scholarly journals Land surface scheme conceptualisation and parameter values for three sites with contrasting soils and climate

2000 ◽  
Vol 4 (2) ◽  
pp. 283-294 ◽  
Author(s):  
M. Soet ◽  
R. J. Ronda ◽  
J. N. M. Stricker ◽  
A. J. Dolman
Keyword(s):  
Land Surface ◽  
Hydraulic Properties ◽  
Bare Soil ◽  
Soil Evaporation ◽  
Rooting Depth ◽  
Surface Model ◽  
Soil Hydraulic Properties ◽  
Bare Soil Evaporation ◽  
Soil Hydraulic ◽  
Parameter Values

Abstract. The objective of the present study is to test the performance of the ECMWF land surface module (LSM) developed by Viterbo and Beljaars (1995) and to identify primary future adjustments, focusing on the hydrological components. This was achieved by comparing off-line simulations against observations and a detailed state-of-the-art model over a range of experimental conditions. Results showed that the standard LSM, which uses fixed vegetation and soil parameter values, systematically underestimated evapotranspiration, partly due to underestimating bare soil evaporation, which appeared to be a conceptual problem. In dry summer conditions, transpiration was seriously underestimated. The bias in surface runoff and percolation was not of the same sign for all three locations. A sensitivity analysis, set up to explore the impact of using standard parameter values, found that implementing specific soil hydraulic properties had a significant effect on runoff and percolation at all three sites. Evapotranspiration, however affected only slightly at the temperate humid climate sites. Under semi-arid conditions, introducing site specific soil hydraulic properties plus a realistic rooting depth improved simulation results considerably. Future adjustments to the standard LSM should focus on parameter values of soil hydraulic functions and rooting depths and, conceptually, on the bare soil evaporation parameterisation and the soil bottom boundary condition. Implications of changing soil hydraulic properties for future large-simulations were explored briefly. For Europe, soil data requirements can be fulfilled partly by the recent data base HYPRES. Sandy and loamy sand soils will then cover about 65% of Europe, whereas in the present model 100% of the area is loam. Keywords: land surface model; soil hydraulic properties; water balance simulation

scholarly journals Testing water fluxes and storage from two hydrology configurations within the ORCHIDEE land surface model across US semi-arid sites

2020 ◽  
Vol 24 (11) ◽  
pp. 5203-5230
Author(s):  
Natasha MacBean ◽  
Russell L. Scott ◽  
Joel A. Biederman ◽  
Catherine Ottlé ◽  
Nicolas Vuichard ◽  
...  
Keyword(s):  
Soil Moisture ◽  
Land Surface ◽  
Moisture Diffusion ◽  
Bare Soil ◽  
Soil Evaporation ◽  
Arid Ecosystems ◽  
Layer Model ◽  
Soil Fraction ◽  
Bare Soil Evaporation ◽  
Semi Arid

Abstract. Plant activity in semi-arid ecosystems is largely controlled by pulses of precipitation, making them particularly vulnerable to increased aridity that is expected with climate change. Simple bucket-model hydrology schemes in land surface models (LSMs) have had limited ability in accurately capturing semi-arid water stores and fluxes. Recent, more complex, LSM hydrology models have not been widely evaluated against semi-arid ecosystem in situ data. We hypothesize that the failure of older LSM versions to represent evapotranspiration, ET, in arid lands is because simple bucket models do not capture realistic fluctuations in upper-layer soil moisture. We therefore predict that including a discretized soil hydrology scheme based on a mechanistic description of moisture diffusion will result in an improvement in model ET when compared to data because the temporal variability of upper-layer soil moisture content better corresponds to that of precipitation inputs. To test this prediction, we compared ORCHIDEE LSM simulations from (1) a simple conceptual 2-layer bucket scheme with fixed hydraulic parameters and (2) an 11-layer discretized mechanistic scheme of moisture diffusion in unsaturated soil based on Richards equations, against daily and monthly soil moisture and ET observations, together with data-derived estimates of transpiration / evapotranspiration, T∕ET, ratios, from six semi-arid grass, shrub, and forest sites in the south-western USA. The 11-layer scheme also has modified calculations of surface runoff, water limitation, and resistance to bare soil evaporation, E, to be compatible with the more complex hydrology configuration. To diagnose remaining discrepancies in the 11-layer model, we tested two further configurations: (i) the addition of a term that captures bare soil evaporation resistance to dry soil; and (ii) reduced bare soil fractional vegetation cover. We found that the more mechanistic 11-layer model results in a better representation of the daily and monthly ET observations. We show that, as predicted, this is because of improved simulation of soil moisture in the upper layers of soil (top ∼ 10 cm). Some discrepancies between observed and modelled soil moisture and ET may allow us to prioritize future model development and the collection of additional data. Biases in winter and spring soil moisture at the forest sites could be explained by inaccurate soil moisture data during periods of soil freezing and/or underestimated snow forcing data. Although ET is generally well captured by the 11-layer model, modelled T∕ET ratios were generally lower than estimated values across all sites, particularly during the monsoon season. Adding a soil resistance term generally decreased simulated bare soil evaporation, E, and increased soil moisture content, thus increasing transpiration, T, and reducing the negative bias between modelled and estimated monsoon T∕ET ratios. This negative bias could also be accounted for at the low-elevation sites by decreasing the model bare soil fraction, thus increasing the amount of transpiring leaf area. However, adding the bare soil resistance term and decreasing the bare soil fraction both degraded the model fit to ET observations. Furthermore, remaining discrepancies in the timing of the transition from minimum T∕ET ratios during the hot, dry May–June period to high values at the start of the monsoon in July–August may also point towards incorrect modelling of leaf phenology and vegetation growth in response to monsoon rains. We conclude that a discretized soil hydrology scheme and associated developments improve estimates of ET by allowing the modelled upper-layer soil moisture to more closely match the pulse precipitation dynamics of these semi-arid ecosystems; however, the partitioning of T from E is not solved by this modification alone.

