János Józsa

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.

MODIS-aided statewide net groundwater-recharge estimation in Nebraska.

Monthly evapotranspiration (ET) rates (2000 to 2009) across Nebraska at about 1-km resolution were obtained by linear transformations of the MODIS (MODerate resolution Imaging Spectroradiometer) daytime surface temperature values with the help of the Priestley-Taylor equation and the complementary relationship of evaporation. For positive values of the mean annual precipitation and ET differences, the mean annual net recharge was found by an additional multiplication of the power-function-transformed groundwater vulnerability DRASTIC-code values. Statewide mean annual net recharge became about 29 mm (i.e., 5% of mean annual precipitation) with the largest recharge rates (in excess of 100 mm/year) found in the eastern Sand Hills and eastern Nebraska. Areas with the largest negative net recharge rates caused by declining groundwater levels due to large-scale irrigation are found in the south-western region of the state. Error bounds of the estimated values are within 10% to 15% of the corresponding precipitation rates and the estimated net recharge rates are sensitive to errors in the precipitation and ET values. This study largely confirms earlier base-flow analysis-based statewide groundwater recharge estimates when considerations are made for differences in the recharge definitions. The current approach not only provides better spatial resolution than available earlier studies for the region but also quantifies negative net recharge rates that become especially important in numerical modeling of shallow groundwater systems.

Remote-Sensing Based Groundwater Recharge Estimates in the Danube-Tisza Sand Plateau Region of Hungary

Remote-Sensing Based Groundwater Recharge Estimates in the Danube-Tisza Sand Plateau Region of Hungary Mean annual recharge in the Danube-Tisza sand plateau region of Hungary over the 2000-2008 period was estimated at a 1-km spatial resolution as the difference of mean annual precipitation (P) and evapotranspiration (ET). The ET rates were derived from linear transformations of the MODIS daytime land surface temperature (Ts) values with the help of ancillary atmospheric data (air temperature, humidity, and sunshine duration). The groundwater under the sand plateau receives about 75 ± 50 mm of recharge annually (the plus/minus value is the associated error, resulting from an assumed 5% error in both the P and ET values), which is about 14 ± 9 % of the regional mean annual P value of 550 mm. The largest continuous region with elevated recharge rates (about 180 ± 50 mm a-1 or 30 ± 8 % of P) occur in the south-western part of the plateau due to more abundant precipitation (around 580 mm a-1), while recharge is the smallest (about 40 ± 40 mm a-1 or 7 ± 7 % of P) under forested areas. Typically, lakes, wetlands, river valleys, and certain afforested areas in the north-central part of the region act as discharge areas for groundwater. Doplňovanie Podzemných Vôd Piesočnatej Plošiny Medzi Riekami Dunaj A Tisa, Určené Z Údajov Diaľkového Prieskumu Priemerný ročný úhrn doplňovania podzemných vôd plošiny zloženej z pieskov medzi riekami Dunaj a Tisa s rozlíšením 1 km, pre roky 2000-2008 bol určený ako rozdiel medzi priemerným ročným úhrnom zrážok (P) a evapotranspiráciou (ET). ET bolo určené z lineárnej transformácie teploty povrchu počas dňa (Ts) získanej systémom MODIS pomocou údajov o vlastnostiach atmosféry (teplota vzduchu, vlhkosť vzduchu a trvanie slnečného svitu). Podzemná voda pod pieskovým masívom dostáva ročne asi 75 ± 50 mm vody (znamienka plus/mínus znamenajú chybu, vyplývajúcu z predpokladanej 5% chyby hodnôt P a ET), ktorá je asi 14 ± 9 % regionálnej priemernej ročnej hodnoty P, ktorá je 550 mm. Najväčšia spojitá oblasť so zvýšeným doplňovaním podzemnej vody (približne 180 ± 50 mm za rok alebo 30 ± 8 % P) sa nachádza v juhozápadnej časti plató a je dôsledkom vyššieho ročného úhrnu zrážok (okolo 580 mm), doplňovanie je nižšie v zalesnených oblastiach (okolo 40 ± 40 mm, alebo 7 ± 7 % P). Jazerá, mokrade, rieky a niektoré zalesnené oblasti v strednej a severnej časti tejto oblasti drénujú podzemné vody.

