Showing papers on "Water cycle published in 1991"

Diurnal Variability of the Hydrologic Cycle in a General Circulation Model

Abstract: In the present Colorado State University GCM simulation-based analysis of the diurnal and semidiurnal variability of precipitation, precipitable water, evaporation, cloudiness, horizontal moisture flux convergence, and cloud radiative forcing, a realistic afternoon precipitation maximum is obtained over land in warm rainy regions, as well as an early morning maximum over the oceans. The model has been further used to investigate the bases for the oceanic diurnal-precipitation cycle; the results thus obtained indicate that such an oceanic cycle occurs even in the absence of neighboring continents, and tends to have a morning maximum, although the observed phenomenon is generally stronger than the results indicate.

Snow hydrology of a headwater Arctic basin: 1. Physical measurements and process studies

Abstract: The hydrologic cycle of an Arctic watershed is dominated by such physical elements as snow, ice, permafrost, seasonally frozen soils, wide fluctuations in surface energy balance, and phase change of snow and ice to water. Hydrologic data collected over a 5-year period (1985-1989) from an Arctic watershed in northern Alaska are presented. Processes related to snow accumulation, redistribution, ablation, evaporation and subsequent snowmelt-generated runoff are discussed. The total water content of the snowpack at the end of winter had comprised between 28 and 40% of the annual precipitation. Redistribution of snow on the ground by the wind is a major factor in increasing the snowmelt runoff. Much of the redistributed snow accumulates in the valley bottom along the stream and also along depressions on the hillslopes. These depressions are small surface drainage channels that are referred to as water tracks. Partitioning of the snowmelt into runoff, evaporation and increased soil water storage in the active layer was carried out on the plot and watershed scale. Over a 5-year period, the volume of snowmelt runoff varied from 50 to 66% of the average watershed snowpack, while evaporation varied from 20 to 34% and soil moisture storage increased between 10 and 19%.more » Much greater variation in these hydrologic components occurred at the plot scale.« less

An Interdisciplinary Field Study of the Energy and Water Fluxes in the Atmosphere–Biosphere System over Semiarid Rangelands: Description and Some Preliminary Results

Abstract: Arid and semiarid rangelands comprise a significant portion of the earth's land surface. Yet little is known about the effects of temporal and spatial changes in surface soil moisture on the hydrologic cycle, energy balance, and the feedbacks to the atmosphere via thermal forcing over such environments. Understanding this interrelationship is crucial for evaluating the role of the hydrologic cycle in surface-atmosphere interactions. This study focuses on the utility of remote sensing to provide measurements of surface soil moisture, surface albedo, vegetation biomass, and temperature at different spatial and temporal scales. Remote-sensing measurements may provide the only practical means of estimating some of the more important factors controlling land surface processes over large areas. Consequently, the use of remotely sensed information in biophysical and geophysical models greatly enhances their ability to compute fluxes at catchment and regional scales on a routine basis. However, model cal...

Modeling basin-scale hydrology in support of physical climate and global biogeochemical studies: An example using the Zambezi River

Abstract: Human activity is an important agent defining the contemporary hydrologic cycle. We have documented the potential impacts of impoundment, land use change and climate change on the Zambezi River system in southern Africa and found that they can be substantial. A full analysis requires construction and parameterization of a simulation for the entire catchment. This paper develops a strategy for implementing catchment-scale models of the major hydrologic processes operating within the basin. A coherent data set for calibrating the models has also been assembled. The algorithms consist of a Water Balance (WBM) and a Water Transport (WTM) operating at 1/2° spatial scale and at monthly timesteps. These models transform complex patterns of regional climatology into estimates of soil water, evapotranspiration, runoff, and discharge through rivers of various size. The models are dependent on the characteristics of the terrestrial surface, principally soil texture and land cover. A simulated river network is also required. Additional tabular data sets are essential for model testing and calibration. These include subcatchment areas; observed river discharge at selected points; flooding, storage and loss characteristics of major wetlands; floodwave translation; and, volume, surface area, withdrawal and evaporative losses from impoundments. An important design consideration for the numerous impoundments in the Zambezi requires an understanding of the seasonal variation in discharge, in particular how it might respond to climate and land use change. The research strategy offered here lays a framework for addressing such issues. Although the primary focus of this work is hydrologic, we discuss how the model can be extended to consider constituent transport and biogeochemical cycling issues at the continental scale.

