scholarly journals Potential caveats in Land Surface Model evaluations using the U.S. Drought Monitor: roles of base periods and drought indicators

2021 ◽  
Author(s):  
Hailan Wang ◽  
Li Xu ◽  
Mimi Hughes ◽  
Muthuvel Chelliah ◽  
David G DeWitt ◽  
...  
Keyword(s):  
Land Surface ◽  
Land Surface Model ◽  
Water Model ◽  
Drought Indices ◽  
Surface Model ◽  
Short Term ◽  
Sst Variability ◽  
Drought Occurrence ◽  
The U.S

Abstract The U.S. Drought Monitor (USDM) has been widely used as an observational reference for evaluating Land Surface Model (LSM) simulation of drought. This study investigates potential caveats in such evaluation when the USDM and LSMs use different base periods and drought indices to identify drought. The retrospective National Water Model (NWM) v2.0 simulation (1993-2018) was used to exemplify the evaluation, supplemented by North American Land Data Assimilation System Phase 2 (NLDAS-2). In distinct contrast with the USDM which shows high drought occurrence (>50%) in the western half of the continental U.S. (CONUS) and the southeastern U.S. with low occurrence (<30%) elsewhere, the NWM and NLDAS-2 based on soil moisture percentiles (SMPs) consistently show higher drought occurrence (30-40%) in the central and southeastern U.S. than the rest of the CONUS. Much of the differences between the LSMs and USDM, particularly the strong LSM underestimation of drought occurrence in the western and southeastern U.S., are not attributed to the LSM deficiencies, but rather the lack of long-term drought in the LSM simulations due to their relatively short lengths. Specifically, the USDM integrates drought indices with century-long periods of record, which enables it to capture both short-term (<6 months) drought and long-term (>=6 months) drought, whereas the relatively short retrospective simulations of the LSMs allows them to adequately capture short-term drought but not long-term drought. In addition, the USDM integrates many drought indices whereas the NWM results are solely based on the SMP, further adding to the inconsistency. The high occurrence of long-term drought in the western and southeastern U.S. in the USDM is further found to be driven collectively by the post-2000 long-term warm SST trend, cold Pacific Decadal Oscillation (PDO) and warm Atlantic Multi-decadal Oscillation (AMO), all of which are typical leading patterns of global Sea Surface Temperature (SST) variability that can induce drought conditions in the western, central, and southeastern U.S. Our findings highlight the effects of the above caveats and suggest that LSM evaluation should stay qualitative when the caveats are considerable.

scholarly journals Evaluating the effect of alternative carbon allocation schemes in a land surface model (CLM4.5) on carbon fluxes, pools and turnover in temperate forests

2017 ◽  
Author(s):  
Francesc Montané ◽  
Andrew M. Fox ◽  
Avelino F. Arellano ◽  
Natasha MacBean ◽  
M. Ross Alexander ◽  
...  
Keyword(s):  
Primary Production ◽  
Aboveground Biomass ◽  
Land Surface ◽  
Turnover Rate ◽  
Land Surface Model ◽  
Biomass Accumulation ◽  
Deciduous Forests ◽  
Surface Model ◽  
Allocation Scheme

