Dams on Mekong tributaries as significant contributors of hydrological alterations to the Tonle Sap Floodplain in Cambodia
Summary: Hydrological modeling and assessment tools were used to provide evidence of the expected hydrological alterations that hydropower development in the lower Mekong tributaries could bring to the Tonle Sap. The most significant alterations are in terms of water levels during the dry season and rates of water level rise/drop which are crucial for tree seed germination and fish migrations, and therefore major ecological disruptions are likely to follow.
Relations between macropore network characteristics and the degree of preferential solute transport
Summary: The characteristics of the macropore network determine the potential for fast transport of solutes through soil. Such characteristics computed from 3-dimensional X-ray tomography images were combined with measured solute breakthrough curves and near-saturated hydraulic conductivities. At a given flow rate, smaller macroporosities, poorer local connectivity of the macropore network and smaller near-saturated hydraulic conductivities resulted in a greater degree of preferential transport.
Assessing winter cover crop nutrient uptake efficiency using a water quality simulation model
Summary: This study demonstrates the effectiveness of winter cover crops for reducing nitrate loads using the Soil and Water Assessment Tool (SWAT). It illustrates the following: (1) nitrate removal efficiency varies greatly by species, timing, and extent of winter cover crop implementation; and (2) nitrate exports vary based on edaphic and agronomic characteristics of the croplands upon which crops are planted.
Agro-hydrology and multi-temporal high-resolution remote sensing: toward an explicit spatial processes calibration
Summary: A set of high spatial and temporal satellite images have been used to spatially calibrate crop growth within an agro-hydrological model dedicated to nitrogen contamination of stream water. This type of spatial calibration greatly improved the simulation of nitrogen plant uptake and better constrained nutrient fluxes in the river. This is an example of the benefit of the forthcoming Sentinel-2 high resolution optical image series that will be acquired every 4/5 days over continental surfaces.
S. Ferrant, S. Gascoin, A. Veloso, J. Salmon-Monviola, M. Claverie, V. Rivalland, G. Dedieu, V. Demarez, E. Ceschia, J.-L. Probst, P. Durand, and V. Bustillo Hydrol. Earth Syst. Sci., 18, 5219-5237, 2014 AbstractFinal Revised Paper (PDF, 7033 KB)Supplement (1074 KB)Discussion Paper (HESSD)
16 Dec 2014
Quantification of hydrologic impacts of climate change in a Mediterranean basin in Sardinia, Italy, through high-resolution simulations
Summary: We quantified the hydrologic impacts of climate change in the Rio Mannu basin (472.5 km2), Sardinia, Italy.
We created high-resolution climate forcings for a physically based distributed hydrologic model by combining four climate models with two statistical downscaling tools of precipitation and potential evapotranspiration. A significant diminution of mean annual runoff at the basin outlet (mean of -32%), and a reduction of soil water content and actual evapotranspiration are expected.
Meltwater run-off from Haig Glacier, Canadian Rocky Mountains, 2002–2013
Summary: This paper presents a new 12-year glacier meteorological, mass balance, and run-off record from the Canadian Rocky Mountains. This provides insight into the glaciohydrological regime of the Rockies. For the period 2002-2013, about 60% of glacier meltwater run-off originated from seasonal snow and 40% was derived from glacier ice and firn. Ice and firn run-off is concentrated in the months of August and September, at which time it contributes significantly to regional-scale water resources.
Technical Note: Reducing the spin-up time of integrated surface water–groundwater models
Summary: A new hybrid approach was developed to reduce the computational burden of the spin-up procedure by using a combination of model simulations and an empirical depth-to-water table function. Results illustrate that the hybrid approach reduced the spin-up period required for an integrated groundwater--surface water--land surface model (ParFlow.CLM) by up to 50%. The methodology is applicable to other coupled or integrated modeling frameworks when initialization from an equilibrium state is required.
Analyzing runoff processes through conceptual hydrological modeling in the Upper Blue Nile Basin, Ethiopia
Summary: In this study, topography is considered as a proxy for the variability of most of the catchment characteristics. The model study suggests that classifying the catchments into different runoff production areas based on topography and including the impermeable rocky areas separately in the modeling process mimics the rainfall–runoff process in the Upper Blue Nile basin well and yields a useful result for operational management of water resources in this data-scarce region.
