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The image above shows the surface interpolation results. The portion of the image on the left shows the location and color-coded rainfall totals for the various rain gauges in Arizona for a six month period in 1983. The portion of the image on the right shows the interpolated results.
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These four images were generated by taking the individual monthly image results and computing a sum using the three winter rain months (January, February, and March) and the three summer/monsoon rain months (July, August, and September). The resulting images represent six month rainfall totals for 1983 (upper left/wet year), 1982 (upper right/ normal year), 1981 (lower left/moderately dry year), and 1980 (lower right/normal year). The colors represent a total rainfall range from 3 to 28 inches for the six month period shown.
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The digital image data can be used to compare differences in both the temporal and spatial distribution of rainfall. One method of doing this is by generating difference/change images between the various temporal image products. The two images shown above are color-coded difference images generated using the 1982/normal year differenced with the 1983/wet year (left) and then differenced with the 1981/moderately dry year (right). These image products show both where, and how much, the wet and moderately dry years differed from the normal year rainfall. The scale at the bottom associates the difference amounts in inches and the background color, representing a difference of zero, can be used as a guide as to where the rainfall was more or less than the normal year. Notice that even during a wet year there are areas that are dryer than the normal year, as well as in a dry year there are areas that are wetter than the normal year. This shows that care must be taken when working with ground-based instrument readings because regional wet-/dry-year ratings may not necessarily mean that those conditions exist at the instrumented ground site, or vice versa.
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Once the monthly rainfall images are generated, they can be analyzed and compared in any desired combination (e.g., in six month sums shown above). However, they can also be used on an individual monthly basis over a selected period of time to visually and statistically study and compare temporal and spatial relationships and changes in rainfall. As an example, the 48 months of rainfall data were all color coded to the same range (0 to 6 inches) and displayed in the short temporal movie shown above. This type of visualization can help in the analysis and comparison of temporal and spatial patterns and variations.