Data, Models and Uncertainties in the Global Water Cycle

Abstract

Growing water scarcity will be a major challenge for society in the 21st century. Tackling this challenge requires a multi-scale and interdisciplinary approach to water science in order to understand the complex and interlinked nature of the global water system and how it may change now and in future. There are still considerable uncertainties in our quantification and understanding of the global water cycle. One of the major themes for Global Energy and Water Exchanges (GEWEX, a core project of the World Climate Research Programme) in the coming years is to better understand and predict precipitation variability and changes, and to understand how changes in land surface and hydrology influence past and future changes in water resources and security. These questions focus on the exploitation of improved data sets of precipitation, soil moisture, evapotranspiration, and related variables to close the water budget over land, for providing improved information for products related to water quantity and quality for decision makers, and for initializing seasonal and long-term climate change projections. Through a number of case studies this paper explores newly available data sets and modelling initiatives describing the global water cycle and its associated uncertainties. These studies illustrate how the GEWEX science questions cover many of the challenges facing water science in the coming years, including the improvement of our modelling and prediction of precipitation and evaporation, the development and use of new data sets, the better understanding of extremes and the representation of realistic land surface complexity, with all anthropogenic influences, into our analysis. The ultimate result should be better and more relevant tools to inform society of potential impacts and adaptation options to climate and environmental change.