Modelling hydrological processes in arid and semi-arid areas: an introduction

Abstract

INTRODUCTION In the arid and semi-arid regions of the world, water resources are limited, and under severe and increasing pressure due to expanding populations, increasing per capita water use and irrigation. Point and diffuse pollution, increasing volumes of industrial and domestic waste, and over-abstraction of groundwater provide a major threat to those scarce resources. Floods are infrequent, but extremely damaging, and the threat from floods to lives and infrastructure is increasing, due to urban development. Ecosystems are fragile, and under threat from groundwater abstractions and the management of surface flows. Added to these pressures is the uncertain threat of climate change. Clearly, effective water management is essential, and this requires appropriate decision support systems, including modelling tools. Modelling methods have been widely used for over 40 years for a variety of purposes, but almost all modelling tools have been primarily developed for humid area applications. Arid and semi-arid areas have particular challenges that have received little attention. One of the primary aims of this workshop is to bring together world-wide experience and some of the world's leading experts to provide state-of-the-art guidance for modellers of arid and semi-arid systems. The development of models has gone hand-in-hand with developments in computing power. While event-based models originated in the 1930s and could be used with hand calculation, the first hydrological models for continuous simulation of rainfall-runoff processes emerged in the 1960s, when computing power was sufficient to represent all of the land-phase processes in a simplified, “conceptual” way.