WATER RESOURCES AND CLIMATE CHANGE
Vijay P. Singh
1 and Qiang Zhang
2
1
Department of Biological and Agricultural Engineering,
Texas A&M University, College Station, TX, USA
2
Department of Water Resources and Environment,
Sun Yat-sen University, Guangzhou, China
Synonyms
Hydrometeorology
Definitions
Hydrology is the study of space-time characteristics of the
quantity and quality of the water on earth. It includes the
occurrence, movement, distribution, circulation, storage,
exploration, development, and management of water in
space, time, and frequency domains. Hydrology is
partitioned into surface water hydrology, groundwater
hydrology, snow and glacial hydrology, and atmospheric
hydrology or hydrometeorology.
The hydrologic cycle is the continuous movement of
water between the atmosphere, biosphere, pedosphere,
lithosphere, and hydrosphere. It is the core of hydrologic
research.
Water resources refer to the water stored in any form on
the earth surface and in the atmosphere, biosphere,
pedosphere, and lithosphere. More specifically, water
resources are the waters feasible for human use (their
quantity and quality) that can be renewed within
a reasonable time interval.
Hydrologic cycle
Evaporation is the only hydrologic component connecting
water balance and energy balance and is the key
component in understanding the hydrologic cycle
(Xu and Singh, 2005). Xu et al. (2006) summarized the
terms describing evaporation in the literature: (1) free
water evaporation, ET o , represents the amount of evaporation from open/free water surface; (2) actual evapotranspiration, ET a , describes all the processes by which liquid
water at or near the land surface becomes atmospheric
water vapor under natural conditions; and (3) potential
evapotranspiration, introduced in the late 1940s and
1950s by Penman (1948, 1956), is defined as “the amount
of water transpired in a given time by a short green crop,
completely shading the ground, of uniform height and
with adequate water status in the soil profile.” Reference
evapotranspiration (ET ref ) (Allen et al., 1998) is defined
as “the rate of evapotranspiration from a hypothetical
reference crop with an assumed crop height of 0.12 m,
a fixed surface resistance of 70 s m
À1 and an albedo of
0.23, closely resembling the evapotranspiration from an
extensive surface of green grass of uniform height,
actively growing, well-watered, and completely shading
the ground.” Evapotranspiration is perhaps the most
difficult of all the hydrologic components in the hydrologic cycle due to complex interactions among the components of the land-plant-atmosphere system (Xu and Singh,
2005; Zhang et al., 2011b).
It is widely expected that the increasing average global
temperature will increase evaporation of terrestrial water
bodies. However, many studies have found decreased
pan evaporation and ET ref (e.g., Roderick and Farquhar,
2002), which is usually called the pan evaporation paradox. Global warming has the potential to alter the hydrologic cycle and therefore cause uneven distribution of
water resources. Hydrologists and meteorologists suggest
that an increase in surface temperature can result in higher
evaporation rates and enable the atmosphere to transport
higher amounts of water vapor which, in turn, leads to
an accelerated hydrologic cycle (e.g., Menzel and Bürger,
2002). Warmer temperatures increase the capacity of the
atmosphere to hold water vapor causing greater probability of high-intensity rainstorms, hence triggering flood
and drought conditions. Global warming therefore may
result in an increase in intensity of extreme events
(WMO, 2003) and the uncertainty of water supply at
regional and global scales.
Climate changes and weather extremes
Climate change reflects changes in the statistical distributions of weather components at various time scales ranging from seconds to millions of years. The weather
components include precipitation, temperature, evaporation, relative humidity, and so forth. The causes behind
climate change can be oceanic and biotic processes, solar
radiation changes, plate tectonics and volcanic eruptions,
and also human-induced alterations of natural processes.
Climate change is sometimes referred to as global
warming which can cause different hydrologic responses
at different spatial and temporal scales.
A trend of decreasing rainfall has been documented in
the Mediterranean area (Karl, 1998), and significant
decreasing extreme rainfall has also been observed in
Western Australia (Haylock and Nicholls, 2000).
However, some researchers have found increasing
extreme precipitation in the United States (e.g., Kunkel,
2003). Others have reported no trend in extreme rainfall
in Canada (Zhang et al., 2001). Zhang et al. (2011a) also
indicated changing characteristics of precipitation across
China. Generally, a wet tendency has been noted in south
China, a slight wet tendency in northwest China, and a dry
tendency in north China. Further, increasing precipitation
intensity has been witnessed mainly in the lower Yangtze
River and the Pearl River basins.
