Statistics for Spatial Data.

Cause, conseguenze e strategie di mitigazione Proponiamo il primo di una serie di articoli in cui affronteremo l’attuale problema dei mutamenti climatici. Presentiamo il documento redatto, votato e pubblicato dall’Ipcc - Comitato intergovernativo sui cambiamenti climatici - che illustra la sintesi delle ricerche svolte su questo tema rilevante.

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Climate Change 2007: The Physical Science Basis.

On robust estimation of the location parameter

The Climate Hazards group Infrared Precipitation with Stations (CHIRPS) dataset builds on previous approaches to ‘smart’ interpolation techniques and high resolution, long period of record precipitation estimates based on infrared Cold Cloud Duration (CCD) observations. The algorithm i) is built around a 0.05° climatology that incorporates satellite information to represent sparsely gauged locations, ii) incorporates daily, pentadal, and monthly 1981-present 0.05° CCD-based precipitation estimates, iii) blends station data to produce a preliminary information product with a latency of about 2 days and a final product with an average latency of about 3 weeks, and iv) uses a novel blending procedure incorporating the spatial correlation structure of CCD-estimates to assign interpolation weights. We present the CHIRPS algorithm, global and regional validation results, and show how CHIRPS can be used to quantify the hydrologic impacts of decreasing precipitation and rising air temperatures in the Greater Horn of Africa. Using the Variable Infiltration Capacity model, we show that CHIRPS can support effective hydrologic forecasts and trend analyses in southeastern Ethiopia.

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The climate hazards infrared precipitation with stations--a new environmental record for monitoring extremes.

We present a European land-only daily high-resolution gridded data set for precipitation and minimum, maximum, and mean surface temperature for the period 1950-2006. This data set improves on previous products in its spatial resolution and extent, time period, number of contributing stations, and attention to finding the most appropriate method for spatial interpolation of daily climate observations. The gridded data are delivered on four spatial resolutions to match the grids used in previous products as well as many of the rotated pole Regional Climate Models (RCMs) currently in use. Each data set has been designed to provide the best estimate of grid box averages rather than point values to enable direct comparison with RCMs. We employ a three-step process of interpolation, by first interpolating the monthly precipitation totals and monthly mean temperature using three-dimensional thin-plate splines, then interpolating the daily anomalies using indicator and universal kriging for precipitation and kriging with an external drift for temperature, then combining the monthly and daily estimates. Interpolation uncertainty is quantified by the provision of daily standard errors for every grid square. The daily uncertainty averaged across the entire region is shown to be largely dependent on the season and number of contributing observations. We examine the effect that interpolation has on the magnitude of the extremes in the observations by calculating areal reduction factors for daily maximum temperature and precipitation events with return periods up to 10 years. Copyright 2008 by the American Geophysical Union.

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A European daily high-resolution gridded data set of surface temperature and precipitation for 1950-2006

Optimal areal rainfall estimation using raingauges and satellite data

The Fourier Integral Method (FIM) of spectral simulation, adapted to generate realizations of a random function in one, two, or three dimensions, is shown to be an efficient technique of non-conditional geostatistical simulation. The main contribution is the use of the fast Fourier transform for both numerical calculus of the density spectral function and as generator of random finite multidimensional sequences with imposed covariance. Results obtained with the FIM are compared with those obtained by other classic methods: Shinozuka and Jan Method in 1D and Turning Bands Method in 2D and 3D, the points for and against different methodologies are discussed. Moreover, with the FIM the simulation of nested structures, one of which can be a nugget effect and the simulation of both zonal and geometric anisotropy is straightforward. All steps taken to implement the FIM methodology are discussed.

The Fourier Integral Method: An efficient spectral method for simulation of random fields

Optimal selection of number and location of rainfall gauges for areal rainfall estimation using geostatistics and simulated annealing

Downscaling cokriging for image sharpening

The results of estimating the areal average climatological rainfall mean in the Guadalhorce river basin in southern Spain are presented in this paper. The classical Thiessen method and three different geostatistical approaches (ordinary kriging, cokriging and kriging with an external drift) have been used as estimators and their results are compared and discussed. The first two methods use only rainfall information, while cokriging and kriging with an external drift use both precipitation data and orographic information (easily accessible from topographic maps). In the case study presented, kriging with an external drift seems to give the most coherent results in accordance with cross-validation statistics. If there is a correlation between climatological rainfall mean and altitude, it seems logical that the inclusion of topographic information should improve the estimates. Kriging with an external drift has the advantage of requiring a less demanding variogram analysis than cokriging. © 1998 Royal Meteorological Society.

http://mmc2.geofisica.unam.mx/cursos/geoest/Articulos/Geostatistics/Comparison%20of%20geostatistical%20methods%20for%20estimating%20the%20areal%20average%20climatological%20rainfall%20mean%20using%20data%20on%20precipitation%20and%20topography.pdf

Eulogio Pardo-Igúzquiza

Papers

Optimal areal rainfall estimation using raingauges and satellite data

The Fourier Integral Method: An efficient spectral method for simulation of random fields

Optimal selection of number and location of rainfall gauges for areal rainfall estimation using geostatistics and simulated annealing

Downscaling cokriging for image sharpening

Comparison of geostatistical methods for estimating the areal average climatological rainfall mean using data on precipitation and topography