Preface

Droughts, floods, heatwaves, and other extreme weather events often have disastrous consequences for society and for the infrastructure that provides our goods and services. An increasing global population and an increasing population occupying areas subject to extreme weather events has heightened awareness of the potential impact of climate and weather and extreme events on our daily lives. This new awareness is occurring at a time when a consensus in the scientific community supports the...

Satellites

Meteorological satellites provide images and quantitative information about surface features and the lowest 20 km of the atmosphere (WMO, 1996). The contribution of satellite data to hydroclimatology has expanded greatly since the United States launched the Television and Infrared Observation Satellite (TIROS-1) in April 1960 to open the weather satellite era. Early satellites were limited to providing basically cloud images, but by the 1980s reliable measurements of net incoming and outgoing...

Estimating areal hydroclimatic data

For many hydroclimatic applications, a significant problem arises concerning the use of point sensors for climate data and data extrapolation away from the instrument site. This is often expressed as the representative area and is of considerable importance in hydroclimatology. Different physical factors influence determination of the representative area for a given variable. Gridding and remote sensing techniques provide alternative approaches for developing areal hydroclimatic data estimates,...

Rainfall remote sensing

Practical limitations of in situ observation networks for measuring spatially averaged precipitation over large and inaccessible areas have promoted the use of remote sensing to quantify precipitation. Both radar and satellites are important contributors to providing real-time precipitation measurements for large areas. Meteorological radars have a spatial resolution of 1-2 km and temporal revisit times of 15-30 minutes. Satellite remote sensing products have a spatial resolution of 10-20 km...

Snow remote sensing

Remote sensing of snow involves detection and quantification of falling snow, assessment of snowcover on the land, and the snow water equivalent SWE of the snowpack. Detection of falling snow and assessment of the snow-pack require different approaches and remote sensing strategies. Quantification of falling snow has real-time applications for transportation, construction, agriculture, and commerce, and snowcover data are used for flood forecasting, water resources management and planning, and...

Recent precipitation trends

Rain and snow are pivotal variables in the hydrologic cycle, but reliable estimates of global precipitation are difficult to achieve. An obvious contributor to the difficulty in achieving accurate quantitative documentation of global precipitation is that precipitation is discontinuous in time and space. The variation in the spatial character of precipitation is exacerbated by the fact that most oceanic and unpopulated land areas are inadequately represented in existing data Xie and Arkin, 1997...

Emergence of the hydrologic cycle

An early record of the importance of water for human life can be found in Genesis, the first book of the Bible. In this account of creation, light is provided on day one by the Sun, Moon, and stars. Separation of waters below the sky from waters above it occurs on day two, and day three begins with the separation of land and oceans. Contemporary thought recognizes that energy from the Sun warms the Earth and water dominates the distribution of heat over the planet Langenberg, 2002 , and the...

Treering reconstructions

The use oftree rings to reconstruct hydroclimate is called dendroclima-tology and dendrohydrology. Most temperate forest trees display concentric annual deposits of tree trunk material forming alternating lighter and darker bands of seasonal growth increments around the tree's circumference. The annual couplets of earlywood and latewood comprise an annual growth increment known as a tree ring Fig. 8.1 . The mean ring width in any tree is a function of tree species, tree age, nutrients available...

Regional hydroclimate

California Physical Features

The Earth's surface can be divided into regions that have similar hydroclimates due to the global climate system, but regional hydroclimate variations elucidate the role of a second tier of factors responsible for the spatial variation in hydroclimate when viewed at a higher resolution than global patterns. Regional hydroclimates emerge as identifiable entities based on latitude, altitude, and orientation of the surface in relation to water bodies, mountains, and prevailing winds Hartmann, 1994...

Recent streamflow trends

Rivers integrate the hydroclimatic variables within the watershed they drain. Streamflow results from the interaction of the hydroclimatic variables in both time and space, and watershed physiography exerts temporal influences on transformation of the residual precipitation into streamflow in a specific drainage basin. Precipitation and temperature are major climatic factors determining runoff, and both are influenced by ocean-atmosphere processes to produce streamflow variability on...