Abstract. How carbon (C) is allocated to different plant tissues (leaves, stem and roots) determines C residence time and thus remains a central challenge for understanding the global C cycle. We used a diverse set of observations (AmeriFlux eddy covariance tower observations, biomass estimates from tree-ring data, and Leaf Area Index (LAI) measurements) to compare C fluxes, pools, and LAI data with those predicted by a Land Surface Model (LSM), the Community Land Model (CLM4.5). We ran CLM for nine temperate (including evergreen and deciduous) forests in North America between 1980 and 2013 using four different C allocation schemes: i) Dynamic C allocation scheme (named "D-CLM") with one dynamic allometric parameter, which allocates C to the stem and leaves to vary in time as a function of annual Net Primary Production (NPP). ii) An alternative dynamic C allocation scheme (named "D-Litton"), where, similar to (i) C allocation is a dynamic function of annual NPP, but unlike (i) includes two dynamic allometric parameters involving allocation to leaves, stem and coarse roots iii–iv) Two fixed C allocation schemes, one representative of observations in evergreen (named "F-Evergreen") and the other of observations in deciduous forests (named "F-Deciduous"). D-CLM generally overestimated Gross Primary Production (GPP) and ecosystem respiration, and underestimated Net Ecosystem Exchange (NEE). In D-CLM, initial aboveground biomass in 1980 was largely overestimated (between 10527 and 12897 g Cm-2) for deciduous forests, whereas aboveground biomass accumulation through time (between 1980 and 2011) was highly underestimated (between 1222 and 7557 g Cm-2) for both evergreen and deciduous sites due to a lower stem turnover rate in the sites than the one used in the model. D-CLM overestimated LAI in both evergreen and deciduous sites because the leaf C-LAI relationship in the model did not match the observed leaf C-LAI relationship at our sites. Although the four C allocation schemes gave similar results for aggregated C fluxes, they translated to important differences in long-term aboveground biomass accumulation and aboveground NPP. For deciduous forests, D-Litton gave more realistic Cstem/Cleaf ratios and strongly reduced the overestimation of initial aboveground biomass, and aboveground NPP for deciduous forests by D-CLM. We identified key structural and parameterization deficits that need refinement to improve the accuracy of LSMs in the near future. That could be done by addressing some of the current model assumptions about C allocation and the associated parameter uncertainty. Our results highlight the importance of using aboveground biomass data to evaluate and constrain the C allocation scheme in the model, and in particular, the sensitivity to the stem turnover rate. Revising these will be critical to improving long-term C processes in LSMs, and improve their projections of biomass accumulation in forests.

scholarly journals Evaluating the effect of alternative carbon allocation schemes in a land surface model (CLM4.5) on carbon fluxes, pools, and turnover in temperate forests

2017 ◽  
Vol 10 (9) ◽  
pp. 3499-3517 ◽  
Author(s):  
Francesc Montané ◽  
Andrew M. Fox ◽  
Avelino F. Arellano ◽  
Natasha MacBean ◽  
M. Ross Alexander ◽  
...  
Keyword(s):  
Primary Production ◽  
Aboveground Biomass ◽  
Land Surface ◽  
Land Surface Model ◽  
Biomass Accumulation ◽  
Deciduous Forests ◽  
Surface Model ◽  
Allocation Scheme ◽  
Tree Ring Data

Abstract. How carbon (C) is allocated to different plant tissues (leaves, stem, and roots) determines how long C remains in plant biomass and thus remains a central challenge for understanding the global C cycle. We used a diverse set of observations (AmeriFlux eddy covariance tower observations, biomass estimates from tree-ring data, and leaf area index (LAI) measurements) to compare C fluxes, pools, and LAI data with those predicted by a land surface model (LSM), the Community Land Model (CLM4.5). We ran CLM4.5 for nine temperate (including evergreen and deciduous) forests in North America between 1980 and 2013 using four different C allocation schemes: i. dynamic C allocation scheme (named "D-CLM4.5") with one dynamic allometric parameter, which allocates C to the stem and leaves to vary in time as a function of annual net primary production (NPP); ii. an alternative dynamic C allocation scheme (named "D-Litton"), where, similar to (i), C allocation is a dynamic function of annual NPP, but unlike (i) includes two dynamic allometric parameters involving allocation to leaves, stem, and coarse roots; iii.–iv. a fixed C allocation scheme with two variants, one representative of observations in evergreen (named "F-Evergreen") and the other of observations in deciduous forests (named "F-Deciduous"). D-CLM4.5 generally overestimated gross primary production (GPP) and ecosystem respiration, and underestimated net ecosystem exchange (NEE). In D-CLM4.5, initial aboveground biomass in 1980 was largely overestimated (between 10 527 and 12 897 g C m−2) for deciduous forests, whereas aboveground biomass accumulation through time (between 1980 and 2011) was highly underestimated (between 1222 and 7557 g C m−2) for both evergreen and deciduous sites due to a lower stem turnover rate in the sites than the one used in the model. D-CLM4.5 overestimated LAI in both evergreen and deciduous sites because the leaf C–LAI relationship in the model did not match the observed leaf C–LAI relationship at our sites. Although the four C allocation schemes gave similar results for aggregated C fluxes, they translated to important differences in long-term aboveground biomass accumulation and aboveground NPP. For deciduous forests, D-Litton gave more realistic Cstem ∕ Cleaf ratios and strongly reduced the overestimation of initial aboveground biomass and aboveground NPP for deciduous forests by D-CLM4.5. We identified key structural and parameterization deficits that need refinement to improve the accuracy of LSMs in the near future. These include changing how C is allocated in fixed and dynamic schemes based on data from current forest syntheses and different parameterization of allocation schemes for different forest types. Our results highlight the utility of using measurements of aboveground biomass to evaluate and constrain the C allocation scheme in LSMs, and suggest that stem turnover is overestimated by CLM4.5 for these AmeriFlux sites. Understanding the controls of turnover will be critical to improving long-term C processes in LSMs.