Simulating infiltration and the water balance in cropping systems with APSIM-SWIM

Soil Research ◽  
2002 ◽  
Vol 40 (2) ◽  
pp. 221 ◽  
Author(s):  
R. D. Connolly ◽  
M. Bell ◽  
N. Huth ◽  
D. M. Freebairn ◽  
G. Thomas
Keyword(s):  
Water Balance ◽  
Soil Water ◽  
Hydraulic Properties ◽  
Cropping Systems ◽  
Soil Condition ◽  
Crop Growth ◽  
Soil Hydraulic Properties ◽  
Crop Models ◽  
Soil Hydraulic ◽  
Parameter Values

We test APSIM-SWIM's ability to simulate infiltration and interactions between the soil water balance and grain crop growth using soil hydraulic properties derived from independent, point measurements. APSIMSWIM is a continuous soil-crop model that simulates infiltration, surface crusting, and soil condition in more detail than most other soil-crop models. Runoff, soil water, and crop growth information measured at sites in southern Queensland was used to test the model. Parameter values were derived directly from soil hydraulic properties measured using rainfall simulators, disc permeameters and ponded rings, and pressure plate apparatus. In general, APSIM-SWIM simulated infiltration, runoff, soil water and the water balance, and yield as accurately and reliably as other soil crop models, indicating the model is suitable for evaluating effects of infiltration and soil-water relations on crop growth. Increased model detail did not hinder application, instead improving parameter transferability and utility, but improved methods of characterising crusting, soil hydraulic conductivity, and macroporosity under field conditions would improve ease of application, prediction accuracy, and reliability of the model. Model utility and accuracy would benefit from improved representation of temporal variation in soil condition, including effects of tillage and consolidation on soil condition and bypass flow in cracks. infiltration, crop models, APSIM, water balance, soil structure.

Modeling root water uptake depth driven by climate and soil texture using a simple bucket model approach

2021 ◽  
Author(s):  
Ruth Adamczewski ◽  
Sven Westermann ◽  
Anke Hildebrandt
Keyword(s):  
Soil Water ◽  
Hydraulic Properties ◽  
Water Retention ◽  
Root Water Uptake ◽  
Rooting Depth ◽  
Soil Hydraulic Properties ◽  
Soil Water Retention ◽  
Precipitation Patterns ◽  
Biogeochemical Models ◽  
Soil Hydraulic

<p>Root water uptake (RWU) in grasslands is determined by species composition, climate and soil hydraulic properties. Generally, plant communities are adapted to their environment, showing different rooting patterns along climate gradients. Due to climate change, ecosystems are exposed to shifts in precipitation patterns and rising temperatures, causing the need to adapt rooting strategies. RWU is mainly driven by plant transpiration and soil hydraulic status in the rooting zone. Soil hydraulic properties depend strongly on soil texture, which has been observed to influence rooting depth, increasing the root length from fine to coarse soils. Secondly, precipitation patterns affect the typical soil moisture status, and subsequently the rooting depth. Global models suggest that in dry environments RWU should move deeper, to enhance the plant available soil water. However, few studies have at the same time considered the effect of climate and soil properties on RWU depth, although soil properties vary substantially and probably more than precipitation patterns due to climate change.</p><p>Biogeochemical models suffer from uncertainty in subsurface hydrological processes, RWU being an important part of it. Thus, ecohydrological models are needed for an integration in larger context biogeochemical models. The trend of ecological models is towards high parameterized models, implying high uncertainty and challenging calibration for those parameters. Especially in the subsurface, parameters are often unknown and are usually impossible to derive from direct measurements. In this project, a simple, parsimonious bucket model was implemented, solving the water balance equation for a multi-layer soil profile. The objective of this work is to predict maximum required RWU depth required to satisfy potential evapotranspiration across established experimental grassland sites with different climate and soil water retention properties. For this we use soil moisture measurements, textures and hydraulic properties determined in three grassland sites of the Nutrient-Network (NutNet) across a climate gradient. We test the sensitivity of the model towards climate and soil hydraulic parameters. First model results show a high sensitivity of RWU depth besides to dynamics to climate, also to soil water retention determined by texture and organic matter content in the soils.</p>

scholarly journals Multi-variable, multi-configuration testing of ORCHIDEE land surface model water flux and storage estimates across semi-arid sites in the southwestern US

