Quantifying and Reducing Uncertainty in the Large-Scale Response of the Water Cycle - The Earth's Hydrological Cycle - page 66

Quantifying and Reducing Uncertainty
in the Large-Scale Response of the Water Cycle

Gill M. Martin

Received: 31 May 2012 / Accepted: 4 September 2012 / Published online: 5 October 2012
Her Majesty the Queen in Right of United Kingdom 2012

Abstract Despite their obvious environmental, societal and economic importance, our
understanding of the causes and magnitude of the variations in the global water cycle is
still unsatisfactory. Uncertainties in hydrological predictions from the current generation of
models pose a serious challenge to the reliability of forecasts and projections across time
and space scales. This paper provides an overview of the current issues and challenges in
modelling various aspects of the Earth's hydrological cycle. These include: the global
water budget and water conservation, the role of model resolution and parametrisation of
precipitation-generating processes on the representation of the global and regional
hydrological cycle, representation of clouds and microphysical processes, rainfall vari-
ability, the influence of land-atmosphere coupling on rainfall patterns and their variability,
monsoon processes and teleconnections, and ocean and cryosphere modelling. We con-
clude that continued collaborative activity in the areas of model development across
timescales, process studies and climate change studies will provide better understanding of
how and why the hydrological cycle may change, and better estimation of uncertainty in
model projections of changes in the global water cycle.

Keywords Hydrological cycle Moisture Precipitation Modelling

1 Introduction

The hydrological cycle is the process by which water travels from the Earth's surface to the
atmosphere and then back to the surface again. The sun provides the energy for a continuous
exchange of moisture between the oceans, the land and the atmosphere. The atmospheric
water cycle is the driving force of weather and climate, and the spatial and temporal char-
acteristics of precipitation—too much, too little, at the wrong time, in the wrong place—have
profound effects on all aspects of life. Substantial changes in the global water cycle (GWC)
are an expected consequence of a warming climate. Such changes could prove a significant