scholarly journals The AquiFR hydrometeorological modelling platform as a tool for improving groundwater resource monitoring over France: evaluation over a 60-year period

2020 ◽  
Vol 24 (2) ◽  
pp. 633-654 ◽  
Author(s):  
Jean-Pierre Vergnes ◽  
Nicolas Roux ◽  
Florence Habets ◽  
Philippe Ackerer ◽  
Nadia Amraoui ◽  
...  
Keyword(s):  
Resource Management ◽  
Land Surface ◽  
Groundwater Resources ◽  
Land Surface Model ◽  
Groundwater Resource ◽  
Surface Model ◽  
Seasonal Forecasts ◽  
Resource Monitoring ◽  
Aquifer Systems

Abstract. The new AquiFR hydrometeorological modelling platform was developed to provide short-to-long-term forecasts for groundwater resource management in France. This study aims to describe and assess this new tool over a long period of 60 years. This platform gathers in a single numerical tool several hydrogeological models covering much of the French metropolitan area. A total of 11 aquifer systems are simulated through spatially distributed models using either the MARTHE (Modélisation d'Aquifères avec un maillage Rectangulaire, Transport et HydrodynamiquE; Modelling Aquifers with Rectangular cells, Transport and Hydrodynamics) groundwater modelling software programme or the EauDyssée hydrogeological platform. A total of 23 karstic systems are simulated by a lumped reservoir approach using the EROS (Ensemble de Rivières Organisés en Sous-bassins; set of rivers organized in sub-basins) software programme. AquiFR computes the groundwater level, the groundwater–surface-water exchanges and the river flows. A simulation covering a 60-year period from 1958 to 2018 is achieved in order to evaluate the performance of this platform. The 8 km resolution SAFRAN (Système d'Analyse Fournissant des Renseignements Adaptés à la Nivologie) meteorological analysis provides the atmospheric variables needed by the SURFEX (SURFace EXternalisée) land surface model in order to compute surface runoff and groundwater recharge used by the hydrogeological models. The assessment is based on more than 600 piezometers and more than 300 gauging stations corresponding to simulated rivers and outlets of karstic systems. For the simulated piezometric heads, 42 % and 60 % of the absolute biases are lower than 2 and 4 m respectively. The standardized piezometric level index (SPLI) was computed to assess the ability of AquiFR to identify extreme events such as groundwater floods or droughts in the long-term simulation over a set of piezometers used for groundwater resource management. A total of 56 % of the Nash–Sutcliffe efficiency (NSE; Ef) coefficient calculations between the observed and simulated SPLI time series are greater than 0.5. The quality of the results makes it possible to consider using the platform for real-time monitoring and seasonal forecasts of groundwater resources as well as for climate change impact assessments.

Disentangling the long-term foliar 15N signal using a land surface model

2020 ◽  
Author(s):  
Silvia Caldararu ◽  
Tea Thum ◽  
Richard Nair ◽  
Sönke Zaehle
Keyword(s):  
Nutrient Limitation ◽  
Land Surface ◽  
Nitrogen Availability ◽  
Land Surface Model ◽  
Ecosystem Dynamics ◽  
Surface Model ◽  
Terrestrial Vegetation ◽  
Climate System Model ◽  
Foliar N

