Generation Of Surface Runoff Infiltration Excess Surface Runoff Generation

The classical model of surface runoff generation is by an infiltration excess mechanism in which rainfall intensity exceeds the local infiltration capacity of the soil for a sufficient period of time for any depression storage at the soil surface to be satisfied such that downslope flow is initiated. This will not occur where the permeability of the soil is high in comparison with expected rainfall intensities, and even when this is not the case there may be an initial period when all the...

Biogenic Nonmethane Hydrocarbons

Nonmethane volatile organic compounds (NMVOCs) are emitted from a wide variety of both anthropogenic and biogenic sources. Major anthropogenic sources of NMVOCs include combustion of fossil fuels, solvent evaporation and biomass burning, while direct emissions from plants are the largest biogenic source. Over 90 of the total NMVOCs entering the atmosphere are biogenic (Guenther et al., 1995 Miiller, 1992). Recent estimates of the upper limit of global NMVOC emissions from biogenic sources range...

Hydraulic Construction Hypothesis

Some observers have argued that the recent fall and rise in sea level were the result of human activities. They suggest that the widespread development of hydraulic structures (e.g., dams, reservoirs, irrigation systems) in the Volga River basin, beginning in the 1950s, led to a sharp decline in Volga flow. The filling of many reservoirs built along the rivers flowing into the Caspian, the increase in industrial and muni cipal water use by several times, and changes in the water regime of the...

Government Flood Mitigation Policies Failed

Past structural and nonstructural approaches to flood mitigation have not worked, and major past efforts to improve U.S. flood policies have not succeeded. Only 10 of those flood damaged had flood insurance. The floods re-enforced the need to make improvements in floodplain use policies and the federal insurance programs. The considerable failure of the levee systems in 1993 and 1997 revealed that not all levees, particularly agricultural protection levees, can be built in a cost-effective...

Evaluating The Spatial Distribution Of Evaporation

SUSAN MORAN, AND JOHN M. NORMAN Evaporation of water from soil and plant surfaces forms the connecting link between the energy balance and the water balance at Earth's surface. This phenomenon influences the large-scale circulation of the planetary atmosphere, affects soil moisture content that in turn affects hydrologie response, and regulates the microscale carbon dioxide uptake of stomata in individual plant leaves. The vast range of scales encompassed by the process of...

References

Morocco Country development strategy statement (FYs 1987-1991). Annex C The agricultural sector in Morocco A description, unpublished report, United States Agency for International Development, Washington, DC, February 1986. Bencherifa, A., Agropastoral systems in Morocco. Cultural ecology of tradition and change, Ph.D thesis, Clark University, Worcester, MA, 1986. Bencherifa, A., Agropastorale Organisations formen im Atlantischen Marokko, Die Erde, 119, 1-13, 1988a. Bencherifa, A., Le...

Dynamic Routing Model

When the complete Saint-Venant equations (1) and (2) are used, the routing model is known as a dynamic routing model. With the advent of high-speed computers, Stoker (1953) and Isaacson et al. (1954, 1956) first attempted to use the complete Saint-Venant equations for routing Ohio River floods. Since then, much effort has been expended on the development of dynamic routing models. Many models have been reported in the literature (Fread, 1985, 1992 Liggett and Cunge, 1975). Dynamic routing...

Geographic And Seasonal Distribution Origin

Typically, in the Atlantic Ocean basin tropical storms and hurricanes develop over warm water between around 10 N to 35 N, generally, during the summer and fall. During an average year about 16 tropical cyclones develop in the eastern Pacific and approximately 10 in the Atlantic including the Gulf of Mexico and Caribbean Sea (Neumann, 1993). During the period of record, tropical cyclones fail to develop south of the equator in the Western Hemisphere east of 130 W because of one or more of the...

Overview Atmospheric Chemistry

The study of atmospheric chemistry focuses on how chemical constituents cycle through the atmosphere. Excluding water vapor (which can account for as much as 2 to 3 of the volume of the atmosphere under extremely moist conditions), more than 99.9 of the remaining dry atmosphere is comprised of nitrogen (78.1 ), oxygen, (20.9 ), and argon (0.93 ). Unlike the study of conventional meteorology, where the atmosphere is generally treated as a bulk medium, atmospheric chemistry focuses on each...

Ai

Where (j) represents any dependent variable or functional quantity (Q, sc, sm, A, A0, q, h). Spatial derivatives are approximated at point (x', t') by a forward-difference quotient located between two adjacent time lines according to weighting factors of 9 (the ratio At' At shown in Fig. 1) and 1 - 6, i.e., Nonderivative terms are approximated with weighting factors at the same time level point (x', ) where the spatial derivatives are evaluated, i.e., The weighted four-point implicit scheme is...

