Extreme precipitation has received much attention because of its implications for hazard assessment and risk management. However, accurate precipitation information for extreme precipitation research ...from dense rain gauges is still difficult to obtain in developing countries or mountainous regions. Satellite-based precipitation products (SPPs) with high spatial and temporal resolution offer a new way of supplementing data from gauge-based observations. This study aims to evaluate the precision of six SPPs in detail at multiple temporal and spatial scales and explore their ability to capture the characteristics of extreme precipitation from 2009 to 2014 over a semi-arid to semi-humid climate transition area (Wei River basin) in China. The six products are TRMM 3B42RT, TRMM 3B42V7, PERSIANN, PERSIANN CDR, CMORPH RAW, and CRORPH CRT. China gauge-based daily precipitation analysis (CGDPA) provided by the China Meteorological Administration is used as the benchmark reference data. Various statistical evaluation techniques and extreme precipitation indices are used to evaluate and compare the performance of the selected products. The results show that the post real-time products (TRMM 3B42V7, PERSIANN CDR, and CMORPH CRT) agreed better with the reference data than PERSIANN and CMORPH RAW. On a daily scale, TRMM 3B42V7, PERSIANN CDR, and CMORPH CRT displayed similarly good performance. However, at the monthly or annual scale, TRMM 3B42V7 was superior to the other products. With regard to the spatial distribution of precipitation, the datasets performed better over plains and were disappointing over mountainous areas. Additionally, TRMM 3B42V7 provided higher precision and less spatial uncertainty when monitoring extreme precipitation. This study provides a basis for selecting alternative precipitation data for climate transition basins.
Plants are expected to face increasing water stress under future climate change. Most land surface models, including Noah‐MP, employ an idealized “big‐leaf” concept to regulate water and carbon ...fluxes in response to soil moisture stress through empirical soil hydraulics schemes (SHSs). However, such schemes have been shown to cause significant uncertainties in carbon and water simulations. In this paper, we present a novel plant hydraulics scheme (PHS) for Noah‐MP (hereafter, Noah‐MP‐PHS), which employs a big‐tree rather than big‐leaf concept, wherein the whole‐plant hydraulic strategy is considered, including root‐level soil water acquisition, stem‐level hydraulic conductance and capacitance, and leaf‐level anisohydricity and hydraulic capacitance. Evaluated against plot‐level observations from a mature, mixed hardwood forest at the University of Michigan Biological Station and compared with the default Noah‐MP, Noah‐MP‐PHS better represents plant water stress and improves water and carbon simulations, especially during periods of dry soil conditions. Noah‐MP‐PHS also improves the asymmetrical diel simulation of gross primary production under low soil moisture conditions. Noah‐MP‐PHS is able to reproduce different patterns of transpiration, stem water storage and root water uptake during a 2‐week dry‐down period for two species with contrasting plant hydraulic behaviors, i.e., the “cavitation risk‐averse” red maple and the “cavitation risk‐prone” red oak. Sensitivity experiments with plant hydraulic capacitance show that the stem water storage enables nocturnal plant water recharge, affects plant water use efficiency, and provides an important buffer to relieve xylem hydraulic stress during dry soil conditions.
Plain Language Summary
Plants regulate transpiration dynamically through the stomatal aperture, which, in many cases, is governed by plant water status and hydraulic properties. Plant hydraulics describes the mechanics of water movement through plant vascular systems, which is the culmination of emergent phenotypical hydraulic functional traits at the leaf, stem, and root levels. Such physiological mechanisms are excluded in most land surface models, which typically represent plant water stress through empirical soil hydraulics schemes (SHSs) based on either soil water content or soil water potential. In this study, we present a novel plant hydraulics scheme (PHS) to represent plant water stress and the regulation of stomatal conductance for use in the Noah‐MP land surface model. Our results show Noah‐MP‐PHS performs better in its water and carbon simulations than the default Noah‐MP with traditional SHSs, especially under dry soil conditions. Noah‐MP‐PHS also successfully captures the different plant hydraulic behaviors between the “cavitation risk‐averse” red maple and the “cavitation risk‐prone” red oak. Sensitivity experiments also highlight the vital role played by plant water storage in water and carbon simulations in terms of buffering xylem hydraulic stress during soil moisture dry‐down periods. The incorporation of a holistic, whole‐plant hydraulic strategy, along with hydraulic trait‐based vegetation representation, can serve to improve simulations of carbon and water fluxes, particularly in cases of drought and other related disturbances.
