Differences In Hydrological Response Research Articles

Comparison of hydrological impacts of climate change simulated by six hydrological models in the Dongjiang Basin, South China

Large differences in future climatic scenarios found when different global circulation models (GCMs) are employed have been extensively discussed in the scientific literature. However, differences in hydrological responses to the climatic scenarios resulting from the use of different hydrological models have received much less attention. Therefore, comparing and quantifying such differences are of particular importance for the water resources management of a catchment, a region, a continent, or even the globe. This study investigates potential impacts of human-induced climate change on the water availability in the Dongjiang basin, South China, using six monthly water balance models, namely the Thornthwaite–Mather (TM), Vrije Universitet Brussel (VUB), Xinanjiang (XAJ), Guo (GM), WatBal (WM), and Schaake (SM) models. The study utilizes 29-year long records of monthly streamflow and climate in the Dongjiang basin. The capability of the six models in simulating the present climate water balance components is first evaluated and the results of the models in simulating the impact of the postulated climate change are then analyzed and compared. The results of analysis reveal that (1) all six conceptual models have similar capabilities in reproducing historical water balance components; (2) greater differences in the model results occur when the models are used to simulate the hydrological impact of the postulated climate changes; and (3) a model without a threshold in soil moisture simulation results in greater changes in model-predicted soil moisture with respect to alternative climates than the models with a threshold soil moisture. The study provides insights into the plausible changes in basin hydrology due to climate change, that is, it shows that there can be significant implications for the investigation of response strategies for water supply and flood control due to climate change.

HYDROLOGIC IMPACTS OF LAND-USE CHANGES IN COASTAL PLAIN WATERSHEDS

Conservation programs developed and implemented by the USDA have led to land-use changes of large areasthroughout the U.S. These changes in land-use may lead to changes in evapotranspiration and infiltration and subsequentlyto dramatic differences in hydrologic response. The impact of recent land-use changes was evaluated using observedprecipitation and streamflow data from the Little River watershed in south-central Georgia in the U.S. Land-use patternswithin the watershed were examined through classification of satellite images collected from 1975 to 2003. While somechanges in land-use were determined, analysis of the data indicated that the overall changes were less than the typicalclassification errors obtained. Based on the analysis of the satellite imagery, conservation practices implemented in the LittleRiver watershed have not significantly altered total forest acreage. In addition, 34 years of hydrologic data collected fromthis watershed do not indicate any significant changes in hydrologic patterns. The long-term average ratio of annual flowto annual precipitation for the Little River watershed has remained stable at approximately 0.27. Year-to-year variation ofthe ratio varied from a high of 0.41 observed during a year with above-normal winter rainfall to 0.06 observed during a yearwith very low annual rainfall. When subwatersheds of the Little River were compared, significant differences in theirresponsiveness to rainfall were found. Linear regression between precipitation and streamflow produced regressioncoefficients between 0.62 and 0.90. These differences were attributed to differences in physical characteristics and land-use.Long-term data from the watersheds indicate that streamflow response is dominated by annual and seasonal precipitationcharacteristics.

Discharge Characteristics and Changes over the Ob River Watershed in Siberia

This study analyzes long-term (1936–90) monthly streamflow records for the major subbasins within the Ob River watershed in order to examine discharge changes induced by human activities (particularly reservoirs and agricultural activities) and natural variations. Changes in streamflow pattern were found to be different between the upper and lower parts of the Ob watershed. Over the upper Ob basin, streamflow decreases in summer months and increases in the winter season. The decreases in summer are mainly due to water uses along the river valley for agricultural and industrial purposes and to reservoir regulation to reduce the summer peak floods. The increases in winter streamflow are caused by reservoir impacts to release water for power generation over winter months. In the lower Ob regions, however, streamflow increased during midsummer and winter months and weakly decreased in autumn. These increases in summer flow are associated with increases in summer precipitation and winter snow cover over the northern Ob basin. Because of reservoir regulations and water uses in the upper parts of the Ob basin, it is a great challenge to determine hydrologic response to climate change and variation at the basin scale. Discharge records observed at the Ob basin outlet do not always represent natural changes and variations mainly due to impacts of large dams; they tend to underestimate the natural runoff trends in summer and overestimate the trends in winter and autumn seasons. This study clearly demonstrates regional differences in hydrologic response to climate changes and variations within a large watershed such as the Ob River. It also illustrates that, relative to climatic effects, human activities are sometimes more important and direct in altering regional hydrologic regimes and affecting their long-term changes particularly at both seasonal and regional scales. It is, therefore, necessary to consider human activities in regional/global environment change analyses and further examine their impacts in other large northern watersheds.

