Number of heat waves
The number of heat waves is an indicator of the heat in the atmosphere. This indicator describes heat wave trends in the Basque Country between 1971 and 2016. This is an important index when applied to fields such as agriculture, tourism or human health.
- Since 1971, there has been an upward trend in the number of heat waves in the Basque Country, with an increase of 0.14 days per decade.
- The spatial variability in the number of heat waves is not uniform across the region. It affects the Mediterranean region and Gipuzkoa to a higher extent, and Bizkaia to a lesser degree.
Relationship of the indicator to climate change
A heat wave or extreme heat event is an abnormally hot period of several days. As a result of climate change, the duration, frequency and intensity of heat waves will increase in the future. This increase will lead to a substantial increase in the mortality rate in the coming decades, unless adaptation measures are taken.
Heat waves are associated with a decrease in the general well-being of the population and an increase in mortality and morbidity, particularly in vulnerable population groups. Older people are more vulnerable to the effects of heat waves, due in part to poorer physical health and the effects of cognitive impairment on the perception of the health risks related to heat. People with chronic illnesses and those of a lower socio-economic standing also have a higher risk of heat-related death. Moreover, the health risks during periods of extreme heat are higher for those who are physically very active. This is of importance as far as outdoor recreational activities are concerned, and is particularly relevant to the impacts of climate change on occupational health.
Figure 1. Time series of the number of heat waves in the period 1971-2016 for the Basque Country as a whole.
A time series analysis of the number of heat waves shows a significant positive trend (p = 0.00065) at a rate of 0.14 events per decade for the period 1971-2016 (Figure 1).
Figure 2. Rate of change in the number of heat waves (no. of events) in the Basque Country, 1971-2016.
The spatial variability in the number of heat waves in the Basque Country is not uniform across the region (Figure 2). A more pronounced and statistically significant trend can be observed in the Mediterranean region and in Gipuzkoa. Interestingly, the extent to which Bizkaia would be affected would be lower in. The highest rates of change would be throughout the Baias and Oria basins, with between 1-2 more events per decade.
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.
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”.
These maps are used to calculate the number of heat waves (events) per year, i.e. the individual number of heat waves that occur in the warm period (May - September), defined as 3 or more days where the daily maximum temperature 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
+0.14 days
Per decade since 1971