Geoscience Reference
In-Depth Information
intensification and industrialization are changing hydrological systems in complex ways,
and on many of the world's major rivers, water management is changing flows, often with
severe effects on downstream users, aquatic ecosystems and freshwater discharges to the
world's seas and oceans. Superposed on these pressures, expected climate change and
climate variability can combine to create extreme and perhaps unprecedented conditions
which have high impact consequences for human populations, economic assets and critical
physical infrastructure. This unique combination of pressures has exposed weaknesses in
current water governance and management. It has increased the awareness of uncertainties,
the complexity of the systems to be managed, and the need for profound changes in policy
and management paradigms, as well as governance systems.
The World Climate Research Programme (WCRP) has a unique role to play in
developing the new scientific understanding and modeling and prediction tools needed for
a new era of global water management. WCRP mainly through GEWEX, and based on
significant contributions from CLIVAR and CliC projects, is well poised to motivate a new
generation of land surface and global hydrological models, building on recent develop-
ments in Earth observations, that represent the dynamics of major managed water systems.
The modeling activities have an equally important role in motivating a new generation of
weather-resolving climate models that are capable of simulating and potentially predicting
the basic modes of variability, whether arising from sea surface temperature and ocean,
land surface moisture, sea ice or other sources that are known to drive global precipitation
variability and extremes on seasonal to decadal time scales. Such prediction systems are
increasingly necessary to address regional impacts of climate change.
The vast majority of water comes from precipitation—either directly or indirectly
through runoff from distant locations. From a climate perspective, it is therefore an
imperative to understand the natural variability of precipitation in the system, as well as its
susceptibility to change from external forcings. Within GEWEX, the Global Precipitation
Climatology Project (GPCP) (Huffman et al.
2009
) has been a focus of improving esti-
mates of precipitation. Because of its inherently intermittent nature, it is a major challenge
to determine precipitation amounts reliably with a few instantaneous observations of rates
such as from available satellites. Improved observations and analysis products related to
precipitation and the entire hydrological cycle and their use in evaluating and improving
weather, climate and hydrological models are important and tractable over the next 5 to
10 years.
The specific questions that will be addressed over the next 5-10 years include:
•
How well can precipitation be described by various observing systems, and what basic
measurement deficiencies and model assumptions determine the uncertainty estimates at
various space and time scales? Despite the significant improvements in many observing
systems during the past two decades, the uncertainty in precipitation estimates lies not
only in the measurement error itself, but in the space/time interpolation of a naturally
discontinuous and intermittent field and/or in the assumptions needed to convert a
physical measurement from remote sensing into a precipitation amount. Critical water
source regions often reside in complex terrain where sampling issues, remote sensing
artifacts and limitations are compounded. The errors are not static but instead depend on
the nature of the precipitation itself. Focusing on the large-scale environment
responsible for the precipitation therefore holds hope to build not only better rainfall
products, but characterizing the uncertainties in a verifiable manner as well. Regional
hydroclimate projects provide detailed understanding that translate the large-scale
information into usable information for decision makers.