Key Points
Noah‐MP‐PHS improves the water and carbon simulations over the default soil hydraulics schemes, especially under dry soil conditions
Noah‐MP‐PHS captures different plant hydraulic behaviors between the “cavitation risk‐averse” maple and the “cavitation risk‐prone” oak
Plant water storage plays a vital role in water and carbon fluxes and relieves xylem hydraulic stress during soil moisture dry‐down periods
Although there is mounting concern about how high vapor pressure deficit (VPD) and low soil moisture (SM) affect ecosystem productivity, their relative importance is still under debate. Here, we ...comprehensively quantified the relative impacts of these two factors on ecosystem gross primary production (GPP) using observations from a global network of eddy‐covariance towers and two approaches (sensitivity analysis and linear regression model). Both approaches agree that a higher percentage of sites experience GPP reduction from high VPD than from low SM over the growing season. However, the constraint of high VPD and low SM on GPP reduction is tightly linked with climates and plant functional types. Humid and mesic ecosystems including forests and grasslands are dominated by VPD, while the semi‐arid and arid ecosystems including shrublands and savannas are dominated by SM. The varying dominant role of these two factors on GPP is closely related to plant stomatal behavior, as predicted by a stomatal conductance model. Additionally, we highlight the non‐linear impact of SM on GPP during droughts and the possible underestimation of the SM effects for deep‐rooted plants when only using surface‐layer SM. Our results shed light on a better understanding of the impacts of VPD and SM on vegetation productivity, with important implications for modeling the response and feedback of ecosystem dynamics to current and future climates.
Plain Language Summary
Vapor pressure deficit (VPD) has increased over recent decades and is expected to continue to rise in the future with climate change. Projected changes in precipitation and soil moisture (SM) are more uncertain with higher spatial variability and larger projected intermodel spread. Given the global environmental changes underway, it is of paramount importance to independently assess the effects of high VPD and low SM on ecosystem productivity. Here, we assessed the relative impacts of these two factors on ecosystem gross primary production (GPP) using observations from a global network of eddy‐covariance towers. We find that reductions in GPP are more attributable to high VPD rather than low SM, on average. The constraint of these two factors on GPP reduction is tightly linked with climates and plant functional types. We further emphasize the amplified impact of SM on GPP during droughts and the need to consider using deep SM. Overall, our findings provide a more comprehensive and quantitative attribution of the impact of increasing atmospheric dryness and changes in soil water deficit on ecosystem productivity in a changing climate.
Key Points
Reductions in gross primary production (GPP) are more attributable to high vapor pressure deficit (VPD) rather than low soil moisture (SM) across all sites
The constraint of high VPD and low SM on GPP reduction is tightly linked with climates and plant functional types
Our results highlight that the relative and non‐linear impacts of VPD and SM on GPP should be adequately considered
Tropical cyclones are an important cause of forest disturbance, and major storms caused severe structural damage and elevated tree mortality in coastal tropical forests. Model capabilities that can ...be used to understand post‐hurricane forest recovery are still limited. We use a vegetation demography model, the Functionally Assembled Terrestrial Ecosystem Simulator, coupled with the Energy Exascale Earth System Model Land Model (ELM‐FATES) to study the processes and the key factors regulating post‐hurricane forest recovery. We implemented hurricane‐induced forest damage, including defoliation, structural biomass reduction, and tree mortality, performed ensemble model simulations, and used random forest feature importance. For the simulation in the Luquillo Experimental Forest, Puerto Rico, we identified factors controlling the post‐hurricane forest recovery, and quantified the sensitivity of key model parameters to the post‐hurricane forest recovery. The results indicate a tendency for the Bisley forests to shift toward the light demanding plant functional type (PFT) when the pre‐hurricane biomass between the light demanding and shade tolerant PFTs is nearly equal and forests experience hurricane disturbance with mortality >60% for both the two PFTs. Under more realistic conditions where the shade tolerant PFT is initially dominant, mortality >80% is required for a shift toward dominance of the light demanding PFT at Bisley. Hurricane mortality and background mortality are the two major factors regulating post‐hurricane forest recovery in simulations. This research improves understanding of the ELM‐FATES model behavior associated with hurricane disturbance and provides guidance for dynamic vegetation model development in representing hurricane induced forest damage with varied intensities.
Plain Language Summary
To enhance the understanding of forest recovery after hurricanes, we implemented hurricane induced forest damage into the Functionally Assembled Terrestrial Ecosystem Simulator, coupled with the Energy Exascale Earth System Model Land Model (ELM‐FATES). We performed ensemble ELM‐FATES simulations with varied forest damage intensities in the Luquillo Experimental Forest, Puerto Rico, and used the output to identify factors controlling the post‐hurricane forest recovery, which was further evaluated with random forest feature importance (RFFI) that quantifies the sensitivity of the key model parameters to the post‐hurricane forest recovery. The results imply that hurricane mortality and background mortality are the major factors regulating post‐hurricane forest recovery. Changes to the intensity of simulated hurricanes could alter forest composition and structure during recovery, which modifies forest ecological processes and potentially shift the wet forests in Puerto Rico to states with increased vulnerability to tropical cyclones. This research enhances our understanding of the ELM‐FATES model behavior associated with hurricane disturbance and broadens the application of RFFI in quantifying the parameter sensitivity of a dynamic global vegetation model (DGVM). This research addresses the essential role of representing hurricane induced forest damage in DGVMs, an advanced tool for the future studies of tropical forest dynamics.
