Streamflow

About: Streamflow is a research topic. Over the lifetime, 14338 publications have been published within this topic receiving 433445 citations.

Ecological effects of perturbation by drought in flowing waters

Abstract: 1. Knowledge of the ecology of droughts in flowing waters is scattered and fragmentary, with much of the available information being gathered opportunistically. Studies on intermittent and arid-zone streams have provided most of the information. 2. Drought in streams may be viewed as a disturbance in which water inflow, river flow and water availability fall to extremely low levels for extended periods of time. As an ecological perturbation, there is the disturbance of drought and the responses of the biota to the drought. 3. Droughts can either be periodic, seasonal or supra-seasonal events. The types of disturbance for seasonal droughts are presses and for supra-seasonal droughts, ramps. 4. In droughts, hydrological connectivity is disrupted. Such disruption range from flow reduction to complete loss of surface water and connectivity. The longitudinal patterns along streams as to where flow ceases and drying up occurs differs between streams. Three patterns are outlined: 'downstream drying', 'headwater drying' and 'mid-reach drying'. 5. There are both direct and indirect effects of drought on stream ecosystems. Marked direct effects include loss of water, loss of habitat for aquatic organisms and loss of stream connectivity. Indirect effects include the deterioration of water quality, alteration of food resources, and changes in the strength and structure of interspecific interactions. 6. Droughts have marked effects on the densities and size- or age-structure of populations, on community composition and diversity, and on ecosystem processes. 7. Organisms can resist the effects of drought by the use of refugia. Survival in refugia may strongly influence the capacity of the biota to recover from droughts once they break. 8. Recovery by biota varies markedly between seasonal and supra-seasonal droughts. Faunal recovery from seasonal droughts follows predictable sequences, whilst recovery from supra-seasonal droughts varies from one case to another and may be marked by dense populations of transient species and the depletion of biota that normally occur in the streams. 9. The restoration of streams must include the provision of drought refugia and the inclusion of drought in the long-term flow regime.

The geomorphologic structure of hydrologic response

Abstract: A unifying synthesis of the hydrologic response of a catchment to surface runoff is attempted by linking the instantaneous unit hydrograph (IUH) with the geomorphologic parameters of a basin. Equations of general character are derived which express the IUH as a function of Horton's numbers RA, RB, and RL; an internal scale parameter LΩ and a mean velocity of streamflow v. The IUH is time varying in character both throughout the storm and for different storms. This variability is accounted for by the variability in the mean streamflow velocity. The underlying unity in the nature of the geomorphologic structure is thus carried over to the great variety of hydrologic responses that occur in nature. An approach is initiated to the problem of hydrologic similarity.

Estimates of Freshwater Discharge from Continents: Latitudinal and Seasonal Variations

Abstract: Annual and monthly mean values of continental freshwater discharge into the oceans are estimated at 18 resolution using several methods. The most accurate estimate is based on streamflow data from the world’s largest 921 rivers, supplemented with estimates of discharge from unmonitored areas based on the ratios of runoff and drainage area between the unmonitored and monitored regions. Simulations using a river transport model (RTM) forced by a runoff field were used to derive the river mouth outflow from the farthest downstream gauge records. Separate estimates are also made using RTM simulations forced by three different runoff fields: 1) based on observed streamflow and a water balance model, and from estimates of precipitation P minus evaporation E computed as residuals from the atmospheric moisture budget using atmospheric reanalyses from 2) the National Centers for Environmental Prediction‐National Center for Atmospheric Research (NCEP‐NCAR) and 3) the European Centre for Medium-Range Weather Forecasts (ECMWF). Compared with previous estimates, improvements are made in extending observed discharge downstream to the river mouth, in accounting for the unmonitored streamflow, in discharging runoff at correct locations, and in providing an annual cycle of continental discharge. The use of river mouth outflow increases the global continental discharge by ;19% compared with unadjusted streamflow from the farthest downstream stations. The river-based estimate of global continental discharge presented here is 37 288 6 662 km3 yr21, which is ;7.6% of global P or 35% of terrestrial P. While this number is comparable to earlier estimates, its partitioning into individual oceans and its latitudinal distribution differ from earlier studies. The peak discharges into the Arctic, the Pacific, and global oceans occur in June, versus May for the Atlantic and August for the Indian Oceans. Snow accumulation and melt are shown to have large effects on the annual cycle of discharge into all ocean basins except for the Indian Ocean and the Mediterranean and Black Seas. The discharge and its latitudinal distribution implied by the observation-based runoff and the ECMWF reanalysis-based P‐E agree well with the river-based estimates, whereas the discharge implied by the NCEP‐NCAR reanalysis-based P‐E has a negative bias.