Geoscience Reference
In-Depth Information
• Climate Variability and Predictability (CLIVAR): CLIVAR's mission is to observe,
simulate and predict the Earth's climate system with a focus on ocean-atmosphere
interactions in order to better understand climate variability, predictability and change.
• Global Energy and Water EXchanges (GEWEX): GEWEX was previously known as
the Global Energy and Water cycle Experiment but has recently been renamed although
with the same acronym. It focuses on the atmospheric, terrestrial, radiative,
hydrological and coupled processes and interactions that determine the global and
regional hydrological cycle, radiation and energy transitions and their involvement in
global changes such as increases in greenhouse gases.
• Stratospheric Processes And their Role in Climate (SPARC): SPARC has as its
principal focus research on the significant role played by stratospheric processes in the
Earth's climate, with a particular emphasis on the interaction between chemistry and
climate.
There are also several working groups or councils on modeling and data that coordinate
climate observations, modeling and prediction activities across the entire WCRP. The
coordination of research among the physical, biogeochemical, socio-economic dimension
of global change research has been achieved through Earth System Science Partnership
(ESSP) which is being succeeded by a new initiative entitled ''Future Earth: research for
global sustainability'' http://www.icsu.org/future-earth .
The Joint Scientific Committee of the WCRP is considering several scientific Grand
Challenges that emerged from the consultation with the global scientific community at a
recent WCRP Open Science Conference to be the major foci for the WCRP activities
during the next decade (Asrar et al. 2012b ). They include:
• Provision of skillful future climate information on regional scales
• Regional Sea-Level Rise
• Cryosphere response to climate change
• Improved understanding of the interactions of clouds, aerosols, precipitation, and
radiation and their contributions to climate sensitivity
• Past and future changes in water availability
• Science underpinning the prediction and attribution of extreme events.
Although global water cycle is affected by and affects all of these, we focus only on the
last two challenges that involve water and the hydrological cycle for this monograph.
3 The Global Water Budget and Hydrological Cycle
As the climate changes partly from human activities, the water cycle is also changing
(Trenberth 2011 ). Moreover, demand for water continues to increase owing to growing
population, enhanced agricultural and industrial development, and other human activities
such as transformation of landscape and construction of dams and reservoirs, so that very
little of the land surface remains in a natural state. This affects the disposition of water
when it hits the ground: how much runs off, and how much finds its way to rivers or
infiltrates into the soil and percolates to depths to replenish the underground water
reservoirs.
The adverse impact of such activities is not confined to quantity and distribution of
water, but also increasingly affects water quality. Water is used in various ways: such as
through irrigation or by consumption in other human activities; reservoirs and artificial
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