Stratospheretroposphere Exchange

The exchange of mass between the stratosphere and troposphere is important to the chemistry of both regions as it brings chemical species with sources in the troposphere (such as CFCs) into the stratosphere, while species with stratospheric origin (such as ozone) can be brought into the troposphere. Thus, the transport can be important for driving the chemistry in both regions. Analogous to the boundary layer being isolated from the free troposphere because of the presence of a substantial...

Short Term Forecasting of Streamflows

A number of investigators have evaluated the benefits of streamflow forecast using the Kalman filter. For example, Georgakakos (1986) studied the performance of a hydrometeorological model for streamflow forecasting using 6-h data for Bird Creek, a 2344 km2 catchment in Oklahoma. A precipitation forecasting model was developed and coupled to a modified version of the U.S. National Weather Service rainfall-runoff model to produce the streamflow forecast. Variables such as soil moisture storages...

Aerosols from Biomass Burning

The burning of living and dead vegetation (biomass burning) is widespread over Earth, and this is a globally significant source for aerosols and for a variety of radiatively active and chemically reactive trace gases. Most of the biomass burned is caused by human activities as opposed to natural fires, and this mainly occurs in the tropics, involving savannas more than forests (Hao and Liu, 1994). Some burning sources are persistent, but emissions from savanna burning vary biennially because...

Principles Of Soil Water Movement

Through experiments on saturated water flow through sand beds, Darcy18 found that the rate of flow, Q (L3 T), through a cross-sectional area A (L2), is directly propor- Figure 7 Changes in water retention characteristics between sorption and desorption.16 Figure 7 Changes in water retention characteristics between sorption and desorption.16

Biomass Burning

Biomass fires are both natural and anthropogenic in origin. The natural trigger is lightning, which leads to mid- and high-latitude fires and episodes of smoke and pollution associated with them. Lightning is also prominent in tropical regions when the dry season gives way to the wet season and lightning in convective systems ignites dry vegetation. Atmospheric consequences of biomass fires are complex. When considering the impacts of fires for a given ecosystem, inputs of fires must be...

Sources Producing Primary And Secondary Particles Primary Particles from Oceans Sea Salt Aerosol

Surface winds cause the production of aerosols from the sea as well as from the land. The effects of the wind over the ocean are mediated by breaking waves, bursting bubbles, and to a lesser extent the formation of large spume droplets torn from waves by strong winds. The seasalt injected into the atmosphere is another of the large sources for aerosols on a mass basis, of the order of 1000 to 10,000 Tg yr (Blanchard, 1983). One reason for the large uncertainty in this estimate is that there is...

Stratospheric Chemistry Understanding The Ozone Layer

Ozone was discovered in 1839 by the German scientist Christian Frederich Schonbein at the University of Basel in Switzerland. Because of its pungent odor, its name was taken from the Greek word ozein, meaning odor. Schonbein's research, subsequent to his discovery, focused on verifying his hypothesis that ozone was a natural trace constituent of the atmosphere. As a result of interest in the late nineteenth century, there are a surprisingly large number of ambient measurements during that time....

Displaced Populations in Sudan

Sudan has a large population of displaced people who have left their original villages and moved elsewhere, often to urban settlements. The Commission of Displaced (COD) estimates that 3.5 million people had been displaced by 1991, of which 0.6 to 1.5 million were in the greater Khartoum area (Kuch, 1993). The major factors forcing the migrations were civil war in the south, which erupted during the dry summer of 1983, and the 1984 drought that resulted in the worst famine to hit northern Sudan...

Hurricanes In North American History

The word hurricane derives from the Spanish hurac n, itself derived from the dialects of indigenous peoples of the Caribbean and Latin America (Dunn and Miller, 1964). 'Hunraken' was the name of the Mayan storm god, and 'Huraken' was the god of thunder and lightning for the Quiche of southern Guatemala (Henry et al., 1994). The Tainos and Caribe tribes of the Caribbean called their God of Evil by the name Huracan. Other indigenous dialects included words such as aracan, urican, and hurivanvucan...

Particle Size Distribution

Size is the most important single characteristic of an aerosol particle. For a spherical particle, diameter (or radius) is the usual reported dimension. When a particle is not spherical, the size can be reported either in terms of a length scale characteristic of its silhouette or of a hypothetical sphere with equivalent dynamic properties, such as settling velocity in air. For example, the aerodynamic diameter of a particle represents the diameter of a unit density (pp 1 g cm3) sphere having...

