El Niño 1997–98 and the hydrometeorological variability of Chapala, a shallow tropical lake in Mexico

One hundred years chronological water level fluctuations for Chapala Lake, a shallow tropical lake in west Mexico, as well as their relationships with air temperature fluctuations, precipitation and Lerma River discharge are examined in this study. It is shown, that these relationships were strongly revealed in the last 1997–98 El Niño, which caused anomalous air temperature and evaporation increase throughout Western Mexico territory and, as a consequence, 1 m downturn of the Chapala lake level since January till June, 1998. To investigate 1997–1998 El Niño-Southern Oscillation phenomenon (ENSO 1997–98) AVHRR-NOAA satellite image analysis of the Chapala Lake surface water temperature (LCST) was performed. These images provide a temperature database for 1996–99 (38 months). Analysis of annual and seasonal LCST fluctuations was carried out using monthly averages for this period. Time series analysis on the LCST data suggest that seasonal surface temperature variations may be almost completely obscured by the annual harmonic. In 1998 the temperature pattern was altered due to the El Niño 1997–98 episode. In winter the water surface temperature was on average almost 1 °C lower than the temperature values registered in 1996. However, for the summer and autumn of 1998, such temperatures were 1.5 °? higher in comparison with the reference year of 1996.