scholarly journals Simulating precipitation decline under a Mediterranean deciduous Oak forest: effects on isoprene seasonal emissions and predictions under climatic scenarios

2017 ◽  
Author(s):  
Anne-Cyrielle Genard-Zielinski ◽  
Christophe Boissard ◽  
Elena Ormeño ◽  
Juliette Lathière ◽  
Ilja M. Reiter ◽  
...  
Keyword(s):  
Water Stress ◽  
Seasonal Variations ◽  
Land Surface ◽  
Environmental Changes ◽  
Seasonal Pattern ◽  
Land Surface Model ◽  
Surface Model ◽  
Emission Rates ◽  
Drought Intensity ◽  
Isoprene Emission

Abstract. Seasonal variations of Q. pubescens physiology and isoprene emission rates (ER) were studied from June 2012 to June 2013 at the O3HP site (French Mediterranean) under natural (ND) and amplified (+30 %, AD) drought. While AD significantly reduced the stomatal conductance to water vapour over the season excepting August, it did not significantly limit CO2 net assimilation, which was the lowest in summer. ER followed a significant seasonal pattern, whatever the drought intensity, with mean ER maxima of 78.5 and 104.8 µgC gDM−1 h−1 in July (ND) and August (AD) respectively. Isoprene emission factor increased significantly by a factor of 2 in August and September under AD (137.8 and 74.3 µgC gDM−1 h−1) compared to ND (75.3 and 40.21 µgC gDM−1 h−1), but no changes occurred on ER. An isoprene algorithm (G14) was developed using an optimised artificial neural network trained on our experimental dataset (ER + O3HP climatic and edaphic parameters cumulated over 0 to 21 days before measurements). G14 assessed more than 80 % of the observed ER seasonal variations, whatever the drought intensity. In contrast, ER was poorly assessed under water stress by MEGAN empirical isoprene model, in particular under AD. Soil water (SW) content was the dominant parameter to account for the observed ER variations, regardless the water stress treatment. ER was more sensitive to higher frequency environmental changes under AD (0 to −7 days) compared to ND (7 days). Using IPCC RCP2.6 and RCP8.5 climate scenarios, SW and temperature calculated by the ORCHIDEE land surface model, and G14, an annual 3 fold ER relative increase was found between present (2000–2010) and future (2090–2100) for RCP8.5 scenario compared to a 70 % increase for RCP2.6. Future ER remained mainly sensitive to SW (both scenarios) and became dependent to higher frequency environmental changes under RCP8.5.

scholarly journals Seasonal variations of <i>Quercus pubescens</i> isoprene emissions from an <i>in natura</i> forest under drought stress and sensitivity to future climate change in the Mediterranean area

2018 ◽  
Vol 15 (15) ◽  
pp. 4711-4730 ◽  
Author(s):  
Anne-Cyrielle Genard-Zielinski ◽  
Christophe Boissard ◽  
Elena Ormeño ◽  
Juliette Lathière ◽  
Ilja M. Reiter ◽  
...  
Keyword(s):  
Seasonal Variations ◽  
Environmental Changes ◽  
Local Level ◽  
Future Climate Change ◽  
Surface Model ◽  
Quercus Pubescens ◽  
Drought Intensity ◽  
Isoprene Emission ◽  
Precipitation Decrease ◽  
The Mediterranean

