Multiscale analysis of evapotranspiration and carbon assimilation for a long time series of micrometeorological observation in a typical semi-arid Mediterranean ecosystem

2020 ◽  
Author(s):  
Roberto Corona ◽  
Nicola Montaldo ◽  
Gabriel G. Katul
Keyword(s):  
Time Series ◽  
Soil Moisture ◽  
Vapor Pressure ◽  
Spectral Density ◽  
Time Scales ◽  
Vapor Pressure Deficit ◽  
Mediterranean Ecosystem ◽  
The Mediterranean ◽  
Annual Time ◽  
Semi Arid

<p>The evapotranspiration (<em>ET</em>) process is a key term of soil water balance. In the Mediterranean climates <em>ET </em>represents the main loss term, that could return up to 70% of annual precipitation to the atmosphere. Due to the high seasonal and annual variability of precipitation typical of this this ecosystems, <em>ET</em>may be 90% of annual precipitation. Considering that in the Mediterranean areas most of the available water for drinking purpose and for agriculture depends on the water stored in the artificial basins during the rainy period, the quantification of <em>ET </em>and its dynamics is of great importance.</p><p><em>ET </em>exhibits a temporal pattern that varies from seconds to decades, and it is mainly dependent as well as by precipitation, also by its guiding factors (e.g. soil water moisture, solar radiation and vapor pressure deficit). Hence, identify the main factors that influence <em>ET  </em>becomes fundamental to understand its temporal variability, and is needed when modeling <em>ET </em>over different timescales.</p><p>The case study is the Orroli site in Sardinia (Italy), a typical semi-arid Mediterranean ecosystem, for which are available eddy covariance measurements of sensible heat (<em>H</em>), latent heat (<em>LE</em>) fluxes, and soil moisture, radiation, air temperature and air humidity measurements, over 15 years. The Mediterranean site is typically characterized by strong interannual variability of meteorological conditions, which can drastically impacts water resources variability during spring and summers, the key seasons for the water resources planning and management of the region.</p><p>Based on the half-hour time series, the meteorological measurements were considered into investigation, and their variability has been detected at different time scale, from seconds to year. The conventional Pearson correlation coefficient between <em>ET</em> and its guiding factors has been estimated, and showed the main influence of soil moisture and vapor pressure deficit on <em>ET</em> process, and suggested that the their control on <em>ET</em> vary with timescale.</p><p>Furthermore, the orthonormal wavelet transformation (a spectral analysis methodology), was used to investigate the time scale variability of <em>ET</em> in the frequency domain, and identify the role of its guiding factors for different time scales. The <em>ET</em> spectral density has significant peaks at the daily, seasonal and annual time-scales. In particular, the variability of the <em>ET</em> spectral density exhibits two order magnitude more than the daily variability. The wavelet cospectra of <em>ET</em> and its guiding factors showed that the interaction is strongest for the seasonal and the annual time scales.</p>

scholarly journals Land–atmosphere feedbacks exacerbate concurrent soil drought and atmospheric aridity

2019 ◽  
Vol 116 (38) ◽  
pp. 18848-18853 ◽  
Author(s):  
Sha Zhou ◽  
A. Park Williams ◽  
Alexis M. Berg ◽  
Benjamin I. Cook ◽  
Yao Zhang ◽  
...  
Keyword(s):  
Soil Moisture ◽  
Vapor Pressure ◽  
High Probability ◽  
Vapor Pressure Deficit ◽  
Cmip5 Models ◽  
Soil Drought ◽  
Global Land ◽  
High Vapor ◽  
Mean Climate ◽  
Negative Coupling