Discovery Of Effect Of El Ninosouthern Oscillation On Australia

India suffered a severe drought and famine during 1877. Sir Henry Blanford, the director of the Indian Meteorological Service, noted the very high atmospheric pressures over Asia at the time and requested pressure information from other meteorologists around the world. Sir Charles Todd, the South Australian government observer noted that pressures were also high during 1877 over Australia, and much of the country suffered from drought that year. Todd compared earlier droughts and concluded that...

Perceptibility Parameters for Quantification of Uniform Haze Impairment

Whereas work discussed in the previous sections has emphasized detection thresholds of layered hazes, specifically plumes, other researchers have concentrated their efforts in establishing the change in image appearance required to just notice a difference in image sharpness. Early work focused on establishing the just noticeable difference between a scene where an object viewed against the same background could just be seen and one where that object could not be identified. This threshold work...

Stochastic Streamflow Forecasting

Over the past two decades, considerable research has been carried out in hydrology for developing stochastic models for short- and long-term forecasting of river flows. The form of these models generally follows the ARMA, ARMAX, and transfer function type of models (Box and Jenkins, 1976), with the last two proving to be more reliable for multiple forecasting periods (Burns and McBean, 1985 Awwad and Valdes, 1992). After defining the mathematical model, usually in a state-space form, the Kalman...

Deposition Velocity Estimates

The great diversity of airborne trace chemical properties, surface conditions, and environmental conditions prevents the generation of universally applicable dry deposition parameterization schemes. Studies have tended to focus on substances important in atmospheric chemistry or likely to be harmful to human health, biota, and man-made materials. The types of surface most often chosen for investigation are ones that are fairly common in a given region, because the total amount of substances...

Formulation Of Deposition Velocity

A common simple method of evaluating Eq. (1) is by analogy to Ohm's Law, where F corresponds to current, Vd corresponds to the inverse of the total resistance, and C corresponds to the voltage, referenced to electrical ground corresponding to a concentration of zero that is assumed to occur somewhere in the surface. From this analogy, the deposition velocity can be expressed in terms of three resistances in series. Here, Ra represents the aerodynamic resistance to transfer associated with...

Rainfall Variability

Rainfall in southern Africa varies temporally with annual, seasonal, and daily variations in the amount of rainfall received. Southern Africa, for example, experiences a high level of intraannual and intcrannual rainfall variability (Tyson, 1986). Rainfall occurs in the summer months across the central and northeastern parts of the country * Precipitation usually includes the deposition of water in solid or liquid form including tain, dew, snow, hail (Goudie, 1994). In this chapter rainfall...

Recharge and Downslope Flow in a Saturated Zone

In fully saturated soil the propagation of the effects of changes in the boundary conditions, such as those due to recharge, is much more rapid than in the unsaturated zone. In shallow subsurface systems, such as where a shallow soil overlays an impermeable rock bed, most of the downslope flow toward stream channels will take place in the saturated zone. Because of the more rapid dissipation of local pressure differences in the saturated zone, a description of flow processes based on Darcy's...

Kenneth E Pickering

In the early 1980s it was recognized that observed free tropospheric mixing ratios of some trace gases could not be explained simply by large-scale transport and eddy diffusion. Crutzen and Gidel (1983), Gidel (1983), and Chatfield and Crutzen (1984) hypothesized that convective clouds played an important role in rapid atmospheric vertical transport of trace species and tested parameterizations of convective transport in atmospheric chemical models. At nearly the same time evidence was shown of...

Long Term Forecasting of Streamflows

Forecasting Models Using Climatic Precursors. Long-term forecasting of hydrologic variables requires climate forecasts. As mentioned in the section on long-term precipitation forecasting, the increase in predictive skills of the models to forecast climatic anomalies based on the ENSO phenomena have provided renewed impetus for hydrologic forecasting. There have been a significant number of contributions to hydrologic forecasting using climatic precursors. For example, the hydrologic forecasting...

Definition Of Floods

Streams are linear water features that flow under the impetus of gravity. The amqunt of water contained in a stream is usually regulated by contributions of groundwater and surface runoff to the stream channel (Zaslavsky and Sinai, 1981 Knighton, 1998). Much of the time water in a stream flows within the confines of its channel. When inputs of water increase sufficiently, stream discharge leaves the stream channel and covers all or parts of the adjacent floodplain. Since the floodplain surface...

Global Distribution Of Tropospheric Ozone

The distribution of tropospheric ozone can be determined from the analyses of satellite data sets obtained independently from two different instruments The Total Ozone Mapping Spectrometer (TOMS) and the Stratospheric Aerosol and Gas Experiment (SAGE). Between October 1978 and May 1993, TOMS functioned on the Nimbus 7 satellite and provided daily maps of the distribution of total ozone. Additional TOMS were launched in 1991 (on the Russian Meteor satellite) and two in 1996 (see Chapter 21...

