Technical Note: A comparison of model and empirical measures of catchment scale effective energy and mass transfer

Abstract. Recent work suggests that a coupled energy and mass transfer term (EEMT), that includes the energy associated with effective precipitation and primary production, may serve as a robust prediction parameter of critical zone structure and function. However, the models used to estimate EEMT have been solely based on long term climatological data with little validation using point to catchment scale empirical data. Here we compare catchment scale EEMT estimates generated using two distinct approaches: (1) EEMT modelled using the established methodology based on estimates of monthly effective precipitation and net primary production derived from climatological data, and (2) empirical catchment scale EEMT estimated using data from 86 catchments of the Model Parameterization Experiment (MOPEX) and MOD17A3 annual net primary production (NPP) product derived from Moderate Resolution Imaging Spectroradiometer (MODIS). Results indicated positive and significant linear correspondence between model and empirical measures but with modelled EEMT values consistently greater than empirical measures of EEMT. Empirical catchment estimates of the energy associated with effective precipitation (EPPT) were calculated using a mass balance approach and base flow that accounts for water losses to quick surface runoff not accounted for in the climatologically modelled EPPT. Similarly, local controls on primary production such as solar radiation and nutrient limitation were not explicitly included in the climatologically based estimates of energy associated with primary production (EBIO) whereas these were captured in the remotely sensed MODIS NPP data. There was significant positive correlation between catchment aridity and the fraction of total energy partitioned into EBIO, where the EBIO increases as the average percentage catchment woody plant cover decreases. In summary, the data indicated strong correspondence between model and empirical measures of EEMT that agree well with catchment energy and water partitioning and plant cover.

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Technical Note: A comparison of model and empirical measures of catchment-scale effective energy and mass transfer

Hydrology and Earth System Sciences ◽

10.5194/hess-17-3389-2013 ◽

2013 ◽

Vol 17 (9) ◽

pp. 3389-3395 ◽

Cited By ~ 6

Author(s):

C. Rasmussen ◽

E. L. Gallo

Keyword(s):

Mass Transfer ◽

Primary Production ◽

Net Primary Production ◽

Plant Cover ◽

Effective Energy ◽

Catchment Scale ◽

Water Losses ◽

Empirical Measures ◽

Climatological Data ◽

Effective Precipitation

Abstract. Recent work suggests that a coupled effective energy and mass transfer (EEMT) term, which includes the energy associated with effective precipitation and primary production, may serve as a robust prediction parameter of critical zone structure and function. However, the models used to estimate EEMT have been solely based on long-term climatological data with little validation using direct empirical measures of energy, water, and carbon balances. Here we compare catchment-scale EEMT estimates generated using two distinct approaches: (1) EEMT modeled using the established methodology based on estimates of monthly effective precipitation and net primary production derived from climatological data, and (2) empirical catchment-scale EEMT estimated using data from 86 catchments of the Model Parameter Estimation Experiment (MOPEX) and MOD17A3 annual net primary production (NPP) product derived from Moderate Resolution Imaging Spectroradiometer (MODIS). Results indicated positive and significant linear correspondence (R2 = 0.75; P < 0.001) between model and empirical measures with an average root mean square error (RMSE) of 4.86 MJ m−2 yr−1. Modeled EEMT values were consistently greater than empirical measures of EEMT. Empirical catchment estimates of the energy associated with effective precipitation (EPPT) were calculated using a mass balance approach that accounts for water losses to quick surface runoff not accounted for in the climatologically modeled EPPT. Similarly, local controls on primary production such as solar radiation and nutrient limitation were not explicitly included in the climatologically based estimates of energy associated with primary production (EBIO), whereas these were captured in the remotely sensed MODIS NPP data. These differences likely explain the greater estimate of modeled EEMT relative to the empirical measures. There was significant positive correlation between catchment aridity and the fraction of EEMT partitioned into EBIO (FBIO), with an increase in FBIO as a fraction of the total as aridity increases and percentage of catchment woody plant cover decreases. In summary, the data indicated strong correspondence between model and empirical measures of EEMT with limited bias that agree well with other empirical measures of catchment energy and water partitioning and plant cover.

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Thermodynamic constraints on effective energy and mass transfer and catchment function

Hydrology and Earth System Sciences Discussions ◽

10.5194/hessd-8-7319-2011 ◽

2011 ◽

Vol 8 (4) ◽

pp. 7319-7354 ◽

Cited By ~ 3

Author(s):

C. Rasmussen

Keyword(s):

Mass Transfer ◽

Vapor Pressure ◽

Primary Production ◽

Vapor Pressure Deficit ◽

Critical Zone ◽

Effective Energy ◽

State Variables ◽

Empirical Measures ◽

Effective Precipitation ◽

Catchment Function

Abstract. Understanding how water, energy and carbon are partitioned to primary production and effective precipitation is central to quantifying the limits on critical zone evolution. Recent work suggests quantifying energetic transfers to the critical zone in the form of effective precipitation and primary production provides a first order approximation of critical zone process and structural organization. However, explicit linkage of this effective energy and mass transfer (EEMT; W m−2) to critical zone state variables and well defined physical limits remains to be developed. The objective of this work was to place EEMT in the context of thermodynamic state variables of temperature and vapor pressure deficit, with explicit definition of EEMT physical limits using a global climate dataset. The relation of EEMT to empirical measures of catchment function was also examined using a subset of the Model Parameter Estimation Experiment (MOPEX) catchments. The data demonstrated three physical limits for EEMT: (i) an absolute vapor pressure deficit threshold of 1200 Pa above which EEMT is zero; (ii) a temperature dependent vapor pressure deficit limit following the saturated vapor pressure function up to a temperature of 292 K; and (iii) a minimum precipitation threshold required from EEMT production at temperatures greater than 292 K. Within these limits, EEMT scales directly with precipitation, with increasing conversion of the precipitation to EEMT with increasing temperature. The state-space framework derived here presents a simplified framework with well-defined physical limits that has the potential for directly integrating regional to pedon scale heterogeneity in effective energy and mass transfer relative to critical zone structure and function within a common thermodynamic framework.

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