Improved unit hydrograph identification for seven Welsh rivers: implications for estimating continuous streamflow at ungauged sites
ABSTRACT A unit hydrograph-based continuous rainfall—streamflow model is applied at daily time step to several catchments in Wales. Two calibration methods are compared for seven catchments. Five of the catchments are among 60 basins in England and Wales for which models were derived by other investigators using the first calibration method, in order to devise a regionalization scheme allowing model parameters to be estimated from catchment properties. The paper shows that in several cases the first calibration method tends to overestimate low flows and give a positively biased estimate for one of the unit hydrograph parameters. It also shows that the second parameter calibration method can often overcome this problem, yielding model parameters more suitable for regionalization with respect to physical catchment properties. Implications of the work are discussed in the context of improving regionalization schemes where the estimation of streamflow in ungauged basins is the major objective.
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ABSTRACT: Pollution from agriculture has environmental consequences at local and global scales. Managing this pollution is challenging because of diffuse sources and complex relationships between aquatic and atmospheric emissions. We illustrate this for a UK county that has suffered outbreaks of microbial pollution and eutrophication. We surveyed 49 livestock farms covering 12% of total agricultural grazed land. Soil nutrient status and whole-farm nutrient balances were determined, and the environmental impact of alleviating sub-optimal soil pH by liming was estimated at the county level. Only 37% of fields contained more P than was required for satisfactory grass growth, and soil acidity and available K were often limiting production. The mean farm N, P and K balances were similar to a modelled farm in England & Wales and EU indicators for the majority of North West Europe. This suggests that local eutrophication events linked to agriculture are more likely to relate to improper timing of nutrient application rather than over-application. None of the surveyed farmers used nutrient decision support tools, largely due to a lack of awareness and competing sources of information. Liming soils to pH 6.0 was estimated to both reduce N-leaching and N2O emissions; however, the net climate-change impact would be negative as the direct CO2 emissions would exceed CO2 equivalent emissions of not liming by 394% (95% CI 201–21,232). Although liming currently presents a net cost to farmers, a sensitivity analysis suggests that reduced lime cost could lead to economic benefit to farmers but still increased greenhouse gas emissions. The results are applicable to all pasture-based agricultural systems where there is a drive to maintain or increase production through optimal soil and nutrient management. The findings demonstrate an important trade-off between reducing aquatic and atmospheric pollution and agricultural productivity, and the need to improve communication of this trade-off to farmers.Agriculture Ecosystems & Environment 04/2014; 188:48–56. DOI:10.1016/j.agee.2014.02.016 · 3.20 Impact Factor
- Hydrological Sciences Journal/Journal des Sciences Hydrologiques 12/2005; 50(6):1053-1068. · 1.25 Impact Factor
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ABSTRACT: The performance of a simple, spatially-lumped, rainfall–streamflow model is compared with that of a more complex, spatially-distributed model. In terms of two model-fit statistics it is shown that for two catchments in Brazil (about 30,000 km2 and 34,000 km2) with different flow regimes, the simpler catchment models, which are unit hydrograph-based and require only rainfall, streamflow and air temperature data for calibration, perform about as well as more complex catchment models that require additional information from satellite images and digitized maps of elevation, land-use and soils. Simple catchment models are applied in forecasting mode, using daily rainfall forecasts from a regional weather forecasting model. The value of the rainfall forecasts, relative to the case where rainfall is known, is assessed for both catchments. The results are discussed in the context of on-going work to compare different modelling approaches for many other Brazilian catchments, and to apply improved forecasting algorithms based on the simple modelling approach to the same, and other, catchments.Environmental Modelling and Software 09/2007; 22(9):1229–1239. DOI:10.1016/j.envsoft.2006.07.004 · 4.54 Impact Factor