M. Dessie, N. E. C. Verhoest, V. R. N. Pauwels, T. Admasu, J. Poesen, E. Adgo, J. Deckers, and J. Nyssen Hydrol. Earth Syst. Sci., 18, 5149-5167, 2014 AbstractFinal Revised Paper (PDF, 8106 KB)Discussion Paper (HESSD)
12 Dec 2014
Flow pathways and nutrient transport mechanisms drive hydrochemical sensitivity to climate change across catchments with different geology and topography
Summary: We projected potential hydrochemical responses in four neighbouring catchments to a range of future climates. The highly variable responses in streamflow and total phosphorus (TP) were governed by geology and flow pathways, where larger catchment responses were proportional to greater soil clay content. This suggests clay content might be used as an indicator of catchment sensitivity to climate change, and highlights the need for catchment-specific management plans.
Residence times and mixing of water in river banks: implications for recharge and groundwater–surface water exchange
Summary: Periodic flooding of rivers should result in increased groundwater recharge near rivers and thus - younger and fresher groundwater near rivers. This study found the age and salinity of shallow groundwater to increase with proximity to the Tambo River in South East Australia. This appears to be due to the upwelling of older, regional groundwater closer the river. Other chemical parameters are consistent with this. This is a process that may be occurring in other similar river systems.
Satellite-driven downscaling of global reanalysis precipitation products for hydrological applications
Summary: The paper presents a methodology for using global precipitation products from satellite remote sensing to error-correct and downscale global atmospheric reanalysis precipitation data sets. It is shown that streamflow simulations from the satellite-adjusted precipitation reanalysis give similar statistics to the ones derived by high-resolution ground-based radar rainfall data sets. This approach can be applied globally to derive improved flood frequency maps over data-poor areas.
Modeling the snow surface temperature with a one-layer energy balance snowmelt model
Summary: This paper evaluates three improvements to an energy balance snowmelt model aimed to represent snow surface temperature while retaining the parsimony of a single layer. Surface heat flow is modeled using a forcing term related to the vertical temperature difference and a restore term related to the temporal gradient of surface temperature. Adjustments for melt water refreezing and thermal conductivity when the snow is shallow are introduced. The model performs well at the three test sites.
Accounting for environmental flow requirements in global water assessments
Summary: Freshwater ecosystems encompass the most threatened species on earth. Environmental flow requirements need to be addressed globally to provide sufficient water for humans and nature. We present a comparison of five environmental flow methods validated with locally calculated EFRs. We showed that methods based on monthly average flow such as the variable monthly flow method are more reliable than methods based on annual thresholds. A range of EFRs was calculated for large river basins.
Summary: Our virtual water network of the Roman World shows that virtual water trade and irrigation provided the Romans with resilience to interannual climate variability. Virtual water trade enabled the Romans to meet food demands from regions with a surplus. Irrigation provided stable water supplies for agriculture, particularly in large river catchments. However, virtual water trade also stimulated urbanization and population growth, which eroded Roman resilience to climate variability over time.
Building a field- and model-based climatology of local water and energy cycles in the cultivated Sahel – annual budgets and seasonality
Summary: Long-term average water and energy cycles are described for two main land cover types in the cultivated Sahel (millet crop and fallow bush). Mean seasonal cycles and annual budgets for all component variables were estimated from detailed field and model analysis. Evapotranspiration totals over 80% of rainfall for both covers, but with different time distribution and soil/plant contributions. The remainder is shared between runoff and deep drainage for the crop, but is only runoff for the fallow.
C. Velluet, J. Demarty, B. Cappelaere, I. Braud, H. B.-A. Issoufou, N. Boulain, D. Ramier, I. Mainassara, G. Charvet, M. Boucher, J.-P. Chazarin, M. Oï, H. Yahou, B. Maidaji, F. Arpin-Pont, N. Benarrosh, A. Mahamane, Y. Nazoumou, G. Favreau, and J. Seghieri Hydrol. Earth Syst. Sci., 18, 5001-5024, 2014 AbstractFinal Revised Paper (PDF, 704 KB)Discussion Paper (HESSD)
10 Dec 2014
Evaluation of root water uptake in the ISBA-A-gs land surface model using agricultural yield statistics over France
Summary: Regional French agricultural yield statistics are used to benchmark root water uptake representations in the ISBA-A-gs model. Key model parameters governing the inter-annual variability of the simulated biomass are retrieved. A complex multi-layer soil hydrology model does not outperform a simple bulk root-zone reservoir approach. This could be explained by missing processes/information in the model such as hydraulic redistribution and detailed soil properties.
Predicting East African spring droughts using Pacific and Indian Ocean sea surface temperature indices
Summary: Western Pacific SST gradients influence eastern East African precipitation in predictable ways. At seasonal and decadal timescales, warm equatorial western Pacific SSTs and cool eastern Pacific SSTs reduce precipitation in East Africa. The gradient between these regions can be used to make reasonably accurate forecasts in one of the world's most food-insecure regions. Recent warming in the western Pacific and stationary eastern Pacific conditions have produced large precipitation declines.