Crete is the largest of the Greek islands, and the 5th largest in the Mediterranean, with a total area of 8,265 km2. While retaining its own local cultural traits, the island shapes a significant part of the cultural heritage of Greece, but also contributes 5% of the national Gross Domestic Product (GDP), with agriculture and tourism as its main industries.
|Spatial distribution of soil erosion on the Island of Crete.|
Crete’s climate is classified as dry sub-humid (Csa according to Köppen and Geiger, Mediterranean South). About 53% of the annual precipitation occurs in the winter, 23% during autumn, 20% during spring while there is negligible rainfall during summer (Koutroulis and Tsanis, 2010). Annual rainfall ranges from 300 to 700 mm from east to west in the low areas along the coast, and from 700 to 1000 mm in the plains of the mainland, while in the mountainous areas it reaches up to 2000 mm. The annual water balance breaks down to 68-76% evapotranspiration, 14-17% infiltration and 10-15% runoff. Soils are mainly Calcisol.
Almost 40% of the island is cultivated at various intensities depending on desired end product quality and intended market: e.g. olive trees can be non-irrigated (traditional/household use) or irrigated (modern/intense), vineyards may be conventional or organic, etc.
Types of crop
Agriculture is an important source of income, contributing to Crete’s GDP by 13%. Olive is the most important crop, cultivated on all soils and terrain slopes up to altitudes of about 900 m. Specifically for Chania, agricultural land is divided in 5 main crop categories: grapes 3%, trees 90% (olive trees 70%, other trees 20%), vegetables 2%, and other crops 5%.
Management of soil, water, nutrients and pests
Irrigation types on the island vary depending on crops and local water availability (e.g. olive trees are either regularly irrigated or not irrigated at all, orange groves are often waterlogged and vineyards are often drip irrigated). Fertilisation also varies (chemicals vs animal manure). Due to high ownership fragmentation and rough topography, management is seldom large scale, and crop picking is almost always traditional and labour intensive using minimal mechanical equipment.
Soil improving cropping system and techniques currently used
Several technologies, mainly associated with cropping intensity and traditional versus moderns techniques, are currently practices in the island. For example, olive trees are cultivated with little or no irrigation and minimum agricultural inputs, minimised tillage and minimised removal of rocks from the fields. Also, vineyards focused on producing quality winemaking grapes practice green manuring, green strips and minimised tillage with lightweight machinery.
Problems that cause yield loss or increased costs
Crete represents Mediterranean soils under imminent threat of desertification, characterized by loss of vegetation, water erosion, and subsequently loss of soil. Several large scale studies have estimated average soil erosion in the island between 6 and 8 t ha-1 y-1 but more localised investigations assess soil losses one order of magnitude higher (Panagos et al., 2014). Olive orchards and vineyards often suffer from extreme soil erosion by water due to farm slope and recent intensification of till practices. Depending on practices, tilling and irrigation can increase soil erosion, but the potential net yield of a non-irrigated olive field can drop by about 30%. Nevertheless, irrigated trees are less resilient to water stress due to shallow root depth. The long-term impact of soil erosion on farm yield due to the loss of soil profile can be detrimental. During the project, soil erosion estimates will be validated and innovative techniques will be assessed for their potential to improve soil quality and mitigate erosion.
External drivers or factors
Institutional and political drivers
By joining the European Economic Community in 1981, Greek agriculture became subject to the Common Agricultural Policy (CAP). Until 1992, the aim of the CAP was to increase production, and to provide cheap rural products accompanied by reasonable rural incomes. Accordingly, agricultural production was intensified and mechanized, unique endogenous varieties were replaced by hybrids aimed for the needs of globalized markets, and the adoption of monocultures led to some extent to the loss of self-sufficiency. In addition, regional development, infrastructure, spatial planning policies and the implementation of Integrated Mediterranean Programmes constitute the factors that have considerably affected the exploitation of natural resources (Daliakopoulos and Tsanis, 2014).
The rapid development of Crete in the last 30 years has exerted strong pressures on many financial sectors in the region. Urbanization and growth of agriculture, tourism and industry had strong impact on the water resources of the island by substantially increasing water demand. Total water uses in the region in 2000 amounted to 420 million m3, approximately 5.5% of the precipitation of a normal year (Fasoulas et al., 2002). Of this, 16% is used for domestic, tourist, and industrial uses, 3% for livestock and a vast 81% for irrigated agriculture on approximately 30% of the total cultivated land, using mainly ground water in drip irrigation methods. Irrigation and tourism create peak demands resulting in a marked seasonal pattern in water demand with an annual volume of water abstracted exceeding 50% of the average annual runoff and 35% of the groundwater potential. Regarding future water demands, recent estimates (Koutroulis et al., 2015) forecast total uses for the year 2015 in the order of 550 m3/y. It is therefore considered essential to encounter the increasingly severe water problems faced in the Island only by strategic policies using integrated water management.
The state of the art on climate change research for the Mediterranean region indicates a strong susceptibility to change in hydrological regimes. During the last decade, the island of Crete has faced an increased number of floods and droughts. While future regional precipitation patterns are uncertain, a mean temperature increase of 3.4oC is projected over the next century in the northern Mediterranean (Daliakopoulos and Tsanis, 2014). This warming trend and the resulting drought episodes will potentially force Crete to exceed ecological thresholds of water and vegetation stress that can be potentially mitigated with the use of more resilient and sustainable agricultural practices. Also, the analysis of climate models data indicates that today’s extreme events will intensify, i.e., precipitation on average is likely to be less frequent but more intense and droughts are likely to become more frequent and severe in some regions (Koutroulis et al., 2015), thus leading to greater erosion events.