Probable impact of deforestation on hydrological processes

Abstract: The various ways in which the forest cover may influence the atmospheric and soil processes controlling the hydrological cycle are examined. Case studies of extensive deforestation affecting the rainfall pattern are reviewed.

The role of water vapor in climate. A strategic research plan for the proposed GEWEX water vapor project (GVaP)

Abstract: The proposed GEWEX Water Vapor Project (GVaP) addresses fundamental deficiencies in the present understanding of moist atmospheric processes and the role of water vapor in the global hydrologic cycle and climate. Inadequate knowledge of the distribution of atmospheric water vapor and its transport is a major impediment to progress in achieving a fuller understanding of various hydrologic processes and a capability for reliable assessment of potential climatic change on global and regional scales. GVap will promote significant improvements in knowledge of atmospheric water vapor and moist processes as well as in present capabilities to model these processes on global and regional scales. GVaP complements a number of ongoing and planned programs focused on various aspects of the hydrologic cycle. The goal of GVaP is to improve understanding of the role of water vapor in meteorological, hydrological, and climatological processes through improved knowledge of water vapor and its variability on all scales. A detailed description of the GVaP is presented.

Climate Variability and Climate Change

Abstract: Changes of variability with climate change are likely to have a substantial impact on vegetation and society, rivaling the importance of changes in the mean values themselves. A variety of paleoclimate and future climate simulations performed with the GISS global climate model is used to assess how the variabilities of temperature and precipitation are altered as climate warms or cools. In general, as climate warms, temperature variability decreases due to reductions in the latitudinal temperature gradient and precipitation variability increases together with the intensity of the hydrologic cycle. If future climate projections are accurate, the reduction in temperature variability will be minimized by the rapid change in mean temperatures, but the hydrologic variability will be amplified by increased evapotranspiration. Greater hydrologic variability would appear to pose a potentially severe problem for the next century.

Clouds, the earth's radiation budget, and the hydrologic cycle

Abstract: Water vapor plays a key role in climate change scenarios through the water vapor feedback loop. The distribution of water vapor obviously controls the distribution of clouds, but the opposite is also true because clouds carry out important vertical redistributions of the vapor. This paper presents comparisons of water vapor observations with general circulation model simulations of the distribution of water vapor and its effects on the Earth's radiation budget. The ability of the model to simulate the seasonally changing cloud radiative forcing is also discussed. Finally, the need for long-term monitoring of these fields is emphasized.

Sensitivity of Water Balance to Climate Change and Variability

Abstract: The IIASA Water Resources Project addresses the development and application of methods and procedures needed to identify policy strategies for water resources planning and operation. Due to population growth, industrial and agricultural development, increased pollution and the impact of global climatic change, the reliability of water supply may substantially decrease in various parts of the world, causing serious social and economic problems. There is a need for studies on possible policy actions, aimed at the development of more resilient and more robust water systems, based on a sound understanding of geophysical processes which regulate the hydrological cycle in a changing environment. This paper concerns methodological tools for the sensitivity analysis of the water balance components to changing climatic forcings. It presents a new meso-scale hydrological model based on the stochastic storage theory, and its application to the sensitivity analysis and to water balance impact studies. The model allows to calculate runoff characteristics, evaporation and catchment storage on the basis of standard climatological data, and eventually on the basis of alternative climate scenarios. It was tested for a number of river catchments in Europe and Africa. The possible effects of the expected changes in air temperature and precipitation will give rise to various problems in many fields of water resource management. For this reason, the paper may be of interest not only to hydrologists, but also to decision makers in water industry.

