Variation of Evapotranspiration in the Northwest of Mexico and its Effect on the Climate Change

This paper presents the results obtained firstly analyzing climatic databases for a minimum period of 20 years in the Sonora River Basin in order to compute ET time series and, secondly comparing them with actual ET (ETa) values obtained using Landsat images. Cluster analysis was applied to achieve a regionalization for the Sonora River Basin allowing the use of Automatic Weather Stations (AWS) to compute ET. Both surface temperature (Ts) and ETa obtained by remote sensing techniques were compared with the ETc results using conventional equations and Ts field measurements. Results showed that crops demand a huge amount of water during drought periods, which cannot be compensated due to rainfall shortage. Also, results indicated that remote sensing provided an ETa value that effectively represents the actual condition of crops. To conclude, even though the region is subject to frequent droughts, there is evidence that: the severe event in the mid 90s (strongly related to El Nintildeo), the effect on the crop yields in the same period and the absence of a trend for precipitation, temperature and ET series from 1980 to 2002 in the three homogeneous regions, led to consider that climate change is related to the intensity and duration of this drought period in the basin.