Topic
Surface runoff
About: Surface runoff is a research topic. Over the lifetime, 45130 publications have been published within this topic receiving 1106367 citations. The topic is also known as: streamflow & runoff.
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TL;DR: In this paper, the authors provided a global overview of groundwater depletion by assessing groundwater recharge with a global hydrological model and subtracting estimates of groundwater abstraction, and they estimated the total global groundwater depletion to have increased from 126 (±32) km3 a−1 in 1960 to 283 (±40) km 3 a −1 in 2000.
Abstract: [1] In regions with frequent water stress and large aquifer systems groundwater is often used as an additional water source. If groundwater abstraction exceeds the natural groundwater recharge for extensive areas and long times, overexploitation or persistent groundwater depletion occurs. Here we provide a global overview of groundwater depletion (here defined as abstraction in excess of recharge) by assessing groundwater recharge with a global hydrological model and subtracting estimates of groundwater abstraction. Restricting our analysis to sub-humid to arid areas we estimate the total global groundwater depletion to have increased from 126 (±32) km3 a−1 in 1960 to 283 (±40) km3 a−1 in 2000. The latter equals 39 (±10)% of the global yearly groundwater abstraction, 2 (±0.6)% of the global yearly groundwater recharge, 0.8 (±0.1)% of the global yearly continental runoff and 0.4 (±0.06)% of the global yearly evaporation, contributing a considerable amount of 0.8 (±0.1) mm a−1 to current sea-level rise.
1,367 citations
TL;DR: In this article, a system which determines slope, aspect, and curvature in both the downslope and across-slope directions is developed for an altitude matrix, and the upslope drainage area and maximum drainage distance are determined for every point within the altitude matrix.
Abstract: Land surface topography significantly affects the processes of runoff and erosion. A system which determines slope, aspect, and curvature in both the down-slope and across-slope directions is developed for an altitude matrix. Also, the upslope drainage area and maximum drainage distance are determined for every point within the altitude matrix. A FORTRAN 66 program performs the analysis.
1,316 citations
TL;DR: The physical nature of the erosion process was studied on carefully controlled field plats of Cecil clay located on several slopes, and losses from this strongly aggregated soil occurred primarily in the form of water stable aggregates.
Abstract: 1. The inherent weaknesses of the elutriation method of aggregate analysis are pointed out and the use of this method of aggregate analysis is questioned. 2. A mechanism is suggested to account for the slaking reaction of soils in the presence of excess water. 3. A direct method, with suitable apparatus for determining the water stable aggregate distribution in soils, is reported. 4. Several soils of the Cecil series with widely varying clay contents were found to have similar distribution of water stable aggregates. 5. Soils from different senses were found to be characterized by different distributions of water stable aggregates. 6. The physical nature of the erosion process was studied on carefully controlled field plats of Cecil clay located on several slopes. The losses from this strongly aggregated soil occurred primarily in the form of water stable aggregates. 7. Data are presented which show the effectiveness of winter legumes in controlling sheet erosion losses. The manner in which this type of "vegetative control" functions is reviewed. 8. Results on the use of various widths of strip crop for controlling sheet erosion are presented. The basic weakness of this type of "vegetative control" practice is pointed out.
1,300 citations
TL;DR: The Community Land Model (CLM) as discussed by the authors is the land component of the Community Climate System Model (CCSM) and has been extended with a carbon-nitrogen (CN) biogeochemical model that is prognostic with respect to vegetation, litter, and soil carbon and nitrogen states.
Abstract: [1] The Community Land Model is the land component of the Community Climate System Model. Here, we describe a broad set of model improvements and additions that have been provided through the CLM development community to create CLM4. The model is extended with a carbon-nitrogen (CN) biogeochemical model that is prognostic with respect to vegetation, litter, and soil carbon and nitrogen states and vegetation phenology. An urban canyon model is added and a transient land cover and land use change (LCLUC) capability, including wood harvest, is introduced, enabling study of historic and future LCLUC on energy, water, momentum, carbon, and nitrogen fluxes. The hydrology scheme is modified with a revised numerical solution of the Richards equation and a revised ground evaporation parameterization that accounts for litter and within-canopy stability. The new snow model incorporates the SNow and Ice Aerosol Radiation model (SNICAR) - which includes aerosol deposition, grain-size dependent snow aging, and vertically-resolved snowpack heating – as well as new snow cover and snow burial fraction parameterizations. The thermal and hydrologic properties of organic soil are accounted for and the ground column is extended to ∼50-m depth. Several other minor modifications to the land surface types dataset, grass and crop optical properties, surface layer thickness, roughness length and displacement height, and the disposition of snow-capped runoff are also incorporated. The new model exhibits higher snow cover, cooler soil temperatures in organic-rich soils, greater global river discharge, and lower albedos over forests and grasslands, all of which are improvements compared to CLM3.5. When CLM4 is run with CN, the mean biogeophysical simulation is degraded because the vegetation structure is prognostic rather than prescribed, though running in this mode also allows more complex terrestrial interactions with climate and climate change.
1,295 citations
TL;DR: In this article, the authors estimate that half of the closed forests of Brazilian Amazonia depend on deep root systems to maintain green canopies during the dry season, and as much as 15% of this deep-soil carbon turns over on annual or decadal timescales.
Abstract: DEFORESTATION and logging transform more forest in eastern and southern Amazonia than in any other region of the world1–3. This forest alteration affects regional hydrology4–11 and the global carbon cycle12–14, but current analyses of these effects neglect an important deep-soil link between the water and carbon cycles. Using rainfall data, satellite imagery and field studies, we estimate here that half of the closed forests of Brazilian Amazonia depend on deep root systems to maintain green canopies during the dry season. Evergreen forests in northeastern Para state maintain evapotranspiration during five-month dry periods by absorbing water from the soil to depths of more than 8m. In contrast, although the degraded pastures of this region also contain deep-rooted woody plants, most pasture plants substantially reduce their leaf canopy in response to seasonal drought, thus reducing dry-season evapotranspiration and increasing potential subsurface runoff relative to the forests they replace. Deep roots that extract water also provide carbon to the soil. The forest soil below 1 m depth contains more carbon than does above-ground biomass, and as much as 15% of this deep-soil carbon turns over on annual or decadal timescales. Thus, forest alteration that affects depth distributions of carbon inputs from roots may also affect net carbon storage in the soil.
1,288 citations