The Portuguese climate is classified as Mediterranean, with some variations depending on orography and latitude. The annual cycles of monthly mean
precipitation and temperature (minimum and maximum) reveal that warm and dry summers are more pronounced in the southern regions. This type of climate presents several drawbacks to agriculture, the major one being insufficient rainfall during the summer or spring seasons (Pinto and Brandao, 2002). Most of the rainfall occurs during winter season, from November until March. The majority of soils in Portugal are badly drained and suffer from water logging during the rainy season. A significant decrease in spring precipitation has been observed for last two decades.
There is a lag between the rainy season and the growing season. The critical period for water requirement by crops is in the spring. The lack of the coincidence between radiation and heat on the one hand, and soil water availability on the other, limits the agricultural productivity and crop yields in drier regions that do not have irrigation facilities (Pinto and Brandao, 2002). If in some years the cold season is dry, it leads to water stress and damages dry land crops, mainly wheat, rye, oats, and barley.
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