Mediterranean irrigation under climate change: more efficient irrigation needed to compensate for increases in irrigation water requirements

M Fader,S Shi,W Von Bloh,W Cramer,A Bondeau

doi:10.5194/hess-20-953-2016

Abstract

Abstract. Irrigation in the Mediterranean is of vital importance for food security, employment and economic development. This study systematically assesses how climate change and increases in atmospheric CO2 concentrations may affect irrigation requirements in the Mediterranean region by 2080–2090. Future demographic change and technological improvements in irrigation systems are taken into account, as is the spread of climate forcing, warming levels and potential realization of the CO2-fertilization effect. Vegetation growth, phenology, agricultural production and irrigation water requirements and withdrawal were simulated with the process-based ecohydrological and agro-ecosystem model LPJmL (Lund–Potsdam–Jena managed Land) after an extensive development that comprised the improved representation of Mediterranean crops. At present the Mediterranean region could save 35 % of water by implementing more efficient irrigation and conveyance systems. Some countries such as Syria, Egypt and Turkey have a higher savings potential than others. Currently some crops, especially sugar cane and agricultural trees, consume on average more irrigation water per hectare than annual crops. Different crops show different magnitudes of changes in net irrigation requirements due to climate change, the increases being most pronounced in agricultural trees. The Mediterranean area as a whole may face an increase in gross irrigation requirements between 4 and 18 % from climate change alone if irrigation systems and conveyance are not improved (4 and 18 % with 2 °C global warming combined with the full CO2-fertilization effect and 5 °C global warming combined with no CO2-fertilization effect, respectively). Population growth increases these numbers to 22 and 74 %, respectively, affecting mainly the southern and eastern Mediterranean. However, improved irrigation technologies and conveyance systems have a large water saving potential, especially in the eastern Mediterranean, and may be able to compensate to some degree for the increases due to climate change and population growth. Both subregions would need around 35 % more water than today if they implement some degree of modernization of irrigation and conveyance systems and benefit from the CO2-fertilization effect. Nevertheless, water scarcity may pose further challenges to the agricultural sector: Algeria, Libya, Israel, Jordan, Lebanon, Syria, Serbia, Morocco, Tunisia and Spain have a high risk of not being able to sustainably meet future irrigation water requirements in some scenarios. The results presented in this study point to the necessity of performing further research on climate-friendly agro-ecosystems in order to assess, on the one hand, their degree of resilience to climate shocks and, on the other hand, their adaptation potential when confronted with higher temperatures and changes in water availability.

Highlights

Water is a scarce resource in the Mediterranean region, in absolute terms and through the concentration of precipitation in the winter months and the high interannual variability with the presence of frequent droughts (Lionello et al, 2006)
The present study aims to advance substantially the present research status by taking into account, in a comprehensive framework, several previously unconsidered variables: climate change impacts on irrigation water requirements in the Mediterranean region are simulated with a newly developed version of the LPJmL model that considers 88 % of irrigated areas and represents the special structure of Mediterranean agriculture, which is dominated by perennial crops (Fader et al, 2015)
Annual crops grow and are harvested according to the heat unit theory and agricultural trees are implemented as evergreen or summer green trees, where the fruits are represented by a plant-specific portion of net primary productivity (NPP)

Summary

Introduction

Water is a scarce resource in the Mediterranean region, in absolute terms and through the concentration of precipitation in the winter months and the high interannual variability with the presence of frequent droughts (Lionello et al, 2006). For example Vautard et al (2014) calculated precipitation decreases reaching 20 % for 2 ◦C global warming and state that southern Europe is likely to experience higher warming than the global average, especially in summer. Climate change is not the only factor affecting water supply and demand; population and economic growth in the countries of the southern Mediterranean and urbanization in the entire Mediterranean region will very likely further increase water extractions. The urban population in northern Africa and southern Europe is expected to increase from 51 to 63 % and from 70 to 80 %, respectively (United Nations, 2014), leading to more water consumption, higher water demand for energy production and changes in hygiene behaviour. The expansion of tourism is expected to increase water demand, especially in the dry period (Lanquar, 2013)

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