Modelling of the snow-water equivalent in the mountain environment

Abstract: The water equivalent (SWE) of the seasonal snow cover can be an important component of the water cycle in mountainous areas, and the knowledge of this temporary storage term may for example be very valuable for predicting seasonal discharge, for making short-range discharge forecasts and also for assessing water quality aspects Direct measurements of the SWE usually refer to index points and are seldom part of the standard meteorological networks Therefore it may be advantageous to simulate this storage term based on the available meteorological data The choice of the appropriate type of model will largely depend on the purpose of the simulation and the data availability For operational forecasting and prediction practices, various conceptual models describing snow accumulation, melt and internal processes as well as runoff processes in a rather general way are usually sufficient if a minimal data requirement is met To answer more complex questions such as the hydrological consequences of climatic or land-use changes, conceptual models may serve as an initial step in a "scale analysis" of the most important variables such as precipitation and air temperature or of basin-specific parameters such as forest cover However, any modelled scenario will always be an artifact of the particular model used, and caution is required when interpreting the results With the introduction of new measurement systems for meteorological variables with a high temporal resolution new possibilities arise for the application of physically-ba sed approaches in modelling SWE and for the understanding of individual processes in the immediate surroundings of such a station However, unresolved problems are encountered when trying to apply detailed simulation models on a catchment scale Possible key areas of further research are improved interpolation techniques for meteorological data, taking into account local and mesoscale climatic conditions, the coupling of meteorological and hydrological models, and the application of remote sensing techniques to validate intermediary results of these spatially distributed models such as snow covered area or, preferably, SWE

An energy balance climate model with hydrological cycle: 1. Model description and sensitivity to internal parameters

Abstract: A thermodynamical model designed to illustrate the effect of a hydrological cycle on climate sensitivity is presented. The model contains three climatic variables: two temperatures referring to an idealized atmosphere and ocean, respectively, and atmospheric humidity. The independent variables are time and latitude. Atmosphere and ocean are coupled by radiation and convection at their interface. Some structure of the atmospheric circulation is retained by differentiating between the dynamics of a low latitude zone (0° - ϕH) and that of a high latitude zone (ϕH-90°), where ϕH ≈ 30° is the intersection of meridional temperature gradient and critical gradient for baroclinic instability. The atmospheric transport is split into an advective and a diffusive part, while the oceanic transport is approximated by pure diffusion. The coefficients associated with horizontal and vertical motion are modelled in terms of temperature gradients. The predicted water vapor gives rise to precipitation and clouds and influences (via cloud cover and greenhouse effect) the radiation balance of the system. The model is integrated for annual mean conditions until an asymptotic equilibrium is reached. The free (internal) parameters of the system are determined by optimization methods so that simulated temperature, heat flux and hydrological cycle are in close agreement with observations. The sensitivity of the model is governed by radiation parameters. Of these, the cloud albedo is the most sensitive quantity. By contrast, the model is relatively little affected by parameters associated with horizontal and vertical transport of heat.

Climate and the equilibrium state of land surface hydrology parameterizations

Abstract: For given climatic rates of precipitation and potential evaporation, the land surface hydrology parameterizations of atmospheric general circulation models will maintain soil-water storage conditions that balance the moisture input and output. The surface relative soil saturation for such climatic conditions serves as a measure of the land surface parameterization state under a given forcing. The equilibrium value of this variable for alternate parameterizations of land surface hydrology are determined as a function of climate and the sensitivity of the surface to shifts and changes in climatic forcing are estimated.

An energy balance climate model with hydrological cycle: 2. Stability and sensitivity to external forcing

Abstract: The stability of a thermodynamic climate model with three prognostic variables (two for temperature and one for humidity) is investigated. Two stable equilibrium points are found which, in agreement with earlier work, refer to the current (warm) climate and a cold climate. However, perturbations in global temperature must be extremely large (< −20°C) to drive the warm climate into the cold climate. The domains of attraction in phase space are dependent on temperature, but also on humidity. Starting from an ice covered state, the climatic trajectory approaches the present state, if humidity is above some threshold value initially, but evolves into the cold state, if it lies below. Numerical experiments show that the model is not only remarkably stable to internal perturbation but also relatively insensitive to changes in external parameters. The solar constant must be reduced by approximately 20% to obtain total ice cover; the atmospheric CO2- content must be doubled to obtain 1.5°C global warming. However, the surface temperature response of the model increases to 3.5°C if cloud temperature rather than cloud height is held fixed. In addition to the cloud height feedback, other positive feedbacks are ice albedo, water vapor and the oceanic heat flux. The great stabilizers of the model are IR damping and the atmospheric heat transport which is assumed to depend quadratically on the meridional temperature gradient. In addition, precipitation and evaporation effectively damp the surface temperature response of the all ocean model to increased atmospheric trace gases.