Analyzing wet periods and the associated precipitation
intensity over Europe, Zolina et al. (2010) indicated that
longer wet periods and higher intensities should have
a significant impact on the terrestrial hydrologic cycle,
including subsurface hydrodynamics, surface runoff, and
WATER RESOURCES AND CLIMATE CHANGE
731
Vijay P. Singh
1 and Qiang Zhang
2
1
Department of Biological and Agricultural Engineering,
Texas A&M University, College Station, TX, USA
2
Department of Water Resources and Environment,
Sun Yat-sen University, Guangzhou, China
Synonyms
Hydrometeorology
Definitions
Hydrology is the study of space-time characteristics of the
quantity and quality of the water on earth. It includes the
occurrence, movement, distribution, circulation, storage,
exploration, development, and management of water in
space, time, and frequency domains. Hydrology is
partitioned into surface water hydrology, groundwater
hydrology, snow and glacial hydrology, and atmospheric
hydrology or hydrometeorology.
The hydrologic cycle is the continuous movement of
water between the atmosphere, biosphere, pedosphere,
lithosphere, and hydrosphere. It is the core of hydrologic
research.
Water resources refer to the water stored in any form on
the earth surface and in the atmosphere, biosphere,
pedosphere, and lithosphere. More specifically, water
resources are the waters feasible for human use (their
quantity and quality) that can be renewed within
a reasonable time interval.
Hydrologic cycle
Evaporation is the only hydrologic component connecting
water balance and energy balance and is the key
component in understanding the hydrologic cycle
(Xu and Singh, 2005). Xu et al. (2006) summarized the
terms describing evaporation in the literature: (1) free
water evaporation, ET o , represents the amount of evaporation from open/free water surface; (2) actual evapotranspiration, ET a , describes all the processes by which liquid
water at or near the land surface becomes atmospheric
water vapor under natural conditions; and (3) potential
evapotranspiration, introduced in the late 1940s and
1950s by Penman (1948, 1956), is defined as “the amount
of water transpired in a given time by a short green crop,
completely shading the ground, of uniform height and
with adequate water status in the soil profile.” Reference
evapotranspiration (ET ref ) (Allen et al., 1998) is defined
as “the rate of evapotranspiration from a hypothetical
reference crop with an assumed crop height of 0.12 m,
a fixed surface resistance of 70 s m
À1 and an albedo of
0.23, closely resembling the evapotranspiration from an
extensive surface of green grass of uniform height,
actively growing, well-watered, and completely shading
the ground.” Evapotranspiration is perhaps the most
difficult of all the hydrologic components in the hydrologic cycle due to complex interactions among the components of the land-plant-atmosphere system (Xu and Singh,
2005; Zhang et al., 2011b).
It is widely expected that the increasing average global
temperature will increase evaporation of terrestrial water
bodies. However, many studies have found decreased
pan evaporation and ET ref (e.g., Roderick and Farquhar,
2002), which is usually called the pan evaporation paradox. Global warming has the potential to alter the hydrologic cycle and therefore cause uneven distribution of
water resources. Hydrologists and meteorologists suggest
that an increase in surface temperature can result in higher
evaporation rates and enable the atmosphere to transport
higher amounts of water vapor which, in turn, leads to
an accelerated hydrologic cycle (e.g., Menzel and Bürger,
2002). Warmer temperatures increase the capacity of the
atmosphere to hold water vapor causing greater probability of high-intensity rainstorms, hence triggering flood
and drought conditions. Global warming therefore may
result in an increase in intensity of extreme events
(WMO, 2003) and the uncertainty of water supply at
regional and global scales.
Climate changes and weather extremes
Climate change reflects changes in the statistical distributions of weather components at various time scales ranging from seconds to millions of years. The weather
components include precipitation, temperature, evaporation, relative humidity, and so forth. The causes behind
climate change can be oceanic and biotic processes, solar
radiation changes, plate tectonics and volcanic eruptions,
and also human-induced alterations of natural processes.
Climate change is sometimes referred to as global
warming which can cause different hydrologic responses
at different spatial and temporal scales.
A trend of decreasing rainfall has been documented in
the Mediterranean area (Karl, 1998), and significant
decreasing extreme rainfall has also been observed in
Western Australia (Haylock and Nicholls, 2000).
However, some researchers have found increasing
extreme precipitation in the United States (e.g., Kunkel,
2003). Others have reported no trend in extreme rainfall
in Canada (Zhang et al., 2001). Zhang et al. (2011a) also
indicated changing characteristics of precipitation across
China. Generally, a wet tendency has been noted in south
China, a slight wet tendency in northwest China, and a dry
tendency in north China. Further, increasing precipitation
intensity has been witnessed mainly in the lower Yangtze
River and the Pearl River basins.
Analyzing wet periods and the associated precipitation
intensity over Europe, Zolina et al. (2010) indicated that
longer wet periods and higher intensities should have
a significant impact on the terrestrial hydrologic cycle,
including subsurface hydrodynamics, surface runoff, and
WATER RESOURCES AND CLIMATE CHANGE
731