Total Precipitation
Total precipitation is an indicator of the volume of water that the territory receives, in the form of rainfall, snow, sleet or hail (but not in the form of condensation such as fog or dew), which is measured in millimetres (mm) or litres per square metre (l/m2) equivalent. This indicator describes the trends of total precipitation in the Basque Country from 1971 to 2016 and its application is important for agriculture and water resource management.
- Since 1971 a downward trend in total precipitation in the Basque Country can be identified, with a decrease of 13.8 mm/decade, but with a low level of statistical significance (p=0.32).
- A certain spatial pattern can be observed: on the Cantabrian slope there would be a slight negative trend, while the opposite would be the case on the Mediterranean slope.
- Spring and summer are the seasons of the year with the greatest decrease in total precipitation.
Relationship of the indicator to climate change
An analysis of the impact of climate change requires research on changes in precipitation. Precipitation is the general term for rainfall, snowfall and other forms of liquid or frozen water falling from clouds. Precipitation can have wide-ranging effects on human well-being and ecosystems. Precipitation can affect the amount of surface and groundwater available for drinking, irrigation and industry. Changes in precipitations 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.
Due to climate change, changes in the amount of precipitation have been observed. As the average temperature on the Earth's surface rises, evaporation increases, which in turn increases overall precipitation. Therefore, warmer weather is expected to increase precipitation in many areas. However, as precipitation patterns change, so do the effects of climate change on precipitation. As wind patterns and ocean currents that drive the climate system change due to climate change, this also causes some areas to experience a decrease in precipitation. Therefore, analysing the changes in total precipitation in the Basque Country is necessary.
Trends over time and indication of climate change
This section describes in detail the average rate of evolution of the total annual precipitation in the Basque Country since 1971. Jumps in the series and the driest and wettest years on record are identified.
Figure 1. Total precipitation anomaly (mm) in the Basque Country, 1971-2016.
Figure 1 shows annual anomalies compared to the mean precipitation for the standard period 1971 - 2000. For example, an anomaly of +100 mm means that precipitation was 100 mm higher than the average for the standard period.
The 70s was the wettest decade of the standard period considered, with 1979 being the wettest year, followed by 2013. From 1985 onwards, significant negative anomalies were observed, with 1989 being the year of the great drought that occurred between August 1988 and November 1990, in which the metropolitan area of Bilbao and the city of Vitoria-Gasteiz suffered restrictions that affected more than 1,200,000 inhabitants and a major part of the industrial sector.
Figure 2. Rate of change of total precipitation (% mm/decade) in the Basque Country, 1971-2016.
At the spatial level, the rates of change of total precipitation in the Basque Country from 1971 to 2016 show a decrease of 13.8 mm per decade, but with a low level of statistical significance (p=0.32), which could be due to the variability of the rainfall series. However, a certain spatial pattern can be observed, with a negative trend on the Cantabrian slope, while the opposite is true for the Mediterranean.
Figure 3. Evolution of total annual precipitation by season in the Basque Country, 1971-2016.
Regarding the trend according to the time of year, Figure 3 shows that the negative trend is more pronounced in spring and summer, although with low statistical significance.
Precipitation measurements in the Basque Country come from meteorological stations, both manual and automatic, managed by different institutions (Basque Government, Provincial Councils, Central Government).
Precipitation is determined at the manual stations, using the rainfall day, counted from 8:00 AM GMT to 8:00 AM GMT, instead of the calendar day, from 00:00 AM GMT to 12:00 PM GMT, which is normally used. In automatic stations, the accumulation of 144 ten-minute records of the calendar day is considered.
Data series have been fed into spatial prediction models to generate a daily resolution cartographic database, which is the starting source for the calculation of this indicator. Static covariates, derived from digital terrain models, have been included in this prediction to explain precipitation.
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 a precipitation anomaly for each year. These regional anomalies are then averaged for the territory as a whole.
Decadal trends (Sen’s slope), i.e. what magnitude of total annual precipitation increases/decreases over a decade is also calculated (as a percentage); and it is checked whether the trend is statistically significant or whether it is actually the result of the variability of the rainfall 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.
Proyecto Klimatek 2016. Elaboración de escenarios regionales de cambio climático de alta resolución sobre Euskadi. IHOBE. Gobierno Vasco.
Euskadi
-13.8mm
Per decade since 1971