Condensed Paper Clouds, the Earth's radiation budget, and the hydrologic cycle

Abstract: Randall, D.A. and Tjemkes, S., 1991. Clouds, the Earth's radiation budget, and the hydrologic cycle. Palaeogeogr., Palaeoclimatol., Palaeoecol. (Global Planet. Change Sect.), 90:3 9. Water vapor plays a key role in climate change scenarios through the water vapor feedback loop. The distribution of water vapor obviously controls the distribution of clouds, but the opposite is also true because clouds carry out important vertical redistributions of the vapor. This paper presents comparisons of water vapor observations with general circulation model simulations of the distribution of water vapor and its effects on the Earth's radiation budget. The ability of the model to simulate the seasonally changing cloud radiative forcing is also discussed. Finally, the need for long-term monitoring of these fields is emphasized.

Ocean Margin Processes in Global Change: Report of the Dahlem Workshop on Ocean Margin Processes in Global Change, Berlin, 1990, March 18-23

Abstract: Dissolved and Particulate Organic Matter in Rivers N, P, and Si Retention along the Aquatic Continuum from Land to Ocean Present and Future Roles of Ocean Margins in Regulating Marine Biogeochemical Cycles of Trace Elements Flux and Fate of Fluvial Sediment and Water in Coastal Seas Chemical Exchange at the Air-Coastal Sea Interface What Regulates Boundary Fluxes? Biologically Mediated Removal, Transformation, and Regeneration of Dissolved Elements and Compounds Circulation Processes in Relation to Material Fluxes Heterogeneous Reactions Accumulation and Regeneration: Processes at the Benthic Boundary Layer Dissolved Organic Carbon Enigma: Implications for Ocean Margins Fractal Theory and Time Dependency in Ocean Margin Processes Coastal Eutrophication: Causes and Consequences Environmental Capacity of the Ocean Margins: The Impact of Human Alterations of the Hydrological Cycle Morphological and Ecological Effects of Sea Level Rise: An Evaluation for the Western Wadden Sea Response of Ocean Margin Systems to Natural and Anthropogenic Perturbations The Coastal Organic Carbon Cycle: Fluxes, Sources, and Sinks Climatic and Environmental Implications of Biogas Exchange at the Sea Surface: Modeling and the Marine Biologic Sulfur Cycle Geophysiology of the Oceans.

Atmospheric water vapor transport: Estimation of continental precipitation recycling and parameterization of a simple climate model

Abstract: The advective transport of atmospheric water vapor and its role in global hydrology and the water balance of continental regions are discussed and explored. The data set consists of ten years of global wind and humidity observations interpolated onto a regular grid by objective analysis. Atmospheric water vapor fluxes across the boundaries of selected continental regions are displayed graphically. The water vapor flux data are used to investigate the sources of continental precipitation. The total amount of water that precipitates on large continental regions is supplied by two mechanisms: (1) advection from surrounding areas external to the region; and (2) evaporation and transpiration from the land surface recycling of precipitation over the continental area. The degree to which regional precipitation is supplied by recycled moisture is a potentially significant climate feedback mechanism and land surface-atmosphere interaction, which may contribute to the persistence and intensification of droughts. A simplified model of the atmospheric moisture over continents and simultaneous estimates of regional precipitation are employed to estimate, for several large continental regions, the fraction of precipitation that is locally derived. In a separate, but related, study estimates of ocean to land water vapor transport are used to parameterize an existing simple climate model, containing both land and ocean surfaces, that is intended to mimic the dynamics of continental climates.