Abstract. At a local level, biogenic isoprene emissions can greatly affect the air quality of urban areas surrounded by large vegetation sources, such as in the Mediterranean region. The impacts of future warmer and drier conditions on isoprene emissions from Mediterranean emitters are still under debate. Seasonal variations of Quercus pubescens gas exchange and isoprene emission rates (ER) were studied from June 2012 to June 2013 at the O3HP site (French Mediterranean) under natural (ND) and amplified (AD, 32 %) drought. While AD significantly reduced stomatal conductance to water vapour throughout the research period excluding August, it did not significantly preclude CO2 net assimilation, which was lowest in summer (≈-1 µmolCO2 m−2 s−1). ER followed a significant seasonal pattern regardless of drought intensity, with mean ER maxima of 78.5 and 104.8 µgC gDM-1 h−1 in July (ND) and August (AD) respectively and minima of 6 and < 2 µgC gDM-1 h−1 in October and April respectively. The isoprene emission factor increased significantly by a factor of 2 in August and September under AD (137.8 and 74.3 µgC gDM-1 h−1) compared with ND (75.3 and 40.21 µgC gDM-1 h−1), but no significant changes occurred on ER. Aside from the June 2012 and 2013 measurements, the MEGAN2.1 (Model of Emissions of Gases and Aerosols from Nature version 2.1) model was able to assess the observed ER variability only when its soil moisture activity factor γSM was not operating and regardless of the drought intensity; in this case more than 80 % and 50 % of ER seasonal variability was assessed in the ND and AD respectively. We suggest that a specific formulation of γSM be developed for the drought-adapted isoprene emitter, according to that obtained for Q. pubescens in this study (γSM= 0.192e51.93 SW with SW the soil water content). An isoprene algorithm (G14) was developed using an optimised artificial neural network (ANN) trained on our experimental dataset (ER + O3HP climatic and edaphic parameters cumulated over 0 to 21 days prior to the measurements). G14 assessed more than 80 % of the observed ER seasonal variations, regardless of the drought intensity. ERG14 was more sensitive to higher (0 to −7 days) frequency environmental changes under AD in comparison to ND. Using IPCC RCP2.6 and RCP8.5 climate scenarios, and SW and temperature as calculated by the ORCHIDEE land surface model, ERG14 was found to be mostly sensitive to future temperature and nearly insensitive to precipitation decrease (an annual increase of up to 240 % and at the most 10 % respectively in the most severe scenario). The main impact of future drier conditions in the Mediterranean was found to be an enhancement (+40 %) of isoprene emissions sensitivity to thermal stress.

scholarly journals Evaluation of Groundwater Simulations in Benin from the ALMIP2 Project

2019 ◽  
Vol 20 (2) ◽  
pp. 339-354
Author(s):  
Mehnaz Rashid ◽  
Rong-You Chien ◽  
Agnès Ducharne ◽  
Hyungjun Kim ◽  
Pat J.-F. Yeh ◽  
...  
Keyword(s):  
Seasonal Variations ◽  
Surface Runoff ◽  
Land Surface ◽  
Water Budget ◽  
Land Surface Model ◽  
Substantial Improvement ◽  
Base Flow ◽  
Specific Yield ◽  
Surface Model ◽  
Multidisciplinary Analysis

AbstractA comprehensive estimation of water budget components, particularly groundwater storage (GWS) and fluxes, is crucial. In this study, we evaluate the terrestrial water budget of the Donga basin (Benin, West Africa), as simulated by three land surface models (LSMs) used in the African Monsoon Multidisciplinary Analysis Land Surface Model Intercomparison Project, phase 2 (ALMIP2): CLM4, Catchment LSM (CLSM), and Minimal Advanced Treatments of Surface Interaction and Runoff (MATSIRO). All three models include an unconfined groundwater component and are driven by the same ALMIP2 atmospheric forcing from 2005 to 2008. Results show that all three models simulate substantially shallower water table depth (WTD) with smaller seasonal variations, approximately 1–1.5 m compared to the observed values that range between 4 and 9.6 m, while the seasonal variations of GWS are overestimated by all the models. These seemingly contradictory simulation results can be explained by the overly high specific yield prescribed in all models. All models achieve similar GWS simulations but with different fractions of precipitation partitioning into surface runoff, base flow, and evapotranspiration (ET), suggesting high uncertainty and errors in the terrestrial and groundwater budgets among models. The poor performances of models can be attributed to bias in the hydrological partitioning (base flow vs surface runoff) and sparse subsurface data. This analysis confirms the importance of subsurface hydrological processes in the current generation of LSMs and calls for substantial improvement in both surface water budget (which controls groundwater recharge) and the groundwater system (hydrodynamic parameters, vertical geometry).