Generalized hydraulic geometry: Derivation based on a multiscaling formalism

Relationships between channel characteristics (e.g., mean depth, water surface width, mean velocity) and discharge, known as hydraulic geometry (HG), have been extensively used by hydrologists and geomorphologists since the seminal work of Leopold and Maddock [1953]. On the basis of recent empirical evidence that the parameters of at‐site HG depend systematically on the contributing area (scale) and that the parameters of downstream HG depend on the frequency of discharge, we propose a multiscaling formalism within which to model and interpret both at‐site and downstream HG in a homogeneous region. In particular, we postulate and test multiscaling models for cross‐sectional area and discharge and derive generalized HG relationships that explicitly account for scale‐frequency dependence. The multiscaling formalism is tested in several basins in Oklahoma and Kansas for drainage areas ranging from 2 to 20,000 km2 and shows good agreement with the data. To quantify the effects that scale dependence in HG has on the hydrologic response of a basin, a geomorphologic nonlinear cascade of reservoirs model has been used to compute attributes of a representative hydrologic response function for various levels of catchment‐averaged effective rainfall and different basin orders. The numerical experiment shows substantial differences in hydrologic response when using classical versus generalized HG. Finally, a preliminary effort is reported to generalize even further the HG relationships such that they can account for deviations from a single power law (e.g., consideration of two different power laws in low‐ and high‐flow regimes) through the introduction of a bivariate mixed multiscaling framework.

Predictions in catchment hydrology: an Australian perspective

Throughout Australia, there are strong regional differences in hydrological response to landscape and climate; however, in general terms, in Australian catchments the flows are typically peakier, base flows are of lower proportion, runoff coefficients are smaller, and dry periods are longer and more variable, than in European and North American catchments. In this context, this paper assesses the model types available to improve understanding and prediction of catchment flows and transport. Included in this is the concept of information and its influence on appropriate model complexity, as well as a characterization of the principal factors inhibiting model performance. The ability to predict the effects on flows and water quality of anything but major changes in climate and land use is limited. Improvement of understanding and prediction relies on the following: more rigorous testing of models to assess their ability to separate climate and land use effects on hydrological response; the use and improved interpretation of spatial data; more and better monitoring of hydrological response at a range of scales; complementary use of conceptual and distributed models; and integration of modelling with other information such as that from geochemical studies including tracer analysis.

Runoff and erosion processes and rates in the Zin valley badlands, northern Negev, Israel

AbstractBadland areas are usually regarded as impermeable zones which generate high runoff and are very vulnerable to sheetwash and rainsplash. To test those considerations sprinkling experiments using two rainfall simulators were carried out on slopes of varying aspect in the northern Negev (Israel). For one unit 1·5 m2 plots were used with rainfall of natural characteristics at 36 mm/hr intensity and 43–48 minute duration, runoff being recorded and water/sediment samples taken every 5 minutes. The second unit was used on 30–50 m2 plots but rainfall energy production was below that of natural rainfall. Results show that due to the high stability and strong flocculation of clay‐rich aggregates rainsplash is ineffective in surface sealing so that infiltration capacities remain high despite intense, prolonged rainfall. Aspect differences are reflected in variation of surface properties despite homogenous bed‐rock, which cause marked differences in hydrological response. North‐facing slopes respond more quickly, more frequently and produce more runoff than south‐facing slopes. Non‐uniform runoff generation is also seen within plots of one aspect reflecting subtle variations in surface properties. Comparison of rainfall intensity and duration used during the experiments with those prevailing under natural conditions shows that under present day conditions surface flow in the Zin valley badlands must be extremely infrequent and denudation rates very low.

The hydrological response of headwater and sideslope areas / La réponse hydrologique des zones de cours supérieurs et des zones de pente latérale

Abstract This paper shows that the hydrological response of convergent headwater and divergent sideslope areas, within a broadly homogenous basin, may be expected to be significantly different. A field study of three headwater and two sideslope areas of the order of 0.25 km2 in the Crimple Beck catchment, Yorkshire, England, is described. Spatial variations in gauged rainfall inputs to the sub-basin areas are shown to be small relative to differences in hydrological response. Results from winter and spring storms show that the headwater areas will generally provide significantly higher and earlier peak flows per unit area, and more total storm discharge, than the sideslope areas. Areas of surface saturation of the soil are most commonly found during and between storms in convergent hollow areas associated with ephemeral channels, expanding as variable contributing areas of surface flow during storm rainfall. In this basin, however, there was also a tendency for both headwater and sideslope sub-basins to g...