&lt;p&gt;Terrestrial vegetation growth is hypothesised to increase under elevated atmospheric CO&lt;sub&gt;2&lt;/sub&gt;, a process known as the CO&lt;sub&gt;2&lt;/sub&gt; fertilisation effect. However, the magnitude of this effect and its long-term sustainability remains uncertain. One of the main limitations to the CO2&amp;#160; fertilisation effect is nutrient limitation to plant growth, in particular nitrogen (N) in temperate and boreal ecosystems. Recent studies have suggested that decreases in observed foliar N content (N%) and &amp;#948;&lt;sup&gt;15&lt;/sup&gt;N indicate widespread nitrogen limitation with increasing CO&lt;sub&gt;2&lt;/sub&gt;&amp;#160; concentrations. However, the factors driving these two variables, and especially the foliar &amp;#948;&lt;sup&gt;15&lt;/sup&gt;N values, are complex and can be caused by a number of processes. On one hand, if the observed trends reflect nutrient limitation, this limitation can be caused by either CO&lt;sub&gt;2&lt;/sub&gt; or warming driven growth. On the other hand, it is possible that nutrient limitation does not occur to its full extent due to plant plastic responses to alleviate nutrient limitation, causing a decrease in N%, but changes in the anthropogenic N deposition 15N signal cause the observed &amp;#948;&lt;sup&gt;15&lt;/sup&gt;N trend. In reality, it is likely that all these factors contribute to the observed trends. To understand ecosystem dynamics it is important to disentangle the processes behind these signals which is very difficult based on observational datasets only.&lt;/p&gt;&lt;p&gt;We use a novel land surface model to explore the causes behind the observed trends in foliar N% and &amp;#948;&lt;sup&gt;15&lt;/sup&gt;N. The QUINCY (QUantifying Interactions between terrestrial Nutrient CYcles and the climate system) model&amp;#160; has the unique capacity to track ecologically relevant isotopic composition, including &lt;sup&gt;15&lt;/sup&gt;N in plant and soil pools. The model also includes a realistic representation of plant plastic acclimation processes, specifically a representation of nitrogen allocation to and inside the canopy in response to nitrogen availability, so implicitly to changes in CO&lt;sub&gt;2&amp;#160;&lt;/sub&gt; concentrations. We test the different hypotheses above behind the observed changes in N% and &amp;#948;&lt;sup&gt;15&lt;/sup&gt;N separately and quantify the contribution of each of the factors towards the observed trend. We then test the different hypotheses against existing observations of N% and &amp;#948;&lt;sup&gt;15&lt;/sup&gt;N from the ICP Forests database and other published datasets such as the global dataset of Craine et al. 2018.&lt;/p&gt;&lt;p&gt;Our study showcases the use of an isotope-enabled land surface model in conjunction with long-term observations to strengthen our understanding of the ecosystem processes behind the observed trends.&lt;/p&gt;

scholarly journals CNRD v1.0: a high-quality natural runoff dataset for hydrological and climate studies in China

2021 ◽  
pp. 1-57
Author(s):  
Jiaojiao Gou ◽  
Chiyuan Miao ◽  
Luis Samaniego ◽  
Mu Xiao ◽  
Jingwen Wu ◽  
...  
Keyword(s):  
Parameter Uncertainty ◽  
Land Surface ◽  
Land Surface Model ◽  
Surface Model ◽  
Comprehensive Model ◽  
Analysis Framework ◽  
Model Parameter Uncertainty ◽  
Parameter Uncertainty Analysis ◽  
Climate Studies

Capsule summaryA long-term spatiotemporally continuous naturalized runoff record, CNRD v1.0, is reconstructed by using a comprehensive model parameter uncertainty analysis framework within a land-surface model.

scholarly journals Multisource Estimation of Long-Term Terrestrial Water Budget for Major Global River Basins

2012 ◽  
Vol 25 (9) ◽  
pp. 3191-3206 ◽  
Author(s):  
Ming Pan ◽  
Alok K. Sahoo ◽  
Tara J. Troy ◽  
Raghuveer K. Vinukollu ◽  
Justin Sheffield ◽  
...  
Keyword(s):  
Water Balance ◽  
Error Analysis ◽  
Land Surface ◽  
Water Budget ◽  
Large Scale ◽  
Land Surface Model ◽  
Data Sources ◽  
Surface Model ◽  
Terrestrial Water

A systematic method is proposed to optimally combine estimates of the terrestrial water budget from different data sources and to enforce the water balance constraint using data assimilation techniques. The method is applied to create global long-term records of the terrestrial water budget by merging a number of global datasets including in situ observations, remote sensing retrievals, land surface model simulations, and global reanalyses. The estimation process has three steps. First, a conventional analysis on the errors and biases in different data sources is conducted based on existing validation/error studies and other information such as sensor network density, model physics, and calibration procedures. Then, the data merging process combines different estimates so that biases and errors from different data sources can be compensated to the greatest extent and the merged estimates have the best possible confidence. Finally, water balance errors are resolved using the constrained Kalman filter technique. The procedure is applied to 32 globally distributed major basins for 1984–2006. The authors believe that the resulting global water budget estimates can be used as a baseline dataset for large-scale diagnostic studies, for example, integrated assessment of basin water resources, trend analysis and attribution, and climate change studies. The global scale of the analysis presents significant challenges in carrying out the error analysis for each water budget variable. For some variables (e.g., evapotranspiration) the assumptions underpinning the error analysis lack supporting quantitative analysis and, thus, may not hold for specific locations. Nevertheless, the merging and water balance constraining technique can be applied to many problems.