How Is Photogrametry Applied To Hydrology

E., Topographic partition of watersheds with digital elevation models, Water Resour. Res., 22(1), 15-24, 1986. Barrett, E. C., The estimation of monthly rainfall from satellite data, Monthly Weather Rev., 98, 322-327, 1970. Bondelid, T. R., T. J. Jackson, and R. H. McCuen, Estimating runoff curve numbers using remote sensing data, in Proceedings of the International Symposium on Rainfall-Runoff Modeling, Applied Modeling in Catchment Hydrology, Water Resources Publications, Littleton,...

GIS and Digital Terrain Models

Digital terrain modeling is one of the strong areas where GIS has been widely utilized in hydrology. Digital elevation model (DEM) data are employed to derive watershed characteristics such as slope, aspect, curvature, drainage network structure (e.g., Fairfield and Leymarie, 1991), hydrologic response units (HRUs), and also to delineate watershed boundaries (Band, 1986 Jensson and Domingue, 1988 Schultz, 1994). Lozar (1992) delineated drainage paths and watersheds of the entire Earth based on...

Flow Equation For An Unconfined Aquifer

In contrast to confined aquifers, an unconfined aquifer has a free surface (water table) boundary, a boundary at atmospheric pressure. Water released from storage occurs due to gravity drainage as the water table in the aquifer responds to pumping, drainage, or natural or artificial recharge. The unconfined flow problem is commonly analyzed using the Dupuit assumptions (1) uniform and horizontal flow within any vertical cross section, and (2) the velocity at the free surface may be expressed as...

Mass Movement Events

A variety of mass movement events, while strictly not fluvial events, behave in a similar way to floods (Carson, 1976). The gravitationally fueled downhill movement of poorly consolidated regolith results from the introduction of meteoric water that adds weight and decreases hillslope cohesion. These events can do significant damage. Several types of mass movement events are composed of a larger percentage of sediments than a typical stream. Events such as mudflows, or lahars, commonly may...

Nonurban Continental Aerosol

Nonurban continental aerosol is often acidic as a result of anthropogenic sulfate or nitrate. Typical aerosol number concentrations of nonurban continental aerosol are in the range of 103 cm3, with mass concentrations around 30 pg m3 (Anderson et al., 1993). The aerosol mass distribution usually exhibits a trimodal structure similar to that of urban aerosol. Figure 2 shows approximate atmospheric aerosol number concentration N and volume concentration V as a function of altitude z. Because of...

Infiltration Measurement

Infiltration rates can be measured at a point using a variety of methods described here, each appropriate for certain conditions. However, because of the large temporal and spatial variability of infiltration processes, catchment average infiltration rates may be desired, which can be obtained through the water balance analysis of rainfall-runoff observations.31 Ring Infiltrometer. This simple method is most appropriate for flood irrigation or pond seepage infiltration. A cylindrical metal ring...

Ary And Conclusions

Continuing high spatial resolution data from the Landsat and SPOT satellites, passive microwave data from the special sensor microwave imager (SSM I) and continuing meteorological satellite coverage from the NOAA, GOES, GMS, and Meteosat series all mean that the remotely sensed techniques can continue to be employed and expanded upon. New sensors, particularly in the microwave region, promise great potential for hydrologie applications. There are several satellites, such as ERS-1 2 launched by...

Other Pollution Derived Aerosols

Aerosols, both primary and secondary, are generated by a variety of pollution sources in addition to biomass burning these include industrial processes, electric utilities, transportation, construction, and other fuel combustion. While large-scale urban air pollution is a consequence of modern industrial and technological development, smoke produced by indoor fires was perhaps the earliest form of air pollution (Brimblecombe, 1995). It is remarkable that the emissions from many anthropogenic...

Structure Of The Boundary Layer

Boundary layer processes are dominated by the diffusive character of turbulence. This diffusion can be described as a flux of a constituent, which is the rate of transport of the constituent across a surface per unit time and per unit area. Alternatively, it can be expressed as a constituent density times a velocity. Both velocity components and scalars are defined as sums of a mean and a fluctuation, C + Uj and f S + s. The horizontal wind components are commonly defined as and aU1 'V, while...

Sources Of Acidity

Atmospheric acids mainly are produced in the air as a result of complex chemical reactions of the acid precursor gases. Direct emissions of acids such as sulfuric acid, hydrogen chloride, and hydrogen fluoride have been estimated but are not thought to play a significant role in the acidic deposition processes (NAPAP, 1991). Sources of the harmful chemical precursors affecting the acidity of deposited materials can be natural or human caused. The three pollutants of most concern in the acidic...

