Maximum precipitation over 5 consecutive days
Maximum daily precipitation over 5 days is an indicator of the highest volume of water (in the form of rain, snow, sleet or hail) recorded over the course of 5 consecutive days, measured in millimetres (mm) or its equivalent litres per square metre (l/m²). This indicator describes the trends for maximum precipitation over 5 days in the Basque Country between 1971 and 2016 and plays an important role when applied to agriculture and water resource management, as well as in preventing persistent precipitation events.
- Between 1971 and 2016, the trend for maximum precipitation over 5 consecutive days in the Basque Country as a whole is not significant.
- The decadal rates of change for maximum precipitation over 5 consecutive days at a spatial level are not uniform and show only a few small areas with a significant increase or decrease in maximum precipitation over 5 consecutive days dotted over the entire region.
Relationship of the indicator to climate change
Changes in precipitation are one of the most important impacts of climate change. Precipitation is intermittent and, when it occurs, its nature depends largely on meteorological conditions, which determine the supply of moisture through winds and evaporation on the surface. One consequence of global warming is increased evaporation. Increased evaporation is likely to lead to more precipitation on a global scale. However, this increase in evaporation and precipitation may not be evenly distributed. Similarly, global warming accelerates evaporation from the ground surface and increases the potential incidence and severity of droughts.
Run-off from accumulated precipitation may impair the quality of water as pollutants deposited on land reach water bodies. In turn, droughts can affect the amount of water available for drinking, irrigation and industry. Therefore, it is necessary to analyse how changes in precipitation may affect accumulated precipitation in the Basque Country.
Figure 1. Time series for the maximum precipitation over 5 consecutive days in the period 1971-2016 for the Basque Country as a whole (correlation coefficient R = 0.026, p-value = 0.81.
In this section, we will analyse the evolution of maximum precipitation over 5 consecutive days in the Basque Country between 1971 and 2016.
Figure 1 shows the time series for maximum precipitation over 5 consecutive days for the Basque Country as a whole. A slight positive trend was observed for the period of data analysed, but as this was not significant (p=0.81), no conclusions can be drawn.
Figure 2. Rate of change of maximum precipitation over 5 consecutive days in the Basque Country (mm per decade), 1971-2016.
Figure 2 represents the decadal rate of change for maximum precipitation over 5 consecutive days at a spatial level. The highest rate of significant change is observed in the eastern parts of the territory, albeit anecdotally. The most important aspect is that the decadal changes in the maximum precipitation over 5 consecutive days in most of the Basque Country are neither uniform nor significant.
Precipitation measurements in the Basque Country come from meteorological stations, both manual and automatic, managed by different institutions (Basque Government, Provincial Councils, AEMET, URA).
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 point for the calculation of this climate change 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”
These maps are used to calculate the maximum precipitation over 5 consecutive days for each year, defined as the highest precipitation recorded over 5 consecutive days.
We can also calculate the decadal trend (Sen's slope), i.e. the increase/decrease in the magnitude of maximum precipitation over 5 days over a decade, and check whether the trend is statistically significant or whether it is really the result of the variability of the thermometric series itself (Mann Kendall test).
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