scholarly journals Global Reach-level 3-hourly River Flood Reanalysis (1980-2019)

2021 ◽  
pp. 1-49
Author(s):  
Yuan Yang ◽  
Ming Pan ◽  
Peirong Lin ◽  
Hylke E. Beck ◽  
Zhenzhong Zeng ◽  
...  
Keyword(s):  
Land Surface ◽  
Land Surface Model ◽  
Surface Model ◽  
Flood Events ◽  
Spatial And Temporal Scales ◽  
Level 3 ◽  
Global Coverage ◽  
River Modeling ◽  
Global Reach

AbstractBetter understanding and quantification of river floods for very local and flashy events calls for modeling capability at fine spatial and temporal scales. However, long-term discharge records with a global coverage suitable for extreme events analysis are still lacking. Here, grounded on recent breakthroughs in global runoff hydrology, river modeling, high resolution hydrography, and climate reanalysis, we developed a 3-hourly river discharge record globally for 2.94 million river reaches during the 40-year period of 1980-2019. The underlying modeling chain consists of the VIC land surface model (0.05°, 3-hourly) that is well calibrated and bias corrected and the RAPID routing model (2.94 million river and catchment vectors), with precipitation input from MSWEP and other meteorological fields downscaled from ERA5. Flood events (above 2-year return) and their characteristics (number, spatial distribution, and seasonality) were extracted and studied. Validations against 3-hourly flow records from 6,000+ gauges in CONUS and daily records from 14,000+ gauges globally show good modeling performance across all flow ranges, good skills in reconstructing flood events (high extremes), and the benefit of (and need for) sub-daily modeling. This data record, referred as Global Reach-level Flood Reanalysis (GRFR), is publicly available at https://www.reachhydro.org/home/records/grfr.

scholarly journals Diagnosing the Nature of Land–Atmosphere Coupling: A Case Study of Dry/Wet Extremes in the U.S. Southern Great Plains

2013 ◽  
Vol 14 (1) ◽  
pp. 3-24 ◽  
Author(s):  
Joseph A. Santanello ◽  
Christa D. Peters-Lidard ◽  
Aaron Kennedy ◽  
Sujay V. Kumar
Keyword(s):  
Great Plains ◽  
Land Surface ◽  
Critical Role ◽  
Land Surface Model ◽  
Coupled System ◽  
Surface Model ◽  
Test Bed ◽  
Southern Great Plains ◽  
Pbl Scheme ◽  
The U.S

Abstract Land–atmosphere (L–A) interactions play a critical role in determining the diurnal evolution of land surface and planetary boundary layer (PBL) temperature and moisture states and fluxes. In turn, these interactions regulate the strength of the connection between surface moisture and precipitation in a coupled system. To address model deficiencies, recent studies have focused on development of diagnostics to quantify the strength and accuracy of the land–PBL coupling at the process level. In this paper, a diagnosis of the nature and impacts of local land–atmosphere coupling (LoCo) during dry and wet extreme conditions is presented using a combination of models and observations during the summers of 2006 and 2007 in the U.S. southern Great Plains. A range of diagnostics exploring the links and feedbacks between soil moisture and precipitation is applied to the dry/wet regimes exhibited in this region, and in the process, a thorough evaluation of nine different land–PBL scheme couplings is conducted under the umbrella of a high-resolution regional modeling test bed. Results show that the sign and magnitude of errors in land surface energy balance components are sensitive to the choice of land surface model, regime type, and running mode. In addition, LoCo diagnostics show that the sensitivity of L–A coupling is stronger toward the land during dry conditions, while the PBL scheme coupling becomes more important during the wet regime. Results also demonstrate how LoCo diagnostics can be applied to any modeling system (e.g., reanalysis products) in the context of their integrated impacts on the process chain connecting the land surface to the PBL and in support of hydrological anomalies.

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