Key Points
Post‐hurricane forest recovery favors the light demanding type when hurricane mortality rates are equal to or higher than 60% at Bisley
Hurricane mortality and background mortality are the key factors regulating the post‐hurricane forest recovery and biomass composition
ELM‐FATES simulations at a Puerto Rico forest site can represent reasonable GPP and ET seasonality but the flux magnitudes are biased low
We develop a novel framework for rigorously evaluating land surface models (LSMs) against observations by recognizing the asymmetry between verification‐ and falsification‐oriented approaches. The ...former approach cannot completely verify LSMs even though it exhausts every case of consistency between the model predictions and observations, whereas the latter only requires a single case of inconsistency to reveal that there must be something wrong. We argue that it is such an inconsistency that stimulates further development of the models and enhancement of the observations. We therefore propose a falsification‐oriented signature‐based evaluation framework to identify cases of inconsistency between model predictions and observations by extracting signatures based on a set of key assumptions. We apply this framework to evaluate an ensemble of simulations from the Noah‐MP LSM against observations over the continental United States under the three assumptions of water mass conservation, no lateral water flow, and a sufficiently long period of time. Regions showing inconsistencies between the Noah‐MP ensemble simulations and the observations are located in the western mountainous areas, the Yellowstone river basin, the lower Floridan aquifer, the Niobrara river basin at the north tip of the Ogallala aquifer, and the basins downstream of the Balcones fault zones in Texas. These regions coincide with the sites where both advances in theoretical modeling and new observational data (e.g., from the Critical Zone Observatories) have emerged.
Plain Language Summary
We propose a framework for locating regions that require substantial efforts in modeling and observations. The framework is based on the fact that a single case of inconsistency between model predictions and observations always indicates that there must be something wrong. Such an consistency can stimulate and guide further development of models and enhancement of observations. An application over the continental United States shows that the identified regions encompass the areas where both theoretical modeling advancements and observational data from the Critical Zone Observatories have emerged. The results also suggest the need to extend the observatories over the Balcones fault zones in Texas and the Floridan aquifer in Florida.
Key Points
A novel framework of falsification‐oriented signature‐based evaluation is proposed
The framework is demonstrated to reveal the regions of inconsistencies between model predictions and observations
The identified regions coincide with the sites where both theoretical modeling advancements and new observational data (e.g., from the Critical Zone Observatories) have emerged
This study elucidates drought characteristics in China during 1980–2015 using two commonly used meteorological drought indices: standardized precipitation index (SPI) and standardized ...precipitation–evapotranspiration index (SPEI). The results show that SPEI characterizes an overall increase in drought severity, area, and frequency during 1998–2015 compared with those during 1980–97, mainly due to the increasing potential evapotranspiration. By contrast, SPI does not reveal this phenomenon since precipitation does not exhibit a significant change overall. We further identify individual drought events using the three-dimensional (i.e., longitude, latitude, and time) clustering algorithm and apply the severity–area–duration (SAD) method to examine the drought spatiotemporal dynamics. Compared to SPI, SPEI identifies a lower drought frequency but with larger total drought areas overall. Additionally, SPEI identifies a greater number of severe drought events but a smaller number of slight drought events than the SPI. Approximately 30% of SPI-detected drought grids are not identified as drought by SPEI, and 40% of SPEI-detected drought grids are not recognized as drought by SPI. Both indices can roughly capture the major drought events, but SPEI-detected drought events are overall more severe than SPI. From the SAD analysis, SPI tends to identify drought as more severe over small areas within 1 million km² and short durations less than 2 months, whereas SPEI tends to delineate drought as more severe across expansive areas larger than 3 million km² and periods longer than 3 months. Given the fact that potential evapotranspiration increases in a warming climate, this study suggests SPEI may be more suitable than SPI in monitoring droughts under climate change.
•Higher frequency of drought events from June to September over mainland China is identified.•The drought center will shift towards south China with increasing frequency of drought events in south ...China.•Future drought events are projected to have shorter duration, smaller affected area but higher intensity over mainland China.