2019 ◽  
Author(s):  
Natasha MacBean ◽  
Russell L. Scott ◽  
Joel A. Biederman ◽  
Catherine Ottlé ◽  
Nicolas Vuichard ◽  
...  
Keyword(s):  
Soil Moisture ◽  
Land Surface ◽  
Moisture Diffusion ◽  
Bare Soil ◽  
Soil Evaporation ◽  
Arid Ecosystems ◽  
Soil Hydrology ◽  
Soil Fraction ◽  
Bare Soil Evaporation ◽  
Semi Arid

Abstract. Plant activity in semi-arid ecosystems is largely controlled by pulses of precipitation, making them particularly vulnerable to increased aridity expected with climate change. Simple bucket-model hydrology schemes in land surface models (LSMs) have had limited ability in accurately capturing semi-arid water stores and fluxes. Recent, more complex, LSM hydrology models have not been widely evaluated against semi-arid ecosystem in situ data. We hypothesize that the failure of older LSM versions to represent evapotranspiration, ET, in arid lands is because simple bucket models do not capture realistic fluctuations in upper layer soil moisture. We therefore predict that including a discretized soil hydrology scheme based on a mechanistic description of moisture diffusion will result in an improvement in model ET when compared to data because the temporal variability of upper layer soil moisture content better corresponds to that of precipitation inputs. To test this prediction, we compared ORCHIDEE LSM simulations from (1) a simple conceptual 2-layer bucket scheme with fixed hydrological parameters; and (2) a 11-layer discretized mechanistic scheme of moisture diffusion in unsaturated soil based on Richards equations against daily and monthly soil moisture and ET observations, together with data-derived transpiration / evaporation, T / ET, ratios, from six semi-arid grass, shrub and forest sites in the southwestern USA. The 11-layer scheme also has modified calculations of surface runoff, bare soil evaporation, and water limitation to be compatible with the more complex hydrology configuration. To diagnose remaining discrepancies in the 11-layer model, we tested two further configurations: (i) the addition of a term that captures bare soil evaporation resistance to dry soil; and (ii) reduced bare soil fraction. We found that the more mechanistic 11-layer model results better representation of the daily and monthly ET observations. We show that is likely because of improved simulation of soil moisture in the upper layers of soil (top 5 cm). Some discrepancies between observed and modelled soil moisture and ET may allow us to prioritize future model development. Adding a soil resistance term generally decreased simulated E and increased soil moisture content, thus increasing T and T / ET ratios and reducing the negative T / ET model-data bias. By reducing the bare soil fraction in the model, we illustrated that modelled leaf T is too low at sparsely vegetated sites. We conclude that a discretized soil hydrology scheme and associated developments improves estimates of ET by allowing the model to more closely match the pulse precipitation dynamics of these semi-arid ecosystems; however, the partitioning of T from bare soil evaporation is not solved by this modification alone.

Actual evaporation from bare soils - A comparison of numerical modelling and field lysimeter data

2021 ◽  
Author(s):  
Deep Chandra Joshi ◽  
Andre Peters ◽  
Sascha C. Iden ◽  
Beate Zimmermann ◽  
Wolfgang Durner
Keyword(s):  
Hydraulic Properties ◽  
Bare Soil ◽  
Systematic Difference ◽  
Potential Evaporation ◽  
Soil Hydraulic Properties ◽  
Actual Evaporation ◽  
Dry Conditions ◽  
Soil Hydraulic ◽  
Filter Approach ◽  
Bare Soils

<p>Predicting evaporation from drying soils under limited water supply conditions, where water transfer to the atmosphere is limited primarily by soil hydraulic conductivity, is challenging. The parameterization of soil hydraulic properties (SHP) plays a crucial role in reliable predictions of evaporation. In particular, there are expected differences between traditional functions that consider water flow only in capillaries and functions that additionally consider non-capillary processes, i.e., water storage and film flow on particle surfaces and in corners and channels of pores. The non-capillary processes in simulating evaporation from soil surfaces become more important when the soil dries.</p><p>The purpose of this study was to investigate the applicability of different soil hydraulic function types in modelling the actual evaporation under water-limited conditions. Data were obtained from a large bare-soil field lysimeter (2.5 m height; 1 m<sup>2</sup> surface area), where the lysimeter mass and outflow were measured in hourly time intervals. Precipitation and actual evaporation were calculated from the mass changes of the lysimeter, using a simplified version of the AWAT filter approach of Peters et al. (2017). Meteorological parameters to calculate the potential evaporation were taken from the nearest weather station. Potential evaporation rates were obtained by (i) using the FAO-56 version of the Penman-Monteith equation and (ii) scaling these values to match the bare soil potential evaporation.</p><p>The evaporation was simulated using two different models for soil hydraulic properties: i) van Genuchten Mualem (VGM) (only capillary storage and flow), and ii) Peters-Durner-Iden (PDI) (capillary and non-capillary storage and flow). The results show a systematic difference in evaporation prediction by applying the PDI and VGM models, with higher evaporation rates for the PDI model under dry conditions.</p>

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