Streamflow

Streamflow is the flow rate or discharge of water at a specified location on a natural stream channel. In general terms, streamflow is the residual of the precipitation that falls on the area upstream of the selected stream channel reference point. The dominantly horizontal character of streamflow establishes its roles in climate of the first kind and the terrestrial branch of the hydrologic cycle as the transfer function for returning excess continental liquid moisture to the oceans....

Selective atmospheric response to solar radiation

Diagram Triatomic Molecule H2o

Radiant energy arriving from the Sun can be traced through all of the energy transfers and transformations that embrace hydroclimatology. As the photons penetrate the Earth's atmosphere, they are transmitted through the gaseous envelope, or they are reflected or absorbed by gases, particulates, clouds, and water droplets. The reflected photons constitute a major component of the Earth-atmosphere albedo. The photons absorbed by atmospheric gases are surprisingly small in number. The relatively...

Interception

All of the rainfall on a surface covered by vegetation may not reach the ground beneath the plants. Depending on the nature of the rainfall and the character of the plant canopy, some water may be retained on the plant's surface. The retention of incident rainfall on the leaves and branches of plants is called interception see Fig. 6.1 . Most of the interception occurs at the beginning ofstorms. Evaporation ofintercepted water results in the interception loss, which can be a significant...

The radiation balance

Atmospheric Energy Equilibrium

The major forcing for the climate system is energy received from the Sun. The Earth intercepts a fraction of the radiant energy emitted by the Sun. A surface perpendicular to the solar ray at the upper edge of the Earth's atmosphere and at the mean Earth-Sun distance receives 1367Wm 2 or the solar constant Sc , but its true value is uncertain by 4Wm 2 Hoyt and Schatten, 1997 . The solar radiation spread evenly over the spherical surface of the entire globe equates to 342 W m 2. This...

Global radiation balance

The radiation balance is a global phenomenon. The flows of radiant energy into and out of the upper edge of the Earth's atmosphere are approximately equal over a time scale of several years. This equilibrium state is the expected behavior for the climate system and a stable climate. The fluxes of energy may not balance over shorter periods, or a perturbation in the system may cause the climate system to seek a new equilibrium state. Whatever the condition of the global climate system,...

Surface radiation balance

At the Earth's surface, the concept of net radiation is a useful paradigm. In its simplest form, net radiation is expressed as Rn K KT L L 2.11 where Rn is net all-wave radiation, K is incoming shortwave solar radiation, K is the outgoing shortwave radiation or the albedo of the surface, L is the longwave emission from the atmosphere directed downward to the Earth, and L is the longwave emission from the Earth's surface. On an annual basis, Figure 2.3 shows that the Earth's surface is a net...

Radiosonde upperair measurements

Upper-air climatology is less well known than surface conditions, but upper-air observations provide direct measurements of atmospheric state variables above the Earth's surface. These measurements are an important complementary data source for understanding atmospheric circulation and its transport of energy and mass. The upper-air data provide a vertical dimension that reveals the atmospheric response to time and space variations required to maintain energy, mass, and momentum balances and...

The global hydrologic cycle

Global Hydrologic Cycle

The global hydrologic cycle is a logical unifying theme for hydroclima-tology. For practical purposes, the global hydrologic cycle is a closed circulation for water's three phases. Within the structure of the general systems perspective commonly employed in the earth sciences, the hydrologic cycle is a subsystem and centerpiece of the global climate system. Consequently, the occurrence and movement of water assumes a primary role in both climatology and hydrology even though some illustrations...

The hydrograph

Wetland Hydrograph

Streamflow is a valuable source of hydroclimatic information. It conveys the complex details of how the climate system and the hydrologic cycle are interacting. The runoff process can be viewed directly for relatively small areas, but streamflow for a large watershed results from distant events and relationships not readily apparent. It is necessary to understand how water arrives at the stream channel in order to assess the coupling of climate and the hydrologic response. Streamflow is...

Atmospheric pressure

Atmospheric transport that is central to climate of the first kind and the atmospheric branch of the hydrologic cycle is accomplished by the response of the Earth's atmosphere to pressure distributions. The dynamically changing distribution of atmospheric pressure is in response to the principles of energy, mass, and momentum conservation underlying the vertical and horizontal pressure gradients that set the atmosphere in motion. Measuring atmospheric pressure at the surface is essential for...

