Mapping minimum daily temperature in Spain using kriging with external drift

Abstract

The spatial interpolation of daily temperature is often a complex process compared to the interpolation of monthly or annual data due to the necessity of dealing with local phenomenons, such as inversions, that frequently affect the daily temperatures, especially in mountainous regions. The objective of this study is to describe the methodology that it is being used in the Spanish Meteorological Agency for obtaining gridded fields of daily minimum temperature using a universal kriging method with with the altitude and the distance to the coast as an external drift. In this method, the vertical temperature gradient can vary from one point to another in the study region, so that temperature inversion effects can be properly considered in the interpolation process. A validation process is shown, including a comparison with other typical interpolation methods: regression kriging, ordinary kriging and inverse distance weighted. Finally, some examples of maps obtained by this method are shown, including several products generated for agroclimatological purposes by combining daily gridded maps, such as average number of frost days, mean first and last freezing date and average chill hours below different temperature thresholds.