Water is essential to life on Earth, plays a key role in the development and functioning of society, and is a high priority resource for sustainable development. Many aspects of the Earth's water cycle are not well understood or simulated by climate models. One thrust of the Water System effort is to reduce this uncertainty through improved understanding and parameterization of the water cycle in climate models. Another component of the Water System effort is to examine the impact of a changing water system on water management and policy. A complete understanding of the water system requires an approach that extends beyond atmospheric analysis to include ground and surface water cycling and the water resources implications associated with change in an evolving Earth system.
The Water System Program has conducted research related to the Regional and Global water cycle since 2001. Using the diurnal cycle of precipitation as a focus, research has shown that current climate models do not accurately simulate the frequency, intensity, and timing of summer time convection over much of the globe, including continental regions, despite reasonable simulations of precipitation amount (see figure). This model deficiency greatly hampers climate models' ability to predict future changes in intense storms, flash floods, tornados, hurricanes, and other severe weather events that likely have the largest impact on the society under global warming. This model deficiency results from a variety of factors, including:
This later deficiency is reflected in the high degree of uncertainty of current climate model runs in these regions.
An overarching goal is to improve the representation of the water cycle in climate models. While climate models typically predict temperature with reasonable confidence, predictions of precipitation are notably weak. Our focus has been on the diurnal cycle of warm season precipitation including diagnoses of rainfall climatology downwind of major mountain ranges over continental regions. These global and regional studies have shown that such regions are frequented by organized convection, which propagates and may produce up to 70% of the observed warm season precipitation. These systems, however, are inadequately represented in current global and regional climate models. IPCC4 projections of precipitation trends highlight these regions as having the largest variability or uncertainty. This component of the program will focus on two areas during the next 5 years:
While precipitation is a key component of the water cycle, water processes at the land surface and below ground play a similarly important role. The terrestrial hydrologic cycle is driven by water and energy fluxes at scales smaller than the grid spacing of climate system models. Efforts during the next five years will focus on improved representation of hydrologic processes, such as routing and infiltration of water, as part of land models within regional and global climate system models, and the emergent Earth system modeling efforts. This will include water processes at the land surface and below, as well as the important interactions with carbon and nitrogen cycles.
ISP and RAL jointly conduct coordinated Water System research that will span predictions in the physical water cycle, water resources and societal impacts known as Societal, Water, the Atmosphere and Natural Systems (SWANS).
The first project, Colorado Headwaters, focuses on critical questions concerning the effect of climate change on snow processes in the western cordillera of North America. It employs both high resolution models and observations, and addresses the resulting implications for water management and policy. This five–year project is a major focus of the Water System program. More generally, studies of hydrological extremes are a shared priority for ISP and RAL research, including the study of floods and droughts in future climate scenarios and the fate of aquifers under stress from climate change and human exploitation.
The Water System Program has conducted research related to the Regional and Global water cycle since 2001 with university collaboration. Using the diurnal cycle of precipitation as a focus, research has shown that current climate models do not accurately simulate the frequency, intensity, and timing of summer time convection over continental regions. Much of the reason for this error is in the poor simulation of propagating systems of convection in the lee of major mountain ranges by current convective parameterization schemes. This error is reflected in the high degree of uncertainty of current climate model runs in these regions.
The goals of the Water System Convective Parameterization program are:
The latter goal aims at examining whether the often tight coupling between precipitation and soil moisture in climate models is realistic, and its role in modulating and initiating propagating convection.
The Water System Program will continue to focus on improving convective parameterizations in climate models, including the testing of various candidate schemes (including the new Moncreiff and Liu scheme developed under Water System sponsorship) and continuation of the scientific interest group on convective parameterization.
Water Systems Program