Evaluating the water resource impacts of climatic warming in cold alpine regions by the water balance model: modeling the urumqi river basin

Abstract: In view of the tendency of global climatic warming, the water balance model is employed to estimate the runoff changes in the Urumqi River Basin, Xinjiang Region, China, under ten climate change scenarios, which are combinations of temperature increases by 2K and 4K with precipitation change of 0, ±10% and ±20%, respectively, as the atmospheric concentration of carbon dioxide increases. The results suggest that runoff changes mainly depend on the precipitation change in the glacier-free or less glacierized basins in cold alpine regions. Effect of temperature on runoff becomes marked gradually with the increase in precipitation. Runoff from glacierized areas, however, is much more sensitive to the temperature change.

OMEGA: Impact of Spatial Variability of Infiltration Parameters on Catchment Response

Abstract: OMEGA is a rainfall-runoff model for event or continuous simulation that incorporates to a large extent the physical conceptualization of the hydrological processes. This is principally achieved in the description of the highly nonlinear processes of infiltration, ponding, and redistribution of water in soil that play key roles as interfaces of surface and groundwater components of the hydrologic cycle. OMEGA is a distributed model with respect to the parameters and the inputs. Spatial variability is taken into consideration, and phenomena such as the movement of a storm over the watershed can be considered.

Applications of the EOS SAR to monitoring global change

Abstract: The SAR employed by NASA's Earth Observing System (EOS) is a multifrequency multipolarization radar which can conduct global monitoring of geophysical and biophysical parameters. The present discussion of the EOS SAR's role in global monitoring emphasizes geophysical product variables applicable to global hydrologic, biogeochemical, and energy cycle models. EOS SAR products encompass biomass, wetland areas, and phenologic and environmental states, in the field of ecosystem dynamics; soil moisture, snow moisture and extent, and glacier and ice sheet extent and velocity, in hydrologic cycle studies; surface-wave fields and sea ice properties, in ocean/atmosphere circulation; and the topography, erosion, and land forms of the solid earth.

Atmospheric water vapor flux convergence and basin water balance

Abstract: Atmospheric vapor flux convergence is introduced for the estimation of the water balance in a river basin. Flux convergence is calculated using the ECMWF global analysis data, and compared with the observed data in Chao Phraya river basin, Thailand. Through the balance equation of hydrological cycle, discharge is estimated from vapor flux convergence and is compared with observations. It was found that the absolute value of flux convergence is not applicable, but inclusion of a factor provided better estimation for the case under study. Such information is expected to give basin scale evaporation or water storage in a basin.

Water Saving and High Yielding Irrigation Model on Lowland Paddy Field

Abstract: A 5-year (1984-1988) research aimed at the optimum drainage-irrigation model that makes the best utilization of rainfall to effectuate a high yield with a least amount of water consumption in irrigation and discharge in drainage, has been carried out on plots at experimental station of CNRRI, Hangzhou. Among the treatments of the test, various water depth over the paddy under irrigation and depth to water within the soil under drainage are specified for the various growth period of the rice plant. The water budget of the irrigation and drainage as an integral is obtained from the unified management of the rainfall, irrigation water applied, soil water and ground water that takes part in the hydraulic cycle.

Evolution of the Martian hydrosphere

Abstract: The concept of the hydrological cycle is one of the greatest achievements in the understanding of nature. Leonardo da Vinci seems to have held two concurrent views of the cycle: an external process in which evaporation from ponded areas leads to precipitation and runoff from the land; and an internal process in which subsurface pressures from within the Earth force water upward. Endogenetic hypotheses for valley genesis on Mars maintain the necessary prolonged ground water flows by hydrothermal circulation associated with impact cratering or with volcanism. Ocean formation on Mars was episodic, mostly evidenced by the latest episodes. Coincident cataclysmic flood discharges to the northern plains, probably triggered by Tharsis volcanism, would lead to immense consequences. Potential volumes of ponded water are summarized. The outflow channels have a complex history of flooding events over a prolonged period of planetary history. It is hypothesized that episodic outbursts of concurrent discharge was triggered by planetary scale volcanism. The consequences of such episodes are summarized.