Data

The dataset is part of the effort to provide the most detailed climate data for CAPLTER and related projects. This dataset represents average monthly rainfall derived from spatial interpolation of daily rainfall data from a dense network of precipitation sensors for the period of 5 years (2000-2005).

Meteorological data acquisition and preprocessing

Precipitation data were obtained from different sources including the Flood Control Disctrict of Maricopa County (ALERT), the National Weather Service (NWS), the Arizona Meteorological Network (AZMET), and the Phoenix Real-time Instrumentation for Surface Meteorological Studies (PRISMS) Network. Instrument locations were first geocoded using the station descriptions from each network. Daily measurements were then aggregated to bi-weekly periods to match the temporal resolution of MODIS (The Moderate Resolution Imaging Spectroradiometer) Normalized Difference Vegetation Index (NDVI) images. MODIS is a key instrument aboard the Terra (EOS AM) and Aqua (EOS PM) satellites designed for global monitoring of key biophysical parameters including vegetation. Tables with aggregated precipitation were then joined to the shapefile of precipitaiton sensors.

Spatial interpolation

I performed ordinary kriging to create precipitaion surfaces. The maps were created using Geostatistical Analyst, the ArcGIS 9.1 extension. Spherical models were used in all semivariogram models and predictions were checked interactively using the built-in tools. Standard Error maps were also produced along with prediction surfaces that were all rasterized to a 250 meter resolution grid.

Temporal aggregations

Biweekly precipitation surfaces were aggregated to monthly time step. In turn monthly surfaces were summed up to derive annual precipitation grids. For each month I computed the average 6-year precipitaion. Finally the average annual precipitation was also computed for the period of 2000-2006.