Compound extremes such as cooccurring soil drought (low soil moisture) and atmospheric aridity (high vapor pressure deficit) can be disastrous for natural and societal systems. Soil drought and atmospheric aridity are 2 main physiological stressors driving widespread vegetation mortality and reduced terrestrial carbon uptake. Here, we empirically demonstrate that strong negative coupling between soil moisture and vapor pressure deficit occurs globally, indicating high probability of cooccurring soil drought and atmospheric aridity. Using the Global Land Atmosphere Coupling Experiment (GLACE)-CMIP5 experiment, we further show that concurrent soil drought and atmospheric aridity are greatly exacerbated by land–atmosphere feedbacks. The feedback of soil drought on the atmosphere is largely responsible for enabling atmospheric aridity extremes. In addition, the soil moisture–precipitation feedback acts to amplify precipitation and soil moisture deficits in most regions. CMIP5 models further show that the frequency of concurrent soil drought and atmospheric aridity enhanced by land–atmosphere feedbacks is projected to increase in the 21st century. Importantly, land–atmosphere feedbacks will greatly increase the intensity of both soil drought and atmospheric aridity beyond that expected from changes in mean climate alone.

Conflicting drivers of land carbon uptake variability reconciled by land-atmosphere coupling

2020 ◽  
Author(s):  
Vincent Humphrey ◽  
Alexis Berg ◽  
Philippe Ciais ◽  
Christian Frankenberg ◽  
Pierre Gentine ◽  
...  
Keyword(s):  
Soil Moisture ◽  
Vapor Pressure ◽  
Water Availability ◽  
Vapor Pressure Deficit ◽  
Sensitivity Analyses ◽  
Carbon Uptake ◽  
Annual Variability ◽  
Vegetation Activity ◽  
The Impact

<p>Obtaining reliable estimates of the sensitivity of carbon fluxes to water availability, temperature and vapor pressure deficit is essential for constraining climate-carbon feedbacks in Earth system models. However, these variables often co-vary because of soil moisture – atmosphere feedbacks, especially in situations where they are most susceptible to strongly impact ecosystems (e.g. during droughts and heatwaves), leading to potentially conflicting results when sensitivities are assessed independently. In particular, there is conflicting evidence on the role of temperature versus water availability in explaining these variations at the global scale.</p><p>Here, we show that accounting for the effect of soil moisture – atmosphere coupling resolves much of this controversy. Using idealized climate model experiments, we find that variability in soil moisture accounts for 90% of the inter-annual variability in land carbon uptake, mainly through its impact on photosynthesis. Without SM variability, the inter-annual variability (IAV) of land carbon uptake is almost eliminated. We show that the effects of soil moisture can be decomposed into 1) a direct ecosystem response to soil water stress and 2) a dominant indirect response to extreme temperature and vapor pressure deficit triggered by land-atmosphere coupling and controlled by anomalous soil moisture conditions.  Importantly, these two mechanisms do not necessarily have the same spatial extent, and some regions can be more sensitive to indirect effects than to direct effects.</p><p>These two pathways explain why results from coupled climate models suggest a dominant role of soil moisture, while uncoupled simulations diagnose a strong temperature effect. These findings have strong implications for offline model sensitivity analyses as well as field scale manipulation experiments (i.e. rainfall exclusion studies) where the impact of drought on carbon exchange and vegetation activity is often studied by intervening solely on soil moisture content with little consideration of the physical feedbacks on temperature and air humidity occurring in natural conditions.</p>

Sentinel-1 application to rainfall response and geomorphic mapping

2021 ◽  
Author(s):  
Stephanie Olen ◽  
Bodo Bookhagen
Keyword(s):  
Time Series ◽  
Soil Moisture ◽  
Snow Cover ◽  
Rainfall Event ◽  
Rainfall Events ◽  
Northwestern Argentina ◽  
Standing Water ◽  
Land Surfaces ◽  
High Infiltration ◽  
Semi Arid

