utility of perennial bioenergy crops (e.g., switchgrass and miscanthus) offers unique opportunities to transition toward a more sustainable energy pathway due to their reduced carbon footprint, averted competition with food crops, and ability to grow on abandoned and degraded farmlands. Studies that have examined biogeophysical impacts of these crops noted a positive feedback between near-surface cooling and enhanced evapotranspiration ( ET), but also potential unintended consequences of soil moisture and groundwater depletion. To better understand hydrometeorological effects of perennial bioenergy crop expansion, this study conducted high-resolution (2-km grid spacing) simulations with a state-of-the-art atmospheric model (Weather Research and Forecasting system) dynamically coupled to a land surface model. We applied the modeling system over the Southern Plains of the United States during a normal precipitation year (2007) and a drought year (2011). By focusing the deployment of bioenergy cropping systems on marginal and abandoned farmland areas (to reduce the potential conflict with food systems), the research presented here is the first realistic examination of hydrometeorological impacts associated with perennial bioenergy crop expansion. Our results illustrate that the deployment of perennial bioenergy crops leads to widespread cooling (1-2 °C) that is largely driven by an enhanced reflection of shortwave radiation and, secondarily, due to an enhanced ET. Bioenergy crop deployment was shown to reduce the impacts of drought through simultaneous moistening and cooling of the near-surface environment. However, simulated impacts on near-surface cooling and ET were reduced during the drought relative to a normal precipitation year, revealing differential effects based on background environmental conditions. This study serves as a key step toward the assessment of hydroclimatic sustainability associated with perennial bioenergy crop expansion under diverse hydrometeorological conditions by highlighting the driving mechanisms and processes associated with this energy pathway. [ABSTRACT FROM AUTHOR]