Hydroclimate Projects

Radiosonde upperair measurements

Global Radiosonde Graph

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...

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...

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...

The radiation balance

Mean Annual Global Radiation Map

The simplest form of the global radiation balance is portrayed in Figure 2.3. Details of the spatial characteristics of the radiation balance are provided by observational and remote sensing data discussed in Chapters 3, 4, and 5. The radiation balance at the top of the Earth's atmosphere and the radiation balance at the Earth's surface are important to hydroclimatology because they emphasize the unequal distribution of energy that is the primary forcing for the climate system. Furthermore, the...

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...

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...

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...

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...

Reservoirs and streamflow

Reservoirs are artificial lakes produced by dams that impede streamflow. They function like lakes in almost all respects, but reservoirs are located by human design and are usually operated to achieve multiple goals. Reservoirs mimic natural lakes regarding their hydroclimatic influences on water storage and evaporation, and their water balance is expressed by Equation 6.14. However, flow regulation is more evident with reservoirs as the storage volume is managed to accommodate flood control,...

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...

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...

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...

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...

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...

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...

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...

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...

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...

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...

Water as a unifying concept

Water is an essential resource for humans and for natural ecosystems. Satellite images of the Earth show convincing evidence of an abundance of water on the planet. Unfortunately, only a small percentage of the total water volume is available as freshwater suitable for humans and many natural ecosystems. The relatively small volume of freshwater is further constrained by an uneven distribution over the globe that is paradoxical to the image of Earth as a water planet. Approximately one-third of...

Floods The Hydroclimatic Extreme Of Excessive Moisture

1 The realm of hydroclimatology 1 1.1 Water as a unifying concept 1 1.2 The global hydrologic cycle 5 1.4 Emergence of the hydrologic cycle 8 1.5 Two climates for two hydrologic cycles 14 1.7 Data quality 21 Review questions 23 2 The climate system and the hydrologic cycle 24 2.5 The atmospheric subsystem 30 2.9 Selective atmospheric response to solar radiation 39 2.10 Terrestrial radiation and the greenhouse effect 43 2.11 Global radiation balance 45 2.12 Surface radiation balance 47 2.13...

Dynamic climate

Global climate has changed through time and continues to change and to display variability (Burroughs, 2001 Lockwood, 2001). Both climate change and variability can be a response to internal or external forcing of the climate system. Passive forcings involve modulation of faster responding components by slower response time components. Active forcings result from variations and instabilities of the climate system dynamics and by coupled interactions between climate system components. Passive...

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,...

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...

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...

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...

Climate and water

Climate variability directly impacts the water resource and has stimulated expanding interest in the scientific study of the global hydrologic cycle. Water is a fundamental aspect of most people's lives in humid regions where its supply is taken for granted, but water is highly valued in supply-limited arid regions. The prospect of climate change and an altered water supply imposes a broadened dimension for everyone to understand the relationships among climate, the hydrologic cycle, and the...