<p>Rainfall is one of the primary geomorphic drivers on Earth’s surface. How a surface responds to rainfall directly impacts erosional, geomorphic, and natural hazard processes. In the absence of vegetation, whether a land surface retains rainfall as soil moisture or whether rainfall is quickly infiltrated or run off is largely a function of geomorphologic and geologic conditions. In this study, we combine a time series of synthetic aperture radar (SAR) backscatter with daily precipitation to analyze the response of arid and semi-arid land surfaces to rainfall from the event to seasonal scale. The study focuses on northwestern Argentina, where we have extensive field knowledge of local geomorphic features, and is implemented using the cloud computing capacities of Google Earth Engine (GEE).</p><p>Th Sentinel-1 satellites provide high spatial (10 m) and temporal resolution images of Earth’s surface, irrespective of cloud cover. We created a 3 year time series from 2018 through 2020 of Sentinel-1 sigma-naught (σ<sub>0</sub>) backscatter from Ground Range Detected (GRD) products available on GEE. Combining the ascending and descending orbits of the Sentinel-1A and -1B satellites into a single time series provides 3 to 6 day temporal resolution in our area of interest. The Global Precipitation Measurement Mission (GPM) was aggregated to daily and monthly precipitation measurements to identify single rainfall events and the seasonal rainfall signal.</p><p>The response and recovery of SAR backscatter to individual rainfall events across different land surfaces was calculated over 4 to 6 week periods centered on and following a specific rainfall date, respectively. The temporal trend of the backscatter data in these time windows is calculated for every pixel in the backscatter stack to create a map how the surface responds to a large rainfall event. The location of standing water, increased soil moisture, and high infiltration surfaces are detectable in the response maps. The recovery maps provide a proxy for the rate of drying following the rainfall event.</p><p>In the monsoon-dominated region of northwestern Argentina, both precipitation and SAR backscatter show a clear, periodic seasonal signal over our three-year time series. By aggregating all data to monthly resolution, we can calculate pixel-wise linear regressions and correlation coefficients between precipitation and SAR backscatter. Regressions and correlation analysis are done at the resolution of the Sentinel-1 data and are used to identify whether a surface retains soil moisture, has high infiltration, or experiences seasonal standing water or snow cover. Areas dominated by highly weathered granites and sandstones that can retain soil moisture, for example, have strong positive correlation between rainfall and backscatter due to the increased dielectric constant of wet sediment. In contrast, gravel terraces where rainfall can easily infiltrate the surface show little correlation between backscatter and precipitation. The result is a high resolution map characterizing the propensity for soil moisture retention, high infiltration, and standing water and snow cover. Future work will focus on using these relationships to classify geomorphic surfaces across the arid and semi-arid central Andes.</p>

Determinants of calcite flux in planktonic foraminifera on seasonal and interannual time scales

2020 ◽  
Author(s):  
Peter Kiss ◽  
Lukas Jonkers ◽  
Natália Hudáčková ◽  
Runa Turid Reuter ◽  
Michal Kučera
Keyword(s):  
Time Series ◽  
Time Scales ◽  
Time Scale ◽  
Planktonic Foraminifera ◽  
Sediment Traps ◽  
Shell Size ◽  
Global Estimate ◽  
Export Flux ◽  
Species Specific ◽  
Annual Time

<p>Planktonic foraminifera precipitate calcareous shells, which after the death of the organisms are exported from the sea surface to the sea floor, where they are preserved on geologically relevant timescales. The export flux of planktonic foraminifera shells constitutes globally up to a half, and in the studied region off Cap Blanc (Atlantic Ocean) about one third, of the marine pelagic calcite flux. Given their importance for the marine calcite budget and for the pelagic carbonate counter pump, which counteracts the biological pump in terms of oceanic capacity for intake of CO<sub>2</sub>, it is crucial to gain an understanding of factors modulating the export flux of planktonic foraminifera calcite. In principle, variability in the export flux of planktonic foraminifera calcite could depend within one species on i) shell flux, ii) shell size and iii) calcification intensity, and where shell size and calcification intensity differ among species also on the species composition of the deposited assemblage. To assess the importance of these aspects in modulating the export flux of planktonic foraminifera calcite, we investigated two annual time series (from 1990-1991 and 2007-2008) from sediment traps moored in the Cap Blanc upwelling area. We assessed the predictability of foraminifera calcite flux variability on seasonal and interannual time scales, by determining the variability in species-specific shell fluxes, shell sizes and weights with bi-weekly resolution. We find a remarkable discrepancy in the contribution of the controlling factors between seasonal and interannual scales. On the seasonal time scale, 80% of the variability of the calcite flux is explained by shell flux. On the inter-annual time scale, on the other hand, variations in shell size and calcification intensity are key to explain the calcite flux, since the time series from 2007-2008 yielded 58% larger and 11% heavier specimens. These results imply that for the global estimate of planktonic foraminifera calcite flux, shell flux is likely the most relevant predictor. However, a prediction of the temporal evolution of the calcite flux will likely require estimates of changes in shell size and calcification intensity of the involved foraminifera species.</p>

