Projecting North Eastern Italy temperature and precipitation secular records onto a high-resolution grid M. Brunetti a , G. Lentini b , M. Maugeri b , T. Nanni a, * , C. Simolo a , J. Spinoni a a Istituto di Scienze dell’Atmosfera e del Clima (ISAC-CNR), via Gobetti 101, I-40129 Bologna, Italy b Universitá degli Studi di Milano, Dipartimento di Fisica, via Celoria 16, I-20133 Milano, Italy article info Article history: Received 30 March 2009 Received in revised form 4 September 2009 Accepted 21 December 2009 Available online 4 January 2010 Keywords: Climatology High-resolution grid Precipitation Temperature Climate reconstruction abstract Thirty-arc-second resolution monthly temperature and precipitation climatologies for North Eastern Italy are presented and the procedure we adopted in order to superimpose the information of the secular anomaly records to these climatologies is discussed. Temperature climatologies are obtained by means of a step-wise linear regression method which aims at determining the temperature dependence on geo- graphical and morphological variables. In the first regression (temperature versus elevation) the recorded data are considered; the further regressions concern the residuals obtained after taking into account the effect of each variable, in order of importance. Precipitation climatologies are obtained by means of a pro- cedure which consists in considering each cell of a high-resolution grid and in using the 15 closest sta- tions in order to perform a weighted local linear regression of precipitation versus elevation: the weights are given by the distances of the stations from the grid point and by the level of similarity between the stations cells and the considered grid cell in terms of elevation, slope steepness, slope ori- entation and distance from the sea. Secular records to be superimposed to the climatologies can be obtained for each grid point by means of a distance-weighted average of the anomaly temperature and precipitation records of the neighbouring stations. Ó 2009 Elsevier Ltd. All rights reserved. 1. Introduction Spatial climate data sets in digital form are currently in great demand and gridded estimates of monthly temperature and pre- cipitation 30-years climatological normals are requested by a vari- ety of models and decision support tools, such as those used in agriculture, engineering, hydrology, ecology and natural resource conservation (Daly et al., 2002; Daly, 2006). These data sets have to be set up providing a realistic representation of the major forc- ing factors that affect spatial climate patterns, in order to give rea- sonable estimates also for areas with poor station coverage such as high elevation sites in mountain areas (Daly et al., 2008). Beside the spatial distribution of the climatological normals, it is also important to describe the spatio-temporal behaviour of climate variability and change. Such information turns out to be funda- mental within climate impact-related researches which may con- cern local scales such as, e.g., a winter resort or an experimental crop field. It is therefore necessary to set up methodologies allowing to estimate both the temperature and precipitation climatological normals of any point of the territory and the corresponding long- term records. As the desired resolution turns often out to be rather high (e.g., 1 km 2 ), such spatialisation methodologies present a number of non trivial issues. In this context this paper discusses two different methodologies: one for the estimation of monthly secular temperature records and one for the precipitation ones, for any point of a high-resolution grid covering North Eastern Italy (44.5–47N, 10–14E). The study area (Fig. 1) covers the basin of the Adige River and the whole Italian territory to the North and to the East of this basin. The first assumption of our research is the anomaly method (New et al., 2000; Mitchell and Jones, 2005). This method assumes that the spatio-temporal structure of the signal of a meteorological variable over a given area can be described by the superimposition of two fields: the climatological normals over a given reference period (i.e. the climatologies) and the departures from them (i.e. the anomalies). The former are basically linked to the geographical features of the territory and they can manifest remarkable spatial gradients. On the contrary, the latter are linked to climate variabil- ity and change and they are generally characterized by higher spa- tial coherence. On this assumption the two fields can be reconstructed in a completely independent way from each other and they can be based on different data sets. Such data sets have obviously to be constructed by the selection of the records fulfilling completely different criteria: for the anomalies the priority lies in data quality and in the availability of long records (in our case we aim at covering at least the last 130 years); for the climatologies 1474-7065/$ - see front matter Ó 2009 Elsevier Ltd. All rights reserved. doi:10.1016/j.pce.2009.12.005 * Corresponding author. E-mail address: t.nanni@isac.cnr.it (T. Nanni). Physics and Chemistry of the Earth 40-41 (2012) 9–22 Contents lists available at ScienceDirect Physics and Chemistry of the Earth journal homepage: www.elsevier.com/locate/pce