Flow Equation For A Confined Or Leaky Aquifer

In a confined aquifer, the amount of water released from groundwater storage is dependent on the compressibility of the water and of the porous medium. Confined aquifers are bounded above and below by confining layers. In contrast, leaky or semiconfined aquifers have semipermeable confining layers that are capable of leakage and storage. A multilayered aquifer system is a system in which the aquifers are hydraulically interdependent as changes in head in one layer, caused by pumping, or...

Stratospheric Ozone Observations

The accurate knowledge of the distributions of ozone (03) in the global atmosphere is important for several reasons. First, the amount of ozone in the atmosphere plays a significant role in determining the amount of biologically damaging ultraviolet (UV) radiation that can reach Earth's surface. Second, ozone both absorbs and emits radiation in the atmosphere this must be accounted for in atmospheric circulation models if they are to correctly represent the temperature and wind distributions in...

Old and New Water Contributions to Storm Runoff

There have been many studies in the last 30 years that have made use of the natural geochemical characteristics of runoff to give at least an approximate separation of the storm hydrograph into a contribution from the rainstorm itself (the new water) and water stored in the catchment prior to the event (old water) (see, e.g., Sklash, 1990). Most such studies have used a two-component separation (into old and new water), which requires the assumptions that the geochemical characteristics of the...

Flow Through a System of Rivers

A river system consisting of a main-stem river and one or more tributaries is efficiently solved using an iterative relaxation method (Fread, 1973, 1985) in which the flow at the confluence of the main-stem and tributary is treated as the lateral inflow outflow (q) in Eqs. (29) and (30). This algorithm was extended so as to treat a dendritic system of waterways having nth-order tributaries (Lewis et al., 1996) and further extended to treat a river system that has any bifurcations such as...

Stochastic Simulation Of Precipitation And Streamflow Processes

RAMIREZ, PAOLO BURLANDO, AND ROGER A. PIELKE, Sr. Stochastic simulations of hydroclimatic processes such as precipitation and stream-flow have become standard tools for analyzing many water-related problems. Simulation signifies mimicking the behavior of the underlying process so that realistic representations of it can be made. For this purpose a number of empirical, mathematically physically based, mathematically stochastically based, analog physically based, and...

Storage Routing Models

Significant river improvement projects in the early 1900s provided the impetus for development of an array of simplified flow routing methods. These have been termed storage routing models. They are based on the conservation of mass equation (1) written in the following form in which AS is the change in storage within the routing reach during a At time increment, I 0.5 (r) + I(t + Ai) , and 0 0.5 0(i) + 0(t + Ai) the storage (S) is assumed to be related to inflow (I) and or outflow (O), i.e.,...

Drought Management And Policy Initiatives

Droughts, as shown here, are a regular feature in the tapestry of South African history but have been traditionally managed from an agricultural and conservation perspective (Union of South Africa, 1923). This focus has, however, been expanded during the past decade to include a wider group of affected communities and stakeholders. During the droughts of the 1990s, the impact of the drought on rural populations, for example, was actively monitored by various task forces that emerged from a...

Initial And Boundary Conditions

The most common types of boundary conditions are Dirichlet, Neumann, and Cauchy. 1. Dirichlet conditions occur when a portion of the boundary is at a prescribed head level. For example, if an aquifer is adjacent to a stream or lake, then where j is a known function and 9ilj is the boundary. 2. Neumann conditions occur when a portion of the boundary has a specified flow transversing it normal to the boundary. For example, if a portion of the aquifer boundary is subject to recharge, then where f2...

Arma Model Flowchart

The main challenges in the application of the filter to forecasting of precipitation and streamflow are to define the appropriate matrices and other components of the filter in terms of the hydrologie variables and to estimate them from available data and knowledge of the physical process. In subsequent sections the application of various statistical techniques including the Kalman filter for forecasting hydroclimatic processes, particularly precipitation and...

Precipitation

Precipitation is the process by which liquid and solid-phase aqueous particles, such as rain, snow, sleet, and hail, fall from the atmosphere to Earth's surface. The occurrence of precipitation over land is typically cited as the driving force of the hydrologie cycle, since it triggers the commencement of other fluxes ( vapotranspiration, runoff, infiltration) by providing a new source of moisture to the system. The intensity and frequency of precipitation vary considerably both spatially and...

Snow Hydrology And Water Resources Western United States

Seasonally snow-covered areas of Earth offer special challenges for water resources management, challenges that arise from both hydrologic and social factors. Seasonal snowpacks account for the major source of the runoff for streamflow and groundwater recharge over wide areas of the midlatitudes. For example, in the western United States over 85 of the annual runoff from the Colorado River basin originates as snowmelt. Most of this is from a few small source areas in four western states, mostly...

