Estimating leaf area index of the deciduous forest in the Dragonja watershed. Part 2: Results and discussion

Measurements and estimation of leaf area index (LAI) were carried out in the deciduous forest in the experimental watershed of the Dragonja River. At the same time precise measurements and analysis relevant to single elements of the forest hydrological cycle and other vegetational\ud parameters with modern measuring equipment were made. In Part 1 of the paper (Šraj, 2003b) the methods of delineation of the leaf area index and measurements of LAI were discussed. An accurate description of characteristical features of trees on both chosen plots was also given. In this part of the paper, results of measurements, LAI estimation and analysis are given. The measurements\ud commenced in autumn 2000. The specific leaf area (SLA) was estimated for the most abundant tree species (for example oak, ash, hornbeam, maple, cornelian cherry dogwood). Leaf area index was estimated according to three methods: direct method of litterfall collection, method of hemispherical photography, and method of measuring photosynthetically active radiation (PAR). The analyses revealed that the methods of hemispherical photography and of photosynthetically active radiation (PAR) underestimated the value of LAI in the full-leaf period. LAI estimated\ud according to the litterfall collection method was 6.7 on the south plot and 7.3 on the north plot. The lower value of LAI on the south plot was expected, since the forest on the south plot has a more open character than the one on the north plot

Rainfall interception by two deciduous Mediterranean forests of contrasting stature in Slovenia

Measurements of precipitation above the canopy, throughfall and stemflow were\ud made on the south and north-facing slopes of a deciduous forest on the experimental\ud watershed of the Dragonja river in SW Slovenia. The Dragonja watershed was\ud chosen for the experimental watershed, being of interest because of intensive natural\ud reforestation in the last decades that caused a decrease in minimum and maximum\ud flows. At the same time no noticeable precipitation and temperature changes were\ud observed. Two forest plots were selected. One is located on the north-facing slope\ud (1419 m2) and the other on the south-facing slope (615 m2). Analyses and modelling\ud were made for a one-year period from October 2000 to September 2001. The leaf\ud area index (LAI) was estimated by three methods, one direct and two indirect ones.\ud The obtained values of LAI with the direct method were 6.6 and 6.9 for the south and\ud north slopes, respectively. Measurements and regression analyses gave the mean\ud annual throughfall value (± standard error) on the south plot 67.1 (± 9.6) % of gross\ud precipitation, and 71.5 (± 11.6) % on the north plot. The average stemflow values\ud were 4.5 (± 0.8) % of gross precipitation in the south plot and 2.9 (± 0.6) % in the\ud north plot. The average annual interception losses amount to 28.4 (± 4.1) and 25.4 (±\ud 4.0) % for the south and north slopes, respectively. In the study a significant influence\ud of the south-east wind was proven. With regression analyses and the classification\ud decision tree model it was established that at the events with more than 7 mm of\ud precipitation and south-east wind with a speed higher than 4 m/s an unusually low\ud amount of throughfall occurred and thus high interception losses. The analytical\ud Gash model of rainfall interception (Gash, 1979; Gash et al., 1995) was successfully\ud applied. The results of the modelling corresponded well to the observed values and\ud were within the limits of the standard error of the observed values

The influence of effective rainfall on modeled runoff hydrograph

Influence of the pattern of effective rainfall on modeled hydrograph was investigated in the study. The\ud modelling was performed with the U.S. Army Corps of Engineers hydrograph package HEC-HMS 3.2 and\ud calibrated and validated on measured hydrographs of Glinscica watershed. Six different models of rainfall\ud loss were applied and their effect on modeled hydrograph was evaluated. Peak discharge, time of peak\ud discharge and runoff volume were compared. The best results with the lowest RMSE in the study was\ud obtained with the SCS curve number loss method. Also synthetic hyetographs of different probability and\ud duration were used. Three positions of the maximum rainfall intensity at 25, 50 and 75 % of the rainfall\ud duration were applied. The results showed essential differences in simulated time to peak and also\ud differences in peak discharge. The differences in time to peak increases considerably with the increasing of\ud the rainfall duration. Finally, the results of constant intensity distribution of rainfall of different durations\ud were compared with those obtained with typical rainfall distribution with the position of the maximum\ud intensity at 50 %. Results showed considerable differences in peak discharge and time to peak by longer\ud durations of the rainfall

Comprehensive low-flow analysis of the Vipava river

The article presents the results of the analysis of low flows at 5 gauging stations on the Vipava River, which has a Dinaric pluvial-nival regime (catchment area of 590 km2). The low-flow statistics show that the gauging station Vipava stands out with the lowest values. Baseflow index (BFI) values are comparable among the considered stations and are around 0.40. Relatively low BFI values indicate low soil permeability. A high similarity between the mean annual minimum 7-day flow (MAM7) and the 95th percentile exceedance discharge (Q95) at all gauging stations indicates a temperate climate. The highest flows values occur in spring and autumn, and the lowest in summer. In wet years there are relatively large fluctuations in flow, while in dry years the flow consists mainly of baseflow. This is also confirmed with the flow duration curves analysis. The seasonality analysis shows a predominant summer regime with low flows

Izdelava Huffovih krivulj in njihova analiza za izbrane\ud padavinske postaje v Sloveniji

Prispevek predstavlja izdelavo, rezultate in analizo Huffovih krivulj za izbrane meteorološke postaje: Ljubljana, Murska Sobota, Novo Mesto in Portorož. Za meteorološko postajo Ljubljana smo obdelali podatke od leta 1948 do 2010 in za ostale meteorološke postaje od leta 1970 do 2011. Pri primerjavirezultatov smo ugotovili razlike v obliki Huffovih krivulj in tudi vštevilu neviht, ki so ustrezale definiciji neodvisnega padavinskega dogodka. Razlike med postajami so bile dovolj velike, da lahko zaključimo, da ne moremopredpostaviti ene same oblike Huffovih krivulj za celotno Slovenijo, karnarekuje izdelavo Huffovih krivulj tudi za ostale meteorološke postaje

