Demand and Supply of Water for Agriculture: Influence of Topography and Climate in Pre-Alpine, Mesoscale Catchments

Jürg Fuhrer,Karsten Jasper

doi:10.4236/nr.2012.33019

Abstract

With climate change, water may become limited for intensive agriculture even in regions presently considered “water-rich”. Information about the potential water requirement and its temporal and spatial variability can help to develop future water management plans. A case study was carried out for Switzerland with its highly complex pre-alpine topography and steep gradients in climate. The hydrological model WaSiM-ETH was used to simulate net irrigation requirement (NIR) for cropland, grassland and orchards using criteria to define irrigation periods based either on the water stress level (expressed by the ratio of actual (aET) to potential evapotranspiration ((pET) (Method 1) or on thresholds for soil water potential (Method 2). Simulations for selected catchments were carried out with a daily time step for the period 1981-2010 using a 500 × 500 m spatial resolution. Catchment-scale NIR ranged between 0 and 4.3 million m3 and 0 and 7.3 million m3 for the two methods, respectively, with no trend over the observation period in any catchment. During the heat wave in 2003, NIR increased by a factor of 1.5 to 2.3 relative to the mean, and in catchments where discharge is directly dependent on precipitation, NIR in the summer of 2003 reached the limits of river water availability. In contrast, in a region with water supply from glacier melt water, highest NIR in 2003 still remained far below total river discharge. The results show that NIR varies strongly between years and across the landscape, and even in a presently cool-temperate climate, irrigation may put pressure on regional water resources under extreme climatic conditions that may become more frequent by the end of the 21st century.

Highlights

Agriculture is among the sectors most directly affected by climate variability and climate change, which is mainly due to the strong dependency of crop and livestock production on water, and to the tight link to the global hydrological cycle [1]
The results show that Net irrigation requirement (NIR) varies strongly between years and across the landscape, and even in a presently cool-temperate climate, irrigation may put pressure on regional water resources under extreme climatic conditions that may become more frequent by the end of the 21st century
Water limitation is central to the discussion of possible effects of climate change on agricultural production [1], and measures to improve agricultural water management to cope with increasing drought risks and water scarcity is a common element in national adaptation strategies [34]

Summary

Introduction

Agriculture is among the sectors most directly affected by climate variability and climate change, which is mainly due to the strong dependency of crop and livestock production on water, and to the tight link to the global hydrological cycle [1]. In many rain-fed production systems water is limiting agricultural output because the climatic water balance, i.e. the ratio between precipitation (P) and potential evapotranspiration (pET), is low [2]. In most Central and Northern European regions supplemental irrigation is only used to optimize yields of selected high-value crops during episodes of high pET P ratios, and agricultural water use is currently of minor importance [4]. Outputs of global and regional climate models project a further increase and a spread of dry spells across Europe during this century [8]. Water-related problems in agricultural production could become more serious in the long-run, even in today’s cool and humid regions [9]

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Conclusion