Estimation of Suspended Sediment Concentrations with Adcp in Danube River

Abstract An estimation procedure for suspended sediment concentrations based on the intensity of backscattered sound of acoustic Doppler current profilers (ADCP) is introduced in this paper. Based on detailed moving and fixed boat ADCP measurements with concurrent sediment sampling, we have successfully calibrated the estimation method for a reach of River Danube in Hungary, characterized by significant suspended sediment transport. The effect of measurement uncertainty and various data filtering on sediment load determination is also analyzed and quantified. Some of the physical model parameters describing the propagation of sound in water are estimated based on known empirical formulas, while other parameters are derived from measured. Regression analysis is used to obtain a relationship between the intensity of backscattered sound and sediment concentrations. The empirical relationship has been then used to estimate the suspended sediment concentrations from the ADCP data collected in fixed and moving boat measurement operation mode, along verticals and path-lines, respectively. We show that while some measurement uncertainty is inherent to the acoustic Doppler principle, it is further enhanced by the complexity of the near-bottom sediment-laden flow. This uncertainty has then a significant effect on the local sediment load estimation. In turn, reasonable smoothing of raw velocity and backscatter intensity data shows insignificant impact on cross-sectional sediment load estimation.

A Calibration-Free Evapotranspiration Mapping (CREMAP) Technique

Obtaining spatially distributed accurate evapotranspiration (ET) estimates is crucial in most water balance calculations for the identification of mass and energy fluxes across the area of interest. While routine Bowen-ratio or eddy-covariance measurements of sensible and latent heat fluxes are typically representative of a horizontal scale of a few hundred meters (i.e., the so-called plotor field-scale), many hydrologic models work at regional to continental to global scales. Rather than aggregating from the field scale, which may be difficult not only from a theoretical point of view but also from a practical one when long time-periods (years or decades) and large areas are considered, an ET-estimation technique that directly works at the regional scale, yet, at the same time, spatially distributed may be of high practical value. An ET estimation method had been proposed by Bouchet (1963) almost half a century ago, now called the complementary relationship (CR) of evaporation which was subsequently formulated for practical regional-scale applications by Brutsaert & Stricker (1979), and Morton et al. (1985). The CR states that under constant available energy at the surface (Qn) actual (E) and potential (Ep) evapotranspiration rates are complementary, their sum yielding twice the wet-environment (Ew) evapotranspiration rate, provided Ep is obtained by the Penman (1948) equation (Szilagyi & Jozsa, 2009a) and Ew by the Priestley-Taylor equation (Priestley & Taylor, 1972). In other words

On the internal boundary layer related wind stress curl and its role in generating shallow lake circulations

Abstract The paper demonstrates that the wind stress curl as an external vorticity source plays an important role in shaping large scale shallow lake circulations. The analysis of purpose-oriented simultaneous wind and current measurements data from the Hungarian part of Lake Neusiedl reasonably fits well the internal boundary layer development theory over the lake surface. A 2-D vorticity formulation of wind-induced flows is used to demonstrate mathematically the IBL-related large scale circulation generation mechanism well reflected in the measured data. Further validation of the findings is carried out by means of simple 2-D numerical flow modelling, in which details on the flow pattern besides the measurement sites could be also revealed. Wind-induced lake circulations linked to IBL development shows a novelty to be implemented in up-to-date numerical flow models.