Understanding drought dynamics spatially and temporally is essential for environmental and socio-economic systems, especially under climate change with expected increasing drought. This study aims to update the knowledge about drought spatiotemporal changes over mainland China in the 21st century by utilizing the latest Coupled Model Intercomparison Project Phase 6 (CMIP6) datasets. Precipitation from the nine CMIP6 models is first bias-corrected using a quantile mapping approach and then used to calculate the 3-month Standardized Precipitation Index (SPI) for the historical period and future three scenarios (SSP1-2.6, SSP2-4.5 and SSP5-8.5). We conduct a clustering algorithm to identify three-dimensional (i.e., latitude, longitude, and time) drought events to access the drought dynamics in both space and time. Results show that the drought events occur more frequently during June to September than the other months for both historical and future periods. The drought frequency is significantly increasing during Sep–Dec in the 21st century (increase by about 8.5%, p-value<0.05). Compared with the historical period, drought centers shift toward south under the future projections, indicating a relatively high drought frequency in south China. Additionally, drought events are projected to have shorter duration, smaller affected area, but higher intensity under all three scenarios. The study contributes to our comprehensive understanding of how future drought characteristics will change due to climate change from the perspective of spatiotemporal dynamics. These results are helpful to drought risk management and provide information for developing drought adaptation strategies.
Land surface phenology (LSP), defined as the plant's growth rhythm retrieved from satellite sensing products, is proven to shift with climate change and affect the carbon cycles of terrestrial ...ecosystems. Global afforested area is largely increasing and consequently affecting local and global climate. However, how and to what extent revegetation affects LSP remains relatively unexplored. Here we investigated the difference in four LSPs (i.e., greenup, maturity, senescence, and dormancy) and the response of LSP to climate between restored and native vegetation on Loess Plateau, China, where a remarkable process of vegetation restoration happened during 1982–2015. Most study regions showed a longer growing season (LOS) over time, specifically, with a slight delay in greenup but a relatively large delay in senescence. We found that air temperature was the dominant factor affecting greenup and maturity, while precipitation mostly controlled the senescence and dormancy in the study area. Under similar climate conditions, the LSP of restored vegetation (i.e., restored forest and grassland) showed a significant difference (p < 0.05) from native ones during 1999–2015. Compared to the native forest, restored forest from cropland and grassland showed a delayed greenup date by 0.3 and 3.6 days (p < 0.05) and an advanced dormancy date of 6.6 and 9.0 days (p < 0.05), respectively. Furthermore, the restored vegetation became less sensitive to air temperature than native vegetation, while the restored forest was more sensitive to precipitation, and its growth was affected by the water limitation to a larger extent in the study area. Our study highlights the necessity of considering land use management and its effect on the LSP change to better understand the effect of afforestation on global climate and carbon cycles.
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•Revegetation affected the land surface phenology (LSP) on Loess Plateau.•Growing season of restored vegetation was shorter than that of native vegetation.•LSP of restored vegetation became less dependent on air temperature.•LSP of restored forest was more sensitive to precipitation than that of native one.
Extreme precipitation indices were defined and analyzed in order to estimate the impacts of global climate change on the water source area of the middle route of South-North Water Transfer Project. ...Researches on the extreme precipitation and the intensity of extreme precipitation events show a general increasing trend while no obvious trend found in the frequency of extreme precipitation events. The Mann-Kendall test results indicate all of the three indices’ time series suffered an abrupt change in the late 20th century and after that, the extreme precipitation becomes more frequent with a larger intensity.
Rice protein (RP) and d-xylose (Xe) glycosylation reaction products were prepared by hydrothermal cooking (HTC)-assisted high hydrostatic pressure (HHP) under different pressures (100–300 MPa). The ...structural and functional properties of RP, RP-XeH (only by HTC treatment), and RP-XeHP (by HTC-assisted HHP treatment) were investigated. The results revealed that the grafting degree and solubility of RP-XeHP increased with increasing pressure. Moreover, the intrinsic fluorescence intensity of RP-XeHP decreased, whereas the sugar fluorescence spectroscopy increased. SDS–PAGE revealed that soluble aggregates were formed by the covalent interactions between glutelin and d-xylose in RP-XeHP, and the amino acids that participate in the reaction mainly include Cys, Tyr, Lys, and Arg. FTIR spectral analysis further revealed that the secondary structure changed. Moderate pressure (100 MPa) strengthened the emulsifying properties of RP-XeHP, whereas high pressure (300 MPa) had a negative effect on the emulsifying properties. Furthermore, RP-XeHP exhibited outstanding antioxidant activity. This study provides new insight into RP glycated by HTC-assisted HHP treatment.
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•Hydrothermal cooking-assisted high hydrostatic pressure was a novel glycation method.•Glycosylated products (RP-XeHP) had high grafting degree and low browning intensity.•Moderate pressure (100 Mpa) strengthened emulsifying properties of RP at pH 6–8.•Stronger pressure (300 MPa) weakened emulsifying of RP.•Glycation can improved solution and antioxidant activity of RP.
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