Sensitivity of Mexican water bodies to regional climatic change: three study alternatives applied to remote sensed data of Lake Patzcuaro

Historical aerial photography over closed basins enables the observation of lake surfaces at variable water levels and climatic conditions. Thus, the assessment at the landscape level of subtle variations in inundated areas depends on a suitable framework for processing historical imagery, frequently available at different scales and resolutions. The present paper deals with Lake Patzcuaro as a case study and the application of three analytical procedures to remote sensed data of 1974, including two maps commercially available and nine aerial photographs. Computer-based processing of images and further incorporation into GIS led to three different outputs: topographic map (TM-GIS), photomosaic 1 (P-1) and photomosaic 2 (P-2). Aerial photographs assemblages were georeferenced by means of GCP's, 86 located by means of INEGI vectorial polygons (P-1), and 40 determined directly at the field by GPS (P-2). In conclusion, TM-GIS lack of photointerpretation for the lake as an image derived from a topographic map; while P-2 involved an unacceptable RMS. P-1 thus became the best option for the calculation of areas not only because of the lower RMS associated, but the additional photointerpretation of limnological zones exclusive to aerial photographs. As a background picture, P-1 also facilitates the analysis of historical images on a comparative basis.