Climate Change in Portugal


Observations

Meteorological observations are used fo preparation of weather analysis, forecasts and severe weather warnings, for the study of climate, for hydrology and agrometeorology, and for research in meteorology and climatology. To compare results between different regions, it became necessary to define criteria of international standards related to the spatio-temporal resolution of meteorological phenomena. The World Meteorological Organization defined an interval of 30 years as a standard for the calculation of climatological normals. A 30 years' period is long enough to assess the mean and variability of relevant quantities such as temperature, precipitation or wind. The climate normal period is calculated from 1971 to 2000.

Processing of climatological normals is carried out on a series of observational data. Normal values ​​depend on the available observations from each weather station, and can be grouped into two groups:

  • average monthly values ​​of  variables observed (minimum, mean and maximum temperature and precipitation amount).
  • average number of days  of observed metereological conditions (eg. strong wind, heavy rainfall, etc.).

The source of climate information is Portugal Climate Atlas (available from IPMA). Climatological parameters of air temperature and precipitation, observed in 61 climatological stations (eg. IM) and 260 pluviometric stations (eg. INAG), was obtained from the interpolation of mean values ​​ 1971-2000 period. Average values ​​of minimum, maximum and mean air temperature and total precipitation were produced through a multivariate regression with altitude and distance from the coast and ordinary spatial interpolation of residuals by kriging. Normal kriging was used for interpolation of the number of days with minimum, maximum temperature and precipitation. Manual modeling of experimental variogram was aided and optimized using the analysis of various types of error obtained by cross validation.