Jozsef Szilagyi

Recession flow analysis for aquifer parameter determination

The recession flow analysis of Brutsaert and Nieber (1977) extended by Troch et al. (1993) to estimate aquifer parameters (saturated hydraulic conductivity and mean aquifer depth) is examined by means of a numerical model. It is found to be reliable for the estimation of the catchment-scale saturated hydraulic conductivity and mean aquifer depth. Increasing the complexity of the synthetic watershed had no impact on the accuracy of the estimated parameters.

Baseflow separation based on analytical solutions of the Boussinesq equation

A technique for baseflow separation is presented based on similarity solutions of the Boussinesq equation. The method makes use of the simplifying assumptions that a horizontal impermeable layer underlies a Dupuit aquifer which is drained by a fully penetrating stream. The value of the baseflow maximum as well as the baseflow recession hydrograph can be estimated by fitting the analytical solutions of the Boussinesq equation to the observed discharge values for individual flood events. For the rising limb of the baseflow hydrograph a linear function is assumed for simplicity. The method is first demonstrated on three watersheds for a total of five flood events and extensively applied over a three year period for the Mahantango Creek, Pennsylvania watershed. The proposed method reduces some of the subjective aspects long associated with baseflow separation techniques.

On the inherent asymmetric nature of the complementary relationship of evaporation

[1] New theoretical considerations indicate that the complementary relationship (CR) of evaporation is inherently asymmetric when the time rate of change between actual and apparent potential evaporations is considered. The theory also estimates the extent of this asymmetry as a function of the surface temperature and predicts that a symmetric CR, independent of the surface temperature, can only be expected when no energy exchange between the source of the apparent potential evaporation process and its surroundings occurs, a rather unrealistic situation. The derived asymmetric CR is employed for operational evaporation estimations. The parameters of the proposed practical evaporation estimation model are from the Priestley-Taylor and Penman equations. Citation: Szilagyi, J. (2007), On the inherent asymmetric nature of the complementary relationship of evaporation, Geophys. Res. Lett., 34, L02405, doi:10.1029/ 2006GL028708.

Sudden drawdown and drainage of a horizontal aquifer

Drainage of a saturated horizontal aquifer following a sudden drawdown is reanalyzed using the Boussinesq equation. The effect of the finite length of the aquifer is considered in detail. An analytical approximation based on a superposition principle yields a very good estimate of the outflow when compared to accurate numerical solutions. An illustration of the new analytical approach to analyze basin-scale field data is used to demonstrate possible field applications of the new solution.

Modified Advection-Aridity Model of Evapotranspiration

The original and modified versions of the advection-aridity (AA) model of regional evapotranspiration are tested with data from the Solar and Meteorological Surface Observation Network (SAMSON). The resulting long-term mean annual evapotranspiration estimates are validated against water balances of 25 watersheds that are minimally affected by human activity and contain at least one SAMSON station, as well as with similar closures of SAMSON-station/gridded precipitation and runoff. In general, model performance is very similar among the two versions, explaining at least 80% of the spatial variance in the long-term means, simultaneously remaining well within 10% of the water balance-based values in their station-averaged long-term mean annual evapotranspiration estimates. The modified AA model, however, can be used in humid as well as in arid regions with the same set of calibrated parameters, whereas the original AA model may require a recalibration.

NDVI relationship to monthly evaporation

Note: 25(10): 1753-1756 Reference EFLUM-ARTICLE-1998-006doi:10.1029/98GL01176 Record created on 2005-09-08, modified on 2017-02-23

On Bouchet's complementary hypothesis

Abstract Mortons proof of Bouchets complementary hypothesis has been revisited. The proofs central assumption is that an increase in sensible heat from the surface to the air induces a similar increment in the sensible heat transfer from the air to a hypothetical potential evaporimeter. It is shown that this assumption is not necessary in the derivation. Instead, the complementary hypothesis under simplified conditions can be obtained with the help of the mass conservation equation for water vapor.

Evaluating the complementary relationship of evapotranspiration in the alpine steppe of the Tibetan Plateau

The complementary relationship (CR) of evapotranspiration allows the estimation of the actual evapotranspiration rate (ETa) of the land surface using only routine meteorological data, which is of great importance in the Tibetan Plateau (TP) due to its sparse observation network. With the highest in situ automatic climate observation system in a typical semiarid alpine steppe region of the TP, the wind function of Penman was replaced by one based on the Monin-Obukhov Similarity theory for calculating the potential evapotranspiration rate (ETp); the Priestley-Taylor coefficient, α, was estimated using observations in wet days; and the slope of the saturation vapor pressure curve was evaluated at an estimate of the wet surface temperature, provided the latter was smaller than the actual air temperature. A symmetric CR was obtained between the observed daily actual and potential evapotranspiration. Local calibration of the parameter value (in this order) is key to obtaining a symmetric CR: α, wet environment air temperature (Twea), and wind function. Also, present symmetric CR contradicts previous research that used default parameter values for claiming an asymmetric CR in arid and semiarid regions of the TP. The effectiveness of estimating the daily ETa via symmetric CR was greatly improved when local calibrations were implemented. At the same time, an asymmetric CR was found between the observed daily ETa and pan evaporation rates (Epan), both for D20 aboveground and E601B sunken pans. The daily ETa could also be estimated by coupling the Epan of D20 aboveground and/or E601B sunken pan through CR. The former provided good descriptors for observed ETa, while the latter still tended to overestimate it to some extent.

A geomorphology-based semi-distributed watershed model

A semi-distributed watershed model was developed that conceptualizes the catchment as a cascade of nonlinear storage elements whose geometric dimensions are derived from the Horton‐Strahler ordering of the stream network. Each storage element represents quick storm runoA over land or in a channel segment. The physically based groundwater submodel is parameterized through the application of the Brutsaert‐Nieber recession flow analysis and it provides continuous baseflow separation. The model requires the calibration of seven parameters from a one year rainfall‐runoA record. It was tested on the Mahantango Creek watershed in the Susquehanna River basin, Pennsylvania. ” 1999 Elsevier Science Ltd. All rights reserved.

An objective method for determining principal time scales of coherent eddy structures using orthonormal wavelets

A new, parameter-free method, based on orthonormal wavelet expansions is proposed for calculating the principal time scale of coherent structures in atmospheric surface layer measurements. These organized events play an important role in the exchange of heat, mass, and momentum between the land and the atmosphere. This global technique decomposes the energy contribution at each scale into organized and random eddy motion. The method is demonstrated on vertical wind velocity measurements above bare and vegetated surfaces. It is found to give nearly identical results to a local thresholding approach developed for signal de-noising that assigns the wavelet coefficients to organized and random motion. The effect of applying anti- and/or near-symmetrical wavelet basis functions is also investigated.