Analysis of the possibility of\ud using the distributed two-dimensional model Flo-2D for hydrological modelling

The paper presents a hydrological model of the Glinščica watershed with the program \ud Flo-2D. The aim of \ud the research was to analyze the applicability of the two-dimensional mathematical model Flo-2D for \ud hydrological modeling and to compare the results with the one-dimensional HEC-HMS model. Flo-2D is \ud a commercial, physically based model with distributed parameters. lts main purpose is \ud modeling river hydraulics. lt continuously computes the rainfall runoff from the watershed according to the \ud topography or a\ud digital elevation model (DEM), the quantity and intensity of precipitation, the land use and soil \ud type. On the other hand, HEC-HMS is freely available software that enables to create a simple and \ud sufficiently detailed hydrologic model on the basis of precipitation, discharge and some watershed \ud characteristics. ln both cases precipitation losses were computed with SCS (Soil Conservation \ud Service) Curve Number loss method. Flo-\ud 2D model was calibrated by varying input and modeling parameters including grid size, roughness \ud coefficients and SCS Curve Numbers. The results of 10-year and 100-year events and 2, 12 and \ud 24-hour storms are also compared. The results of runoff volumes are comparable, but the shape of \ud runoff hydrograph computed with HEC-HMS model is much better. ln the Flo-2D model assessing the \ud Manning roughness coefficient and selecting the size of the grid cells are the most problematic, \ud whereas in the HEC-HMS model it is the assessment of the time of concentration. Calibration of the \ud model with distributed parameters is difficult and time-consuming. The results have shown that the \ud Flo-2D model can be used in hydrological\ud practice only in cases where good input data are available for the model and its calibration.\u

Measurements and Analysis of Intercepted Precipitation of Silver Birch (Betula pendula Roth.) and Scots Pine (Pinus sylvestris L.) in Urban Area

Study presents measurements, comparation and analysis of intercepted precipitation of\ud coniferous and deciduous trees. Measurements were made on experimental plot in the urban\ud part of the city Ljubljana on two groups of trees: Betula pendula and Pinus sylvestris.\ud Analyses and comparations of throughfall and stemflow were made for the period from June\ud 2004 till December 2006 which was devided onto four vegetation periods. Rainfall above the\ud canopy was measured automatically with a tipping bucket rain gauge with digital recording of\ud results every 10 minutes in combination with manual Helman's rain gauge for control.\ud Throughfall was measured using a combination of fixed gauges with digital recording of\ud results every 10 minutes and manual roving gauges. Stemflow was measured manually on one\ud tree of each specie. The results of the measurements showed that the throughfall for Betula\ud pendula was 57-70 % of precipitation and for Pinus sylvestris 35-49 % which is comparable\ud with the results of other similar studies around the world. The stemflow fraction for Betula\ud pendula amounted 1,1-6,7 % of precipitation and it was practically negligible for Pinus\ud sylvestris

Drought Analysis Using the Standardized Precipitation Index (SPI)

Drought indices are commonly used for detection, monitoring and evaluation of drought events. One of the most commonly used drought indices is the Standardized Precipitation Index (SPI). This paper presents the effect of theoretical distribution selection on SPI values, and the analysis of drought events for five selected meteorological stations in Slovenia. We found that the SPI on the annual time scale shows a similar pattern of occurrence of dry and wet periods at Ljubljana-Bežigrad, Novo mesto, and Trieste meteorological stations; something similar can be said for the Celje and Maribor-Tabor stations. The analysis of the correlations between the standardized data river discharge and precipitation data for the selected river basin of the River Pesnica shows the strongest correlation between the SPI-2 and standardized discharges

The influence of climate change on discharge fluctuations in Slovenian rivers

In recent decades, an increase in the number of extreme flood events as well as extreme drought events has been observed in Slovenia. This rise the need for a comprehensive analysis of trends in discharge data series. In the study, statistical trends in seasonal and annual mean, maximum, extreme and low discharge values were investigated using the Mann Kendall test. The results show a temporal and spatial variability of trends in discharge. In general, a decreasing trend in water quantities in the rivers was observed. However, results at some gauging stations indicate statistically significant increasing trends, especially for maximum and extreme discharges. Additional analyses show that the discharge trends depend on the location of the gauging station

Design Rainfall in Engineering Applications with Focus on the Design Discharge

Design hyetograph or design storm definition is one of the most important parts of the design discharge determination in case of ungauged catchments. Design hyetograph duration and temporal rainfall distribution can have large impact on the peak discharge values and the shape of the runoff hydrograph. The influence of these two factors on the design runoff values is presented in the case study of the Glinščica River catchment that covers 16.85 km2 and it is located in central part of Slovenia, Europe. A combination of Huff and intensity-duration-frequency (IDF) curves is used to construct the design hyetograph for the presented case study. The duration of the design storm is determined by the catchment time of concentration. The results are compared to the Natural Resources Conservation Service (NRCS) curves and the so-called frequency storm method. The hydrological modeling result that was carried out using the hydrologic modeling system (HEC-HMS) software indicates that differences among different methods should not be neglected. For the 10-year return period, differences in the peak discharge values can be larger than 10%, while even larger differences can be expected for longer return periods. Some studies showed that these can be larger than 50%. Therefore, the guidelines on how to construct the design hyetograph are presented