Terrestrial radiation and the greenhouse effect

About one-half of the solar radiation reaching the upper edge of the Earth's atmosphere is ultimately absorbed by the Earth's surface see Fig. 2.3 . The longwave infrared radiation emitted by the Earth's surface has an important role in the climate system because it provides the largest quantitative energy input to the atmosphere. Atmospheric gases that are transparent to shortwave solar radiation are largely opaque to longwave terrestrial radiation that occurs at wavelengths greater than 4.0...

Rainfall runoff

The streamflow responses to rainfall and snowmelt produce identifiable differences in discharge hydrographs. Rainfall events produce streamflow dominated by surface runoff and or near-surface flow. These conditions can produce abrupt increases in streamflow, especially for small watersheds or urbanized watersheds. Land use and geology can delay runoff and produce less abrupt streamflow increases and more gradual decreases. The climatic role in the runoff process is characterized by the path...

Two climates for two hydrologic cycles

Sketches Hydrologic Cycle

Contemporary hydroclimatology recognizes that the atmosphere has a central role in delivering moisture to a specific location. In addition, the atmosphere provides the climatic framework for the Earth's surface energy and moisture fluxes and balances that drive the hydrologic cycle. Understanding the role of these components is required for a comprehensive view of hydroclimatology that extends beyond the traditional context of climatology and beyond the boundaries of hydrometeorology. A dynamic...

Hydroclimatology defined

The American hydrologist Walter Langbein 1967 defined hydroclimatology as the study of the influence of climate upon the waters of the land. He identified precipitation and evapotranspiration and the imbalance of these climatic elements as the focus of hydroclimate. However, subsequent advances in understanding natural processes complemented by development of contemporary measurement techniques, data acquisition, and analytical tools suggest this perspective is too restrictive for modern...

Factors affecting runoff

Factors Affecting Run Off

It is generally recognized that runoff from a given watershed is influenced by two major groups of factors categorized as climatic and physiographic. These factors are evident in the form of Equation 6.1 with the climatic factors, precipitation and evapotranspiration, on the left side and the variables on the right side being related to physiographic factors. However, this is not an exclusive listing of the variables, but rather it is a synthesis of the influence of climatic and physiographic...

Radiation

The driving force for the Earth's hydroclimate is the supply of radiant energy from the Sun. Climate of the first kind and the atmospheric branch of the hydrologic cycle are intimately coupled with the character of solar radiation, how the Earth's atmosphere and surface respond to the incoming solar radiation, and how the Earth and atmosphere radiate energy to space. Measuring these energy fluxes is an important step in defining their time and space variations and understanding how they drive...

Planetary energy balance

At the Earth's surface, positive quantities of radiant energy are available to be transformed into non-radiative energy forms. These non-radiative energy transfers are important components in helping to maintain the energy balance of the Earth-atmosphere system as shown in Figure 2.3. The largest portion of radiant energy absorbed at the Earth's surface is used to evaporate water. The radiant energy is transformed into latent heat, which is attached to the water molecules and travels with them...

Remote sensing data

Technology has provided an expanding array of alternative approaches for acquiring hydroclimatic data using instruments at a distance from the location being measured. The practice of distant measurement known as remote sensing is accomplished using instruments on satellites, aircraft, or ground-based. In most cases, the remote sensing technique involves the interaction of electromagnetic radiation with the Earth's surface or the atmosphere. Aerial photography utilizing visible wavelengths of...

Infiltration

The first raindrops that reach the soil surface either directly or as through-fall enter the soil profile through the pores and openings in the surface by infiltration. This process is driven by capillary forces and by gravity as discussed in Section 4.7. Capillary forces draw the water into the smaller pores of the soil matrix, but this movement of water is relatively slow and the quantity is small. Gravity moves water through the larger openings at a faster rate and in greater quantities....

Evaporation and evapotranspiration

Stilling Well Evapori

Evaporation from free water surfaces and bare soil and evapotranspiration from vegetated surfaces support upward directed energy and mass fluxes that complement downward directed precipitation in climate of the second kind and the terrestrial branch of the hydrologic cycle. Furthermore, evaporation and evapotranspiration have an important role in determining surface temperatures, surface pressure, rainfall, and atmospheric motion. The upward directed energy and water vapor fluxes from the Earth...