[Saq Hsps Hsxspilm

Where Hs is the Henry's law solubility coefficient of the gas. (In practical units, ps in bar and S(aq)J in mol L, i.e., M, Hs has units M bar.) Abundance of a gas-phase species is expressed in terms of the molar mixing ratio in air x, which is applicable equivalently to substances in gas, aerosol, or solution phases (Schwartz and Warneck, 1995). Characterization of the Henry's law solubility is the first step to understanding the uptake and reaction of a gas in cloudwater. Henry's law...

Introduction

Some trace gases and pollutants are readily removed from the atmosphere by becoming incorporated into cloudwater and then falling to Earth's surface in precipitation. In cloud-free air, small amounts of condensable species such as sulfates, ammonia, and nitrates coagulate with water vapor to form or nucleate extremely small atmospheric aerosol particles. Through gaseous diffusion and aerosol coagulation, smaller aerosols generally grow in size with time, while continuously maintaining an...

Visibility Impairment

Aerosols introduced into the atmosphere can result in visibility impairment that is manifested in two distinct ways first, as a general alteration in the appearance of landscape features such as color, contiguous contrast between adjacent geologic features, etc., and secondly the aerosol haze may become visible in and of itself. Haze may be visible by the contrast or color difference between itself and its background, or (at great enough optical depths) uniform haze manifests itself as a sem...

The Hydrologic Cycle

Figure represents a conceptual model of the hydro logic cycle and shows Earth's water movement between the ocean, land, and atmosphere. As with all cycles, it is ongoing and continuous, and there is no specific start or end point however, because the main focus of this handbook is meteorology, precipitation is an appropriate place to begin an evaluation. Precipitation is water released from the atmosphere in the form of rain, snow, sleet or hail. During precipitation, some of the moisture is...

Residence Times Of Particles In The Troposphere

Particles are eventually removed from the atmosphere by two mechanisms deposition at Earth's surface, so-called dry deposition, and scavenging by droplets, so-called wet deposition (Seinfeld and Pandis, 1998). Because wet and dry deposition lead to relatively short residence times in the troposphere and because the geographical distribution of particle sources is highly nonuniform, tropospheric aerosols vary widely in concentration and composition over Earth. Whereas atmospheric trace gases...

Introduction Defining Runoff

Runoff Generation Process

There are a number of different definitions of runoff that have been used either explicitly or implicitly in hydrological analyses over the years. In what follows we will use a working definition that runoff is that part of the rainfall falling on a catchment area that eventually leaves the catchment as a surface streamflow, whatever the flow pathway that the water has followed on its way to the stream channel. Thus this definition includes both surface and subsurface runoff pathways. Dunne...

The Paranparaguay River Basin Interannual Variability And Extreme Events

The Paran -Paraguay River Basin in South America encompasses about 84 of the La Plata Basin with a population of about 100 million (1992 figures). It is the most developed agricultural and industrial zone in South America, accounting for 80 of the economic production in Argentina, Brazil, and Paraguay. The period of relatively small numbers of high floods between 1905 and 1960 coincided with the expansion of urban areas onto the valley bottoms. Three major changes have taken place in the basin...

The Nile Centuries Of Change

The Middle East region, taken here to include the Tigris-Euphrates, the Jordan, and the Nile River Basins, has some of the highest population growth rates in the world and has a heavy reliance on irrigation for agricultural productivity. The region also has diverse historical religious, ideological, and ethnic disputes. Political friction and water scarcity have combined to produce perhaps the most volatile situation in the world (McCaffrey, 1993). At present, only the Tigris-Euphrates system...

Thomas E Downing And Yolande Stowell

Climate affects food security in two distinct ways. Primarily, climate in association with soils, terrain, and vegetation is a resource that influences potential agricultural production. Agricultural productivity, in turn, provides income to individuals and households, leads to investment in infrastructure, and fuels the regional economy. Climate also includes the hazards of drought, flood, windstorms, hail, and temperature extremes. Such climatic hazards lead to direct losses of income,...

Ammonia Oxidation

A poorly quantified, but still potentially important source of NO, is the oxidation of atmospheric ammonia (NH3). A major uncertainty regarding this source is the lack of information on the tropospheric distribution of NH3. NH3 is initially oxidized by OH to form NH2. NH2 may go on to form NO, through reaction with 03, however, it may also react with NO, to form N2 or N20. Based on differences in rate coefficients, NH3 oxidation should provide a net source of NO, when ambient NO, is less than...

