Large areas in the tropics and at mid‐latitudes experience pronounced seasonality and inter‐annual variability in rainfall and hence water availability. Despite the importance of these seasonally dry ecosystems (SDEs) for the global carbon cycling and in providing ecosystem services, a unifying ecohydrological framework to interpret the effects of climatic variability on SDEs is still lacking. A synthesis of existing data about plant functional adaptations in SDEs, covering some 400 species, shows that leaf phenological variations, rather than physiological traits, provide the dominant control on plant‐water‐carbon interactions. Motivated by this result, the combined implications of leaf phenology and climatic variability on plant water use strategies are here explored with a minimalist model of the coupled soil water and plant carbon balances. The analyses are extended to five locations with different hydroclimatic forcing, spanning seasonally dry tropical climates (without temperature seasonality) and Mediterranean climates (exhibiting out of phase seasonal patterns of rainfall and temperature). The most beneficial leaf phenology in terms of carbon uptake depends on the climatic regime: evergreen species are favoured by short dry seasons or access to persistent water stores, whereas high inter‐annual variability of rainy season duration favours the coexistence of multiple drought‐deciduous phenological strategies. We conclude that drought‐deciduousness may provide a competitive advantage in face of predicted declines in rainfall totals, while reduced seasonality and access to deep water stores may favour evergreen species. This article has been contributed to by US Government employees and their work is in the public domain in the USA.
Particularly in light of California’s recent multiyear drought, there is a critical need for accurate and timely evapotranspiration (ET) and crop stress information to ensure long-term sustainability of high-value crops. Providing this information requires the development of tools applicable across the continuum from subfield scales to improve water management within individual fields up to watershed and regional scales to assess water resources at county and state levels. High-value perennial crops (vineyards and orchards) are major water users, and growers will need better tools to improve water-use efficiency to remain economically viable and sustainable during periods of prolonged drought. To develop these tools, government, university, and industry partners are evaluating a multiscale remote sensing–based modeling system for application over vineyards. During the 2013–17 growing seasons, the Grape Remote Sensing Atmospheric Profile and Evapotranspiration eXperiment (GRAPEX) project has collected micrometeorological and biophysical data within adjacent pinot noir vineyards in the Central Valley of California. Additionally, each year ground, airborne, and satellite remote sensing data were collected during intensive observation periods (IOPs) representing different vine phenological stages. An overview of the measurements and some initial results regarding the impact of vine canopy architecture on modeling ET and plant stress are presented here. Refinements to the ET modeling system based on GRAPEX are being implemented initially at the field scale for validation and then will be integrated into the regional modeling toolkit for large area assessment.
9 10 For monitoring water use in vineyards, it becomes important to evaluate the evapotranspiration 11 (ET) contributions from the two distinct management zones: the vines and the interrow. Often 12 the interrow is not completely bare soil but contains a cover crop that is senescent during the 13 main growing season (nominally May-August), which in Central California is also the dry 14 season. Drip irrigation systems running during the growing season supply water to the vine plant 15 and re-wet some of the surrounding bare soil. However, most of the interrow cover crop is dry 16 stubble by the end of May. This paper analyzes the utility of the thermal-based Two-Source 17 Energy Balance (TSEB) model for estimating daytime ET using tower-based land surface 18 temperature measurements over two Pinot Noir (Vitis vinifera ) vineyards at different levels of 19 maturity in the Central Valley of California near Lodi, CA. The data were collected as part of 20 the Grape Remote sensing Profile and Evapotranspiration eXperiment (GRAPEX). Local eddy 21 covariance (EC) flux tower measurements are used to evaluate the performance of the TSEB 22 model output of the fluxes and the capability of partitioning the vine and cover crop transpiration 23 (T) from the total ET or T/ET ratio. The results for the 2014-2016 growing seasons indicate that 24 TSEB output of the energy balance components and ET, particularly, over the daytime period 25 yield relative differences with flux tower measurements of less than 15%. However, the TSEB 26 model in comparison with flux partitioning method overestimates T/ET during the winter and 27 spring through bud break, but then underestimates during the growing season. A major factor 28 that appears to affect this temporal behavior in T/ET is the daily LAI used as input to TSEB 29 derived from a remote sensing product. 30 31 Keywords vineyards, remote sensing, two source energy balance model, eddy covariance, 32 evapotranspiration, evaporation, transpiration, land surface temperature 33 Man scrip C c e e d ad Ma c U f e TSEB_E&T_ a . df Click here to ie linked References
Abstract. There is increased interest in the interplay between vegetation conditions and overland flow generation. The literature is unclear on this relationship and there is little quantitative guidance for modeling efforts. Therefore, experimental efforts are needed and these call for a lightweight transportable plot-scale (>10 m2) rainfall simulator that can be deployed quickly and quickly redeployed over various vegetation cover conditions. Accordingly, a variable intensity rainfall simulator and collection system was designed and tested in the laboratory and in the field. The system was tested with three configurations of common pressure washing nozzles producing rainfall intensities of 62, 43, and 32 mm h−1 with uniformity coefficients of 76, 65, and 62, respectively, over a plot of 15.12 m2. Field tests were carried out in on a grassy field with silt-loam soil in Orroli, Sardinia in July and August 2010, and rainfall, soil moisture, and runoff data were collected. The two-term Philip infiltration model was used to find optimal values for the saturated hydraulic conductivity of the soil surface and bulk soil, soil water retention curve slope, and air entry suction head. Optimized hydraulic conductivity values were comparable to both the measured final infiltration rate and literature values for saturated hydraulic conductivity. This inexpensive rainfall simulator can therefore be used to identify field parameters needed for hydrologic modeling.
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