| Floods and droughts are the
two important aspects of hydrological hazard. Floods usually result
either from heavy precipitation (rain or snow) or from rapid snowmelt
or glacier discharge (CliC).
Droughts are caused by dry weather conditions in which evaporation
exceeds the available surface water. They are frequently characterised
by water shortages. Understanding the causes and forecasting of heavy
or scant precipitation and high evaporative demand (and hence of floods
and droughts) form an important objective of the WCRP. The WCRP research
examines these two types of extreme hydrological events in a variety
of ways.
The WCRP project,
Global Energy
and Water Cycle Experiment (GEWEX), is the main area that researches
the planet’s hydrological cycle in all its aspects including
its variability and change. GEWEX focuses on land and its role in
causing floods and droughts. Another WCRP project, Climate
Variability and Predictability (CLIVAR), facilitates research
into floods and droughts resulting from impacts of atmospheric and
oceanic variability. The modelling and prediction of excess or lack
of precipitation is an important objective of the WCRP/CAS (Commission
on Atmospheric Sciences) Working
Group on Numerical Experimentation (WGNE). The natural variability
of floods and droughts and their change are studied by the WCRP
Working Group on Coupled Modelling
(WGCM) and the CLIVAR Working
Group on Seasonal to Interannual Prediction (WGSIP). While these
activities study physical aspects of floods and droughts, the Global
Water System Project (GWSP) of the Earth
System Science Partnership (ESSP) focusses on how humans are
changing the global water cycle, thus impacting floods and droughts.
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