Methodology For Impact Assessment Of Climate Change Scenarios

Unlike assessments of current and historical events, impact assessment of projected climate change is based on scenarios, or plausible pictures of the future. This kind of research can include analysis of past observed events (e.g., the Dust Bowl in the United States during the 1930s), which could serve as societal analogs of a future warm climate (Glantz, 1988), or as climate change analogs superimposed on twenty-first-century society (Rosenberg, 1993), but there are also many studies at...

Snow Hydrology

Model From Synthetic Soil

Snow is a form of precipitation in hydrology it is treated somewhat differently because of the lag between when it falls and when it produces runoff and groundwater recharge, and is involved in other hydrologic processes. Remote sensing is a valuable tool for obtaining snow data for predicting snowmelt runoff as well as climate studies. Nearly all regions of the electromagnetic spectrum provide useful information about the snowpack. Depending on the need, one may like to know the areal extent...

Harrison 1986 Simulating Drought In Sa Reference

Abrams, L., Drought policy water issues, The African Water Page, http www.african- water.org.drghtwater.htm 1997. Abrams, L., R. Short, and J. Evans, Root cause and relief restraint report, National Consultative Forum on Drought, Secretarial and Ops Room, Johannesburg, October 8, 1992. Adams, L., A rural voice, strategies for drought relief, Indicator S. Afr., 10(4), 41-46, 1993. Alexander, W. J. R, Floods, droughts and climate change, S. Afr. J. Sci., 91, 403 08. Allan, R. J, J. A. Lindesay,...

Impacts Of Droughts In South Africa

Drought impacts, however, are not the result only of insufficient rainfall or searing temperature. In most cases, drought impacts are the outcome of the interaction of a number of social and other human factors that can heighten the vulnerability of communities and various exposure units (e.g., vegetation) and reduce resilience of society and ecosystems to the natural hazard (Dilley, 2000 Vogel et al, 2000). As a result of these components of drought, a number of impacts are recorded. The scale...

What Is Enso

The El Ni o-Southern Oscillation (ENSO) is a coupled atmospheric-oceanic phenomenon that has global manifestations and recurs approximately every 2 to 10 years. The atmospheric component of ENSO is the Southern Oscillation, an interannual seesawing of sea-level atmospheric pressure anomalies between northern Australia (Darwin) and the southeast Pacific (near Tahiti). There is both a warm phase (El Ni o) and a cold phase (La Ni a). The warm phase involves an extensive warming of the upper ocean...

Fundamentals Of Visibility

A definition of visibility, as it relates to management of the many visual resources found in national parks, wilderness areas, and urban centers, is a complex and difficult concept to address. Should visibility be defined in strictly technical terms that concern themselves with exact measurements of illumination, threshold contrast, and precisely measured distances Or is visibility more closely allied with value judgments of an observer viewing a scenic vista Historically, visibility has been...

Hydrologic Modeling For Runoff Forecasting

The problem of forecasting streamflow levels given precipitation data has received the time and attention of a great many hydrologists. Models developed for this purpose have ranged from simple to extremely complex. The simplest ones are based on input-output regression-type relationships, while the most complex ones attempt to represent the detailed water and energy balance physics occurring in the watershed. The complex models are motivated largely by experimental evidence that the...

Kinematic Wave Model

The most simple type of distributed hydraulic routing model is the kinematic wave model. It is based on the following simplified form of the momentum equation (2) in which S0 is the bottom slope of the channel (waterway) and a component of the term, dh dx dy dx S0, in which dy dx is assumed to be zero. This assumes that the momentum of the unsteady flow is the same as that of steady, uniform flow described by the Manning equation or a similar expression in which discharge is a single-valued...

Saint Venant Equations

A modified and expanded form (Fread, 1988, 1992) of the original one-dimensional Saint-Venant equations (1) and (2) consist of the conservation of mass equation, i.e., dQ dx + dsc(A + A0) dt -q 0 (29) o smQ) dt + d(PQ2 A) dx + gA(dh dx + Sf + S + + L + WfB 0 (30) where Q is discharge, h is the water-surface elevation, A is the active cross-sectional area of flow, A0 is the inactive (off-channel storage) cross-sectional area, sr and sm are area-weighted and conveyance-weighted sinuosity factors,...

Implicit Four Point Finite Difference Approximations

The extended Saint-Venant equations (29) and (30) constitute a system of partial differential equations with two independent variables, x and t, and two dependent variables, h and Q, the remaining terms are either functions of x, t, h, and or Q, or they are constants. The partial differential equations can be solved numerically by approximating each with a finite-difference algebraic equation then the system of algebraic equations are solved in conformance with prescribed initial and boundary...