Variable density bore interaction with block obstacles

A horizontally variable density flow model is used to simulate hydraulic bore interactions with idealised urban obstacles. The 2D non-linear shallow water equations are solved using a second-order Monotonic Upstream-centered Schemes for Conservation Laws-Hancock Godunov-type HLLC approximate Riemann scheme. Validation test results are reported for wave propagation over a hump, a constant-density circular dam break and two 1D dam breaks involving different spatial distributions of solute concentration. Detailed parameter studies are then considered for hydraulic bore interactions with single and multiple-square obstacles under subcritical, critical and supercritical flow conditions. In all cases, reflected and diffracted wave patterns are generated immediately after the bore impacts the obstacle(s). Later, the incident bore reconstitutes itself downstream of the obstacle(s). Variable density flows are also considered, with the upstream volumetric concentrations set to values corresponding to water–sediment mixture densities of 1165 and 1495 kg/m3. It is found that the upstream Froude number, gap spacing between obstacles and upstream to downstream density difference influence the strength of the bore–structure interaction, run-up at the front face of the obstacle(s), and subsequent wave–wave interactions.

Evapotranspiration Trends (1979–2015) in the Central Valley of California, USA: Contrasting Tendencies During 1981–2007

Trends in monthly evapotranspiration (ET) rates across three watersheds covering the Central Valley in California were calculated by the latest calibration-free version of the complementary relationship of evaporation for 1979–2015. While a recent study concluded that ET rates of the irrigated fields in the Central Valley were declining in 1981–2007, here an ET trend of about 2.6 ± 12 mm per decade was found over the same period in spite of a drop in precipitation ( 22 ± 30 mm per decade) and ET rates ( 9.5 ± 10 mm per decade) for the rest of the watersheds, none of them statistically significant. After 2007, the precipitation decline accelerated causing a sharp drop in both irrigated and nonirrigated ET rates across the watersheds. Observations from the California Irrigation Management Information System support the present findings: Under increasing air temperatures, both dew point temperature and relative humidity values increased (at a statistically significant rate) during 1983–2007, while they reversed afterwards, in agreement with the estimated sharp irrigation ET trend decline for the remainder of the study period. Actual (in this case over irrigated fields) and reference ET rates complement each other, that is, they express opposite tendencies, as was demonstrated with California Irrigation Management Information System data, yielding a statistically significant plot-scale irrigation ET rate increase of 31 to 41 (±17) millimeters per decade for 1983–2007 in accordance with a similar drop in reference ET rates of 28 to 50 (±16) millimeters per decade, depending on whether published monthly or daily values (aggregated to monthly ones after leaving out spurious measurements) were employed.

Habitat mapping of riverine fish by means of hydromorphological tools: Habitat mapping of riverine fish by means of hydromorphological tools

Department of Hydraulic and Water Resources Engineering, Budapest University of Technology and Economics, Budapest, Hungary MTA‐BME Water Management Research Group, Budapest, Hungary MTA Centre for Ecological Research, Danube Research Institute, Budapest, Hungary Duna‐Ipoly National Park Directorate, Budapest, Hungary MTA Centre for Ecological Research, Balaton Limnological Institute, Tihany, Hungary Correspondence Sándor Baranya, Budapest University of Technology and Economics, Department of Hydraulic and Water Resources Engineering, Műegyetem rkp. 3, Budapest 1111, Hungary. Email: baranya.sandor@epito.bme.hu

Wind profile and shear stress at reed-open water interface – recent research achievements in Lake Fertő

The effect of emergent aquatic canopy on over-lake wind field was investigated through detailed field measurements. The aerodynamic roughness length above reed canopy and above open water was determined from eddy-covariance data. It was found that the aerodynamic roughness length at short fetches could be more sufficiently estimated from wave age relations than from the logarithmical profile formula, indicating that near the canopy wind profile might deviate from the theoretical logarithmical form. The presented calculations lead to an improved understanding of the wind profile realignment and wind shear stress development at the interface of the characteristic lake zones, also enhancing the accuracy of the modeling of various wind-induced processes.