The climate in mainland Portugal is predominantly influenced by latitude, orography and its proximity to the Atlantic Ocean. Climate variables, such as precipitation and temperature, display strong north-south and west-east gradients as well as a very sharp seasonal and inter-annual variability. Average annual precipitation in mainland Portugal shows a strong spatial variability, with the highest values observed in the mountainous regions of Minho, exceeding 2,500 mm, and the lowest values, below 600 mm, in some northern and central inland regions (non-mountainous areas) and in inland Alentejo. On average, around 40% of annual precipitation occurs during winter (December to February) and only 7% of total annual precipitation occurs during summer (June to August). Transition seasons – spring (March to May) and autumn (September to November) – show a very variable inter-annual distribution, with approximately 24% and 28% of total average precipitation during these seasons, respectively. Average annual temperature is between 6°C and 9°C in inland North and Centre and higher, above 17°C in eastern Algarve and the Guadiana valley.
- Since the mid-70s, the average temperature has risen in all regions of Portugal at a rate of approximately 0.3°C/decade. Out of the ten warmest years, seven occurred after 1990, with 1997 being the warmest year.
- An increase in the number of days with high temperatures and a decrease in the number of days with low temperatures has been observed. There has also been an observed increase in the intensity and duration of heat waves.
- Annual precipitation has decreased (-25 mm/decade): the last 20 years have had particularly low rainfall in mainland Portugal. Five out of the ten driest years occurred after 2000, with 2005 being the driest year, 2007 the second driest, and 2004 the third driest.
- The last four decades have been continuously drier, the driest one being 2001 – 2010. There has been an increase in extremely rainy days (above the 99th percentile) within annual precipitation, especially in the past 30 years and in southern regions (1971 – 2015).