Landscape hydrology of rural areas: Challenges and tools

Abstract

Currently the world hosts seven billion people that require food. About one third of the earth’s land area is now intensively used by agriculture, and another third extensively. Agriculture inevitably depends on soil quality as well as on water resources. More than 70% of human water use is due to irrigation. In addition, transpiration from rainfed agriculture comprises a substantial part of the earth’s water cycle. Thus, land use both highly depends and affects water availability and is intimately intertwined with water resources management. The term ‘‘landscape’’ is used here to account for a variety of feedback effects between natural resources, human land use, economy and demography. The world population continues to increase. In addition, growth of economic wealth in many countries increased demand for upmarket agricultural products, and there is increasing demand for biofuel production as well which increases pressure on soil and water at a global scale. During the last 50 years cultivated area per capita decreased by half and likely will continue to decrease. Thus there is urgent need for advanced concepts of sustainable use of water and soil resources. Already today groundwater and river water over-exploitation due to increasing irrigation is a matter of concern. In some regions groundwater levels have been decreasing by 1 m per year during the last decades. Even large rivers fell increasingly dry. This has severe implications for water resources further downstream, not to mention biodiversity aspects. For example, the Aral Sea has been shrinking by more than 90% within a few decades, giving place to a hostile salt desert. Thus, inefficient water management and land degradation are closely connected to each other. Climate change is now considered an increasing threat on water resources. Increasing air temperature is often associated with increasing evapotranspiration and thus increasing utilization of rare water resources. However, this is an oversimplification. On the one hand, warmer air masses can transport more water vapour, and increasing temperature comes along with increasing energy for mass transport which could even increase precipitation. In addition, higher CO2 partial pressure likely will increase water use efficiency of plants and thus reduce water consumption. On the other hand, large scale atmospheric circulation patterns most probably will be affected by climate change and thus change spatial patterns of precipitation which is not trivial to predict. Correspondingly, climate change models are fraught with large uncertainties with respect to precipitation. However, experts agree that in general frequency and intensity of extreme events like floods and drought likely will increase which poses agricultural management and soil resources at increasing risk. Besides, melting of glaciers in mountainous regions currently increases water availability in the lowlands downstream, whereas the opposite is true in the long-term. Thus there is urgent need for an ‘‘Integrated Water Resources Management’’ (IWRM) which has to include soil quality management as well. Various ideas, concepts and methods exist. However, local conditions have to be considered. Thus, experience from different parts of the world needs to be exchanged. This book is intended to contribute to that.