Coupling an individual-based boreal forest model with a permafrost land-surface model to forecast biomass development in boreal larch forests at the Siberian treeline

2020 ◽  
Author(s):  
Simone Stünzi ◽  
Stefan Kruse ◽  
Julia Boike ◽  
Ulrike Herzschuh ◽  
Moritz Langer
Keyword(s):  
Land Surface ◽  
Boreal Forests ◽  
Environmental Changes ◽  
Carbon Sink ◽  
Land Surface Model ◽  
Radiation Budget ◽  
Surface Model ◽  
Data Set ◽  
Forest Model ◽  
Larch Forests

&lt;p&gt;The fate of boreal forests under global warming and forced rapid environmental changes is still highly uncertain, in terms of remaining a carbon sink or becoming a future carbon source. Forest dynamics and resulting ecosystem services are strongly interlinked in the vast permafrost-covered regions of the Siberian treeline ecotone. Consequently, understanding the role of current and future active layer dynamics is crucial for the prediction of aboveground biomass and thus carbon stock developments.&lt;/p&gt;&lt;p&gt;We present a coupled model version combining CryoGrid, a sophisticated one-dimensional permafrost land surface model adapted for the use in forest ecosystems, with LAVESI, a detailed, individual-based and spatially explicit larch forest model. Subsequently, parameterizing against an extensive field data set of &gt;100 forest inventories conducted along the treeline of larch-dominated boreal forests in Siberia (97-169&amp;#176; E), we run simulations covering the upcoming decades under contrasting climatic change scenarios.&lt;/p&gt;&lt;p&gt;The model setup can reproduce the energy transfer and thermal regime in permafrost ground as well as the radiation budget, nitrogen and photosynthetic profiles, canopy turbulence and leaf fluxes and predict the expected establishment, die-off and treeline movements of larch forests. Our results will show vegetation and permafrost dynamics, quantify the magnitudes of different feedback processes between permafrost, vegetation, and climate and reveal their impact on carbon stocks in Northern Siberia.&lt;/p&gt;

GRACE-derived seasonal variations, a key to understanding aquifer sources, recharge and groundwater flow patterns

2020 ◽  
Author(s):  
karem Abdelmohsen ◽  
Mohamed Sultan ◽  
Himanshu Save
Keyword(s):  
Groundwater Flow ◽  
Seasonal Variations ◽  
Spherical Harmonic ◽  
Land Surface ◽  
Land Surface Model ◽  
Buffer Zone ◽  
Forward Modeling ◽  
Surface Model ◽  
Aquifer System ◽  
Lake Nasser

&lt;p&gt;The Nubian Sandstone Aquifer System (NSAS) in northeast Africa is formed of three subbasins, the Dakhla, Kufra, and the Northern Sudan Platform subbasins. The Dakhla subbasin (DSB) receives negligible precipitation (&lt;10 mm/yr), yet displays significant seasonal variations in GRACETWS (average: 50 mm/yr, up to 77 mm/yr) across the entire subbasin. The origin of these variations could be related to one or more of the following factors: (1) leakage out from Lake Nasser, (2) leakage in from surroundings (Kufra basin [west NSAS], Northern Sudan Platform [south NSAS], Mediterranean sea [north NSAS], and Red Sea [east NSAS], and (3) recharge and rapid groundwater flow from Lake Nasser and the northern Sudan Platform. Three approaches were used to investigate the contribution of leakage (factors 1 and 2) to the observed GRACETWS signal over the DSB subbasin: (1) forward modeling (in spherical harmonic domain) of the maximum variations in Lake Nasser levels was applied to test whether the observed seasonal variation in GRACETWS across the DSB can be accounted for by leakage from Lake Nasser alone; (2) estimate (in spherical harmonic domain) the leakage in signal using the simulated TWS from the widely applied Land Surface Model (LSM), GLDAS (Global Land Data Simulation System); and (3) apply iterative forward modeling (iterations: n=30) to reconstruct the true mass variations of GRACETWS over the DSB. Findings suggest: (1) the leakage in signal over the DSB cannot account for the observed seasonal GRACETWS patterns and neither can the leakage out from Lake Nasser; (2) the leakage out signal is centered over Lake Nasser and extends to its immediate surroundings with a maximum radius of 250 km (upper boundary of leakage error); (3) the iterative modeling indicates that the maximum leakage within the 250 km buffer zone around the lake amounted to 22.6 % of the observed GRACETWS signal; (4) minimal leakage (up to 10 mm) from northerly precipitation is observed along the northern sections (~200 km deep) of the NSAS and negligible (&lt; 4 mm) leakage is detected over the remaining sections of the DSB; and (5) the observed seasonal variations in GRACETWS over the DSB is related to an increase in groundwater storage related to seasonal recharge from Lake Nasser and rapid groundwater flow along a network of faults, fractures, and karst topography across the entire DSB.&lt;/p&gt;