Impacts Of Stratospheric Ozone Depletion

In 1928, Charles Kettering and Thomas Midgley, Jr., scientists with General Motor's Research Corporation in Dayton, Ohio, invented chlorofluorocarbons (CFCs) as a safe alternative to toxic and flammable refrigerants. In 1974, Mario Molina and F. Sherwood Rowland published a paper in Nature that linked the use of CFCs to destruction of Earth's stratospheric ozone layer. Today, the international community has made substantial progress toward phasing out the production and consumption of CFCs and...

Acid Rain And Deposition

The first mention of acid rain in print was by Robert Boyle in which he referred to nitrous or salino-sulphureous spirits in air in his 1692 book A General History of the Air. The Scottish chemist Robert Angus Smith began to study acid rain in Manchester, England, in 1852 and extended the work in England, Scotland, and Germany for 20 years. His 1872 book, Air and Rain The Beginnings of a Chemical Climatology, pointed out the link between sulfur pollution and acid rain. He warned that acid rain...

General Features Of Photochemical Smog Diurnal and Seasonal Cycle

Mexico City Voc Nox

Ozone and other secondary reaction products show a pronounced diurnal cycle with peak concentrations typically occurring in late afternoon. The diurnal cycle of 03 shows a sharp contrast with the diurnal cycle of primary species, including NOx, HC, and CO (see Fig. 1). The primary species typically have peak concentrations in early morning and much lower concentrations during the daytime as concentrations are diluted through the process convection-driven vertical mixing. Because production of...

Biophysical Dimensions Of Drought In South Africa

South Atlantic Anticyclone

Several factors interact to produce the climate and weather of South Africa (for good overviews see Tyson, 1986 Mason and Jury, 1997 Lindesay, 1998 Tyson and Preston-Whyte, 2000). The physical location of the country in the subtropics shapes climate and weather (Fig. 1). The local orography and landscape features of the country (most of the country is situated on a plateau approximately 1500 m above mean sea level) and sea surface temperatures (SSTs) of the cooler Atlantic and warmer Indian...

I11

Figure 9 Comparison of correlation function for monthly rainfall (from Kang and Ramirez46). See ftp site for color image. scale environment. Being able to parameterize the scaling characteristics of precipitation as a function of such variables is a prerequisite for implementing of down-scaling methodologies based on random cascades. Perica and Foufoula-Georgiou77 introduced a spatial downscaling scheme that is able to statistically reproduce the spatial heterogeneity of observed precipitation...

Approaches To Coping Capacity And Vulnerability

Causes Destitute

The three case studies highlight diverse situations and ways in which households have coped with climatic variations and other stresses. A rich literature now exists on coping strategies, capacity to withstand shocks and stress, and more generally vulnerability. A few observations on vulnerability frameworks are now presented as an introduction to the following section, which specifically addresses the intersection of vulnerability and climate prediction. Vulnerability can be defined as the...

Causes Of Droughts In South Africa

Having described the pattern of rainfall-producing systems in the country, attention now focuses on some of the causes of periods of insufficient rainfall and droughts. The forcing mechanisms for droughts are well documented for the southern African region (see, e.g., Tyson, 1986 Mason and Jury, 1997 Lindesay, 1998 Tyson and Preston-Whyte, 2000). Much of the recent research in the country has focused on the prolonged droughts of the last two decades (namely the 1980s and 1990s) Tyson and Dyer,...

GIS and Hydrologic Models

Digitized Images Gis

Watershed database development usually is the first important stage in a hydrologic modeling study. Remotely sensed data might be employed to generate thematic maps and also to serve as map basis when no other reliable data are available. Landsat TM and SPOT images data are suitable for production of digital map at scales ranging from 1 50,000 to 1 100,000 (Welch et al., 1985 Swann et al., 1988 Gugan and Dowman, 1988 Konecny et al., 1988). Base maps, produced from remote sensing and integrated...

Pm

Where Vs L3 is the total volume of soil, F, L3 is the volume of air, Vw L3 is the volume of water, and pm ML3 is the particle density normally about 2.65 g cm3 . The volumetric water content, or soil moisture, 0 L3L 3 is the ratio of water volume to soil volume where M is the weight of water, Wd M is the weight of dry soil, and pK M L3 is the densiw of water. Soil moisture can vary in both time and space, w ith a theoretical range from 0 to lt p, but for natural soils the range is significantly...

Stochastic Forecasting Of Precipitation And Streamflow Processes

VAL D S, PAOLO BURLANDO, AND JOS D. SALAS Over the past two decades, considerable research has been carried out in hydrology on developing mathematical tools and approaches for short- and long-term precipitation and streamflow forecasting. The forecasts may be concerned with flood warning, flood control, water quality control, navigation, energy production, and irrigation. Hydrologie forecasting signifies estimating the time of occurrence and the magnitude of a hydrological event before...