A moving windows visual approach to analysing spatial variation in temperature trends on the Spanish mainland 1951–2010

In this article, we approached the study of spatiotemporal variation in trends for the monthly mean values of maximum and minimum temperatures on the Spanish mainland between 1951 and 2010, in order to find out how length and selected periods affected trends. The trend and significance signals were calculated every month and for each cell individually, in a high spatial resolution grid (Mann–Kendall test) by using decreasing and increasing temporal windows (from 20 to 60 years and vice versa). Finally, the results are presented as a sequence of temporal window trend maps to show the spatiotemporal variability of trends at high resolution over the years. The results of increasing temporal window trends show that temperatures have increased overall on the Spanish mainland, but the impact is different for cold and warm months, maximum and minimum temperatures, and the area affected by significant trends varies depending on the month. The positive and significant trend affecting >20% of the total area extends in a west–east gradient during the cold months, while the reverse is true for the warmest ones. The analyses from decreasing the length of moving windows also vary greatly among months. The areas affected by significant trends are highly variable month-on-month, differ for maximum and minimum temperatures, and evolve in different ways over time. Few months show a significant trend during the last 30 years, and spatial distribution differences among trends for the maximum and minimum temperatures are detected. Spatially, a more complex gradient can be observed, but the global east–west and west–east gradient can also be generally seen in the warmest or coldest months. These findings show that a selected period determines the final trend. Furthermore, the results suggest that recent warming processes on the Spanish mainland have high spatial variability that differs among months and maximum and minimum temperatures, and has not been constant.