Diel ecosystem conductance response to vapor pressure deficit is suboptimal and independent of soil moisture

2018 ◽  
Vol 250-251 ◽  
pp. 24-34 ◽  
Author(s):  
Changjie Lin ◽  
Pierre Gentine ◽  
Yuefei Huang ◽  
Kaiyu Guan ◽  
Hyungsuk Kimm ◽  
...  
Keyword(s):  
Soil Moisture ◽  
Vapor Pressure ◽  
Vapor Pressure Deficit

scholarly journals Sap Flow Dynamics and Responses to Grazing and Seasonal Changes in Soil Moisture for Acacia Ancistroclada and Comberatum Molle in a Kenyan Savanna

2020 ◽  
Author(s):  
Joseph Ondier ◽  
Dennis Otieno ◽  
Daniel Okach ◽  
John Onyango
Keyword(s):  
Soil Moisture ◽  
Vapor Pressure ◽  
Flux Density ◽  
Sap Flow ◽  
Seasonal Changes ◽  
Vapor Pressure Deficit ◽  
Livestock Grazing ◽  
Sap Flux ◽  
Sap Flux Density ◽  
Rainfall Patterns

Abstract The Kenyan savanna, which is dominated by Acacia ancistroclada and Comberatum molle, has experienced notable changes in rainfall patterns and increased livestock grazing. A significant decrease in trees spread from 5 % to less than 1 % has been documented for the ecosystem and could be linked to the increased livestock grazing and changes in rainfall patterns, however, scientific evidence is lacking. We utilized sap flow to analyze the hydraulic responses of the prevailing trees to livestock grazing and seasonal changes in soil moisture. Environmental factors including precipitation, air temperature, soil moisture at - 0.3 m, and vapor pressure deficit were simultaneously measured. The results showed that the diurnal variation in sap flux density exhibited a single peak curve at around midday and correlated strongly with vapor pressure deficit and air temperature. Sap flux density was higher in the grazed (27.47 ± 8.65 g m-2s-1) than the fenced plots (20.17 ± 7.27 g m-2s-1). In all the plots, sap flux density followed seasonality in rainfall patterns, increasing and decreasing in wet and dry seasons respectively. The higher crown projected area was responsible for higher sap flow in the grazed plots. The diurnal variation in sap flux density showed that sap flow was coupled to the atmosphere with relatively low boundary layer resistance and the seasonal variation in sap flow was controlled by stomatal regulation. These findings point to the possibility that the dominant tree species in Lambwe are isohydric species. However, additional measurements need to be conducted on the eligibility of the species to confirm the conclusion.

Conifers and broadleaf species: stomatal sensitivity differs in western Oregon

1984 ◽  
Vol 14 (6) ◽  
pp. 905-908 ◽  
Author(s):  
J. D. Marshall ◽  
R. H. Waring
Keyword(s):  
Soil Moisture ◽  
Vapor Pressure ◽  
Vapor Pressure Deficit ◽  
Stomatal Closure ◽  
High Vapor Pressure ◽  
Disturbed Areas ◽  
High Vapor ◽  
Stomatal Sensitivity ◽  
Broadleaf Species

Increasing stomatal closure was exhibited by two conifer and six broadleaf species as vapor pressure deficit increased. Conifers were more sensitive to high vapor pressure deficit than were the broadleaved species. One shrub, snowbrush (Ceanothusvelutinus Dougl. ex Hook.), exhibited no stomatal closure as vapor pressure deficit increased. These traits, when interpreted in terms of known soil moisture depletion patterns, help explain why broadleaved species initially colonize disturbed areas in western Oregon, but are later replaced by long-lived conifers.

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