Minimum Average air temperature
The minimum average air temperature measures heat in the atmosphere in degrees Celsius (°C). This indicator describes the trends in minimum average air temperature in the Basque Country from 1971 to 2016 and shows how much it has contributed to the upward trend observed in the minimum air temperature.
- Since 1971 there has been an upward trend in the minimum average air temperature in the Basque Country, with an increase of 0.39 °C per decade.
- The rates of change at spatial level are increasing, evenly distributed over a large part of the territory and are statistically significant.
- This increasing behaviour is similar in all seasons of the year, except in winter, with no significant trend over the period.
Relationship of the indicator to climate change
Air temperature is a basic indicator in climate description. It affects ecosystems, including human, in a crucial way. Mortality rates in winter months are higher than in non-winter months, partly due to cold temperatures which can exacerbate pre-existing medical conditions such as cardiovascular and respiratory diseases. More directly, people exposed to extreme cold conditions may also suffer frostbite and hypothermia. Nevertheless, abnormally high minimum temperatures can alter a wide range of natural processes, especially if these changes occur too rapidly for plant and animal species to be able to adapt.
Trends over time and indication of climate change
This section describes in detail the average rate of evolution of the minimum average air temperature in the Basque Country since 1971. We identified jumps in the series and the warmest and coldest years on record.
Figure 1. Minimum average air temperature anomaly (°C) in the Basque Country, 1971-2016.
Figure 1 shows the annual anomalies compared to the minimum average temperature for the standard period 1971 - 2000. For example, an anomaly of +1 degree means that the minimum average temperature was 1 degree higher than the average for the standard period.
The 70s was the coldest decade of the standard period considered, with 1972 being the coldest year. Significant positive anomalies are identified from 1989 onwards. After a clear slowdown in the first decade of the 2000s, the second decade saw a rapid rise again.
Figure 2. Rate of change of minimum average air temperature (°C per decade) in the Basque Country, 1971-2016.
The spatial variability in air temperature in the Basque Country since 1971 are evenly distributed over a large part of the territory and are statistically significant. However, there are some areas with a negative trend, probably due to problems in the characterisation of the altitude gradient in the spatial estimation process.
Figure 3. Evolution of the annual minimum average air temperature by season in the Basque Country, 1971-2016.
It is also worth considering whether this warm trend is uniform depending on the time of year. Analysing Figure 3, we see this increasing behaviour is similar in all seasons of the year, except in winter, with no significant trend over the period.
Air temperature in the Basque Country is measured in both manual and automatic weather stations managed by different institutions (Basque Government, Provincial Councils, Central Government).
In daily resolution data sets the minimum temperature refers to the lowest temperature value in a day, which is often recorded just after sunrise, when the Sun becomes visible over the horizon.
Data series have been fed into spatial prediction models to generate a daily resolution cartographic database, which is the starting point for the calculation of this climate change indicator. Static covariates, derived from digital terrain models, have been included in this prediction to explain air temperature.
The cartographic database comes from Phase II of the KLIMATEK project - "High Resolution Climate Change Scenarios for the Basque Country" (http://escenariosklima.ihobe.eus/data)
Based on these maps, monthly anomalies are calculated, in relation to the standard period 1971-2000, and then averaged to find an annual temperature anomaly for each year. These regional anomalies are then averaged for the territory as a whole.
Decadal trends (Sen’s slope), i.e. magnitude of mean temperature increases/decreases over a decade, is also calculated; and it is checked whether the trend is statistically significant or whether it is actually the result of the variability of the thermometric series itself using the Mann Kendall (MK) test.
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Proyecto Klimatek 2016. Elaboración de escenarios regionales de cambio climático de alta resolución sobre en Euskadi. IHOBE. Gobierno Vasco.
The Basque Country
+0.39 ºC
Per decade since 1971