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Hydrological Balance (hydrological + balance)
Selected AbstractsAtmospheric moisture budget over Antarctica and the Southern Ocean based on the ERA-40 reanalysisINTERNATIONAL JOURNAL OF CLIMATOLOGY, Issue 15 2008Hanna Tietäväinen Abstract The atmospheric moisture budget over Antarctica and the Southern Ocean was analysed for the period 1979,2001 on the basis of the ERA-40 reanalysis of the European Centre for Medium-Range Weather Forecasts. Meridional transport by transient eddies makes the largest contribution to the southward water vapour transport. The mean meridional circulation contributes to the northward transport in the Antarctic coastal areas, but this effect is compensated by the southward transport by stationary eddies. The convergence of meridional water vapour transport is at its largest at 64,68°S, while the convergence of zonal transport is regionally important in areas of high cyclolysis. Inter-annual variations in water vapour transport are related to the southern annular mode (SAM). The eastward transport has a significant (95% confidence level) positive correlation with the SAM index, while the northward transport has a significant negative correlation with SAM near 60°S. Hydrological balance is well-achieved in the ERA-40 reanalysis: the difference between the water vapour flux convergence (based on analysis) and the net precipitation (precipitation minus evaporation, based on 24-h forecasts) is only 13 mm yr,1 (3%) over the Southern Ocean and , 8 mm yr,1 (5%) over the continental ice sheet. Over the open ocean, the analysis methodology favours the accuracy of the flux convergence. For the whole study region, the annual mean flux convergence exceeded net precipitation by 11 mm yr,1 (3%). The ERA-40 result for the mean precipitation over the Antarctic continental ice sheet in 1979,2001 is 177 ± 8 mm yr,1, while previous estimates range from 173 to 215 mm yr,1. For the period 1979,2001, the ERA-40 data do not show any statistically significant trend in precipitation over the Antarctic grounded ice sheet and ice shelves. From the ERA-40 data, the annual average net evaporation (evaporation minus condensation) is positive over the whole continent. Copyright © 2008 Royal Meteorological Society [source] Rainfall variability and hydrological and erosive response of an olive tree microcatchment under no-tillage with a spontaneous grass cover in SpainEARTH SURFACE PROCESSES AND LANDFORMS, Issue 7 2010E. V. Taguas Abstract Most studies on runoff and soil loss from olive orchards were performed on plots, despite the fact that measurements that examine a range of erosive processes on different scales are essential to evaluate the suitability of the use and soil management of this type of land. The main environmental limitations of much of the land used for olive orchards in the Mediterranean are the steep slopes and the shallow soil depth , and this was the case in the study area. Soil erosion and runoff over two hydrological years (2005,2006 and 2006,2007) were monitored in an olive orchard microcatchment of 6·1,ha under no-tillage with spontaneous grass in order to evaluate its hydrological and erosive behaviour. Moreover, soil parameters such as organic matter (%OM), bulk density (BD) and hydraulic saturated conductivity (Ks) were also examined in the microcatchment to describe management effects on hydrological balance and on erosive processes. In the study period, the results showed runoff coefficients of 6·0% in the first year and 0·9% in the second. The differences respond to the impact of two or three yearly maximum events which were decisive in the annual balances. On the event scale, although maximum rainfall intensity values had a big influence on peak flows and runoff, its importance on mean sediment concentrations and sediment discharges was difficult to interpret due to the likely control of grass cover on volume runoff and on soil protection. In the case of annual soil erosion, they were measured as 1·0,Mg,ha,1,yr,1 and 0·3,Mg,ha,1,yr,1. Both are lower than the tolerance values evaluated in Andalusia (Spain). These results support the implementation of no-tillage with spontaneous grass cover for sloping land, although the reduced infiltration conditions determined by Ks in the first horizon suggest grass should be allowed to grow not only in spring but also in autumn. In addition, specific measurements to control gullies, which have formed in the terraced area in the catchment, should be included since it is expected that they could be the main sources of sediments. Copyright © 2010 John Wiley & Sons, Ltd. [source] The Role of Surface Water Drainage in Environmental Change: a Case Example of the Upper South East of South Australia; an Historical ReviewGEOGRAPHICAL RESEARCH, Issue 3 2001Kathryn H. Taffs The role of surface water drainage in environmental change in Australia is rarely appreciated. Drains can modify surface water hydrology, not only altering flow regimes but also rapidly dispersing contaminants and altering the natural hydrological balance of associated flora and fauna. Yet drainage continues to be considered a viable management strategy rather than as a cause of land degradation. The impact of surface water drainage in an inherently saline area of South Australia, the Upper South East, is investigated. Surface water drains were constructed by developers in an attempt to increase the area of land available and viable for agricultural land use. Drainage strategies altered the natural direction, magnitude and frequency of surface water flow. The Upper South East has experienced periods of both increased surface water and flooding, and surface water deficit, in the past one hundred years. The region now receives less surface water than under pre-European conditions, but local runoff is channelled into and through the wetlands more rapidly than before European settlement. Future management strategies are likely to continue this trend, to the detriment of remnant natural wetlands. [source] Modelling lake stage and water balance of Lake Tana, EthiopiaHYDROLOGICAL PROCESSES, Issue 25 2009Yirgalem A. Chebud Abstract The level of Lake Tana, Ethiopia, fluctuates annually and seasonally following the patterns of changes in precipitation. In this study, a mass balance approach is used to estimate the hydrological balance of the lake. Water influx from four major rivers, subsurface inflow from the floodplains, precipitation, outflow from the lake constituting river discharge and evapotranspiration from the lake are analysed on monthly and annual bases. Spatial interpolation of precipitation using rain gauge data was conducted using kriging. Outflow from the lake was identified as the evaporation from the lake's surface as well as discharge at the outlet where the Blue Nile commences. Groundwater inflow is estimated using MODular three-dimensional finite-difference ground-water FLOW model software that showed an aligned flow pattern to the river channels. The groundwater outflow is considered negligible based on the secondary sources that confirmed the absence of lake water geochemical mixing outside of the basin. Evaporation is estimated using Penman's, Meyer's and Thornwaite's methods to compare the mass balance and energy balance approaches. Meteorological data, satellite images and temperature perturbation simulations from Global Historical Climate Network of National Oceanographic and Atmospheric Administration are employed for estimation of evaporation input parameters. The difference of the inflow and outflow was taken as storage in depth and compared with the measured water level fluctuations. The study has shown that the monthly and annually calculated lake level replicates the observed values with root mean square error value of 0·17 and 0·15 m, respectively. Copyright © 2009 John Wiley & Sons, Ltd. [source] | ||||||||||