Range of heat waves
The range of heat waves is an indicator of the heat in the atmosphere. This indicator describes heat wave trends in terms of their range in the Basque Country between 1971 and 2016. This is an important index when applied to fields such as agriculture, tourism or human health.
- Between 1971 and 2016, there was an increasing trend in the range of heat waves (i.e. the absolute maximum temperature in a heat wave situation), with a statistically significant increase of 0.4 °C per decade at a significance level of 0.05 (p=0.039).
- The spatial variability in the range of heat waves was almost zero in most of the region, except around the Baias and Oria basins, where a significant positive trend was observed, with increases of more than 1 °C per decade.
Relationship of the indicator to climate change
Heat waves are periods characterised by several days of very hot temperatures compared to local average temperatures. Heat waves can have an impact on human health, infrastructure, energy demand and natural ecosystems.
Unusually hot days and heat waves are a natural part of the daily variability. However, as the Earth's climate warms, hotter than usual days and nights are becoming more common and heat waves are expected to become more intense. The increase in these extreme heat events may lead to more heat-related illnesses and deaths, especially if individuals and communities do not take measures to adapt. Even small increases in extreme heat can lead to more deaths and illnesses. This means that it is important to analyse the change in the range of heat waves in the Basque Country.
Figure 1. Time series of the absolute maximum temperature in a heat wave situation in the period 1971-2016 for the Basque Country as a whole.
A time series analysis of the absolute maximum temperature for the Basque Country as a whole during heat waves shows a statistically significant positive trend, at a significance level of 0.05, but not at the 0.01 level (p=0.039) at a rate of change of 0.4 °C per decade for the period 1971-2016 (Figure 1).
Figure 2. Rate of change of the absolute maximum temperature (°C per decade) in a heat wave situation in the Basque Country, 1971-2016.
At a spatial level, there has been no overall positive trend in the range of heat waves in the Basque Country since 1971, with almost non-existent rates of change in a large part of the region. However, there were exceptions in certain areas, where a significant positive trend was observed around the Baias and Oria basins, with increases of more than 1 °C per decade (Figure 2).
Air temperature in the Basque Country is measured in both manual and automatic weather stations managed by different institutions (Basque Government, Provincial Councils, AEMET, URA).
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.
Las series de datos se han introducido en modelos de predicción espacial para generar una base de datos cartográfica de resolución diaria, la cual es la fuente de partida para el cálculo de este indicador de cambio climático. En dicha predicción se han incluido covariables estáticas, derivadas de modelos digitales del terreno, explicativas de la temperatura del aire.
The cartographic database comes from Phase II of the KLIMATEK project “High Resolution Climate Change Scenarios for the Basque Country”.
These maps are used to calculate the range of heat waves for each year, expressed in this case as the absolute temperature of all heat waves identified by the ‘number of heat waves’ indicator. These have been defined as those events that occur in the warm period (May - September) where the daily maximum temperature on 3 or more days exceeds the 90th percentile of the maximum temperature calculated from the base period 1971-2000.
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.
Gaztelumendi S., Otxoa de Alda K., R. Hernández, M. Maruri, J.A. Aranda, P. Anitua (2018) “The Basque Country Automatic Weather Station Mesonetwork in perspective”. WMO/CIMO Technical Conference on Meteorological and Environmental Instruments and Methods of Observation (CIMO TECO-2018). 8 - 11 October 2018. Amsterdam, The Netherlands.
Hernández R., M. Maruri, K. Otxoa de Alda, J. Egaña, S. Gaztelumendi. (2012) “Quality Control Procedures at Euskalmet Data Center”. Advances in Science and Research – Topical Library, Volume 8, 2012, pp. 129-134.
Herrera, S., J. M. Gutiérrez, R. Ancell, M. R. Pons, M. D. Frías and J. Fernández. 2012. Development and analysis of a 50-year high-resolution daily gridded precipitation dataset over Spain (Spain02). Int. J. Climatology, 32, 74-85, doi: 10.1002/joc.2256.
Herrera, S., J. Fernández and J. M. Gutiérrez. 2016. Update of the Spain02 Gridded Observational Dataset for Euro-CORDEX evaluation: Assessing the Effect of the Interpolation Methodology. Int. J. Climatology, 36, 900-908, doi: 10.1002/joc.4391.
Klein Tank, A.M.G., Zwiers, F.W., Zhang, X. 2009. Guidelines on analysis of extremes in a changing climate in support of informed decisions for adaptation, climate data and monitoring WCDMP-No 72, WMO-TD No 1500, p 5.
Proyecto Klimatek 2016. Elaboración de escenarios regionales de cambio climático de alta resolución sobre el País Vasco. IHOBE. Gobierno Vasco.
The Basque Country
+0.4ºC
Per decade since 1971