scholarly journals Development of a Flash Drought Intensity Index

Atmosphere ◽  
2021 ◽  
Vol 12 (6) ◽  
pp. 741
Author(s):  
Jason A. Otkin ◽  
Yafang Zhong ◽  
Eric D. Hunt ◽  
Jordan I. Christian ◽  
Jeffrey B. Basara ◽  
...  
Keyword(s):  
Soil Moisture ◽  
Land Surface ◽  
Land Surface Model ◽  
Drought Severity ◽  
Surface Model ◽  
Severe Drought ◽  
Rapid Intensification ◽  
Drought Intensity ◽  
Intensity Index ◽  
Large Yield

Flash droughts are characterized by a period of rapid intensification over sub-seasonal time scales that culminates in the rapid emergence of new or worsening drought impacts. This study presents a new flash drought intensity index (FDII) that accounts for both the unusually rapid rate of drought intensification and its resultant severity. The FDII framework advances our ability to characterize flash drought because it provides a more complete measure of flash drought intensity than existing classification methods that only consider the rate of intensification. The FDII is computed using two terms measuring the maximum rate of intensification (FD_INT) and average drought severity (DRO_SEV). A climatological analysis using soil moisture data from the Noah land surface model from 1979–2017 revealed large regional and interannual variability in the spatial extent and intensity of soil moisture flash drought across the US. Overall, DRO_SEV is slightly larger over the western and central US where droughts tend to last longer and FD_INT is ~75% larger across the eastern US where soil moisture variability is greater. Comparison of the FD_INT and DRO_SEV terms showed that they are strongly correlated (r = 0.82 to 0.90) at regional scales, which indicates that the subsequent drought severity is closely related to the magnitude of the rapid intensification preceding it. Analysis of the 2012 US flash drought showed that the FDII depiction of severe drought conditions aligned more closely with regions containing poor crop conditions and large yield losses than that captured by the intensification rate component (FD_INT) alone.

L'apport de la télédétection spatiale à la modélisation des surfaces continentales

2020 ◽  
pp. 052
Author(s):  
Jean-Christophe Calvet ◽  
Jean-Louis Champeaux
Keyword(s):  
Satellite Data ◽  
Land Surface ◽  
Land Surface Model ◽  
Static Model ◽  
Geographic Information ◽  
Surface Model ◽  
Model Parameters

Cet article présente les différentes étapes des développements réalisés au CNRM des années 1990 à nos jours pour spatialiser à diverses échelles les simulations du modèle Isba des surfaces terrestres. Une attention particulière est portée sur l'intégration, dans le modèle, de données satellitaires permettant de caractériser la végétation. Deux façons complémentaires d'introduire de l'information géographique dans Isba sont présentées : cartographie de paramètres statiques et intégration au fil de l'eau dans le modèle de variables observables depuis l'espace. This paper presents successive steps in developments made at CNRM from the 1990s to the present-day in order to spatialize the simulations of the Isba land surface model at various scales. The focus is on the integration in the model of satellite data informative about vegetation. Two complementary ways to integrate geographic information in Isba are presented: mapping of static model parameters and sequential assimilation of variables observable from space.

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