Maximum average air temperature
Maximum average air temperature measures heat in the atmosphere in degrees Celsius (°C). This indicator describes the trends in maximum 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 maximum air temperature.
- Since 1971 there has been an upward trend in the maximum average air temperature in the Basque Country, with an increase of 0.28 °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.
- Spring is by far the season of the year with the highest increase, followed by summer and autumn to a lesser extent, which are all statistically significant. Winter shows no statistical sign of change 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. Thus, extreme heat can lead to premature death from heat stroke and contribute to the exacerbate cardiovascular diseases, especially in high-risk groups such as people over the age of 65, a growing demographic group. On the other hand, abnormally high maximum 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 maximum 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. Maximum average air temperature anomaly (°C) in the Basque Country, 1971-2016.
Figure 1 shows the annual anomalies compared to the maximum average temperature for the standard period 1971 - 2000. For example, an anomaly of +1 degree means that the maximum 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 maximum average air temperature (°C per decade) in the Basque Country, 1971-2016.
The spatial variability in surface 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 maximum 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 can see spring is by far the season with the highest increase, followed by summer, and to a lesser extent, autumn, all statistically significant. Winter shows no statistical sign of change 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 series the maximum temperature refers to the highest temperature value in a day, which under normal conditions and without taking into account other meteorological factors, is reached in the early afternoon.
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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The Basque Country
+0.28 ºC
Per decade since 1971