Changes in Intense Precipitation Events in Mexico City

Abstract

he authors analyzed an extensive precipitation dataset available for the Mexico City basin that included hourly precipitation in various sectors of the city from 1993 to 2007. Observations indicated that significant changes occurred in the timing and number of intense events (precipitation rate >20 mm h?1) over this time period. Alternative hypotheses that changes in the emission of aerosol pollutants or in the land use can result in the observed variations are tested. The Weather Research and Forecasting Model was used to simulate September precipitation from 2002 to 2011 at the peak of the wet season. Changes were introduced to the microphysical scheme as a proxy for differences in the aerosol population and the droplet activation spectra. Simulations were also performed with the land use of the urban areas set up to represent older and more current conditions. Results indicate that increased pollution (decreased urban area) led to an average precipitation decrease over the mountain areas of 20%?40% (10%?20%) and an increase of 20% (30%) to the east of Mexico City. The timing of intense precipitation shifts from 1900 to 1600 LT for the polluted and decreased urban area cases when compared to a control experiment. These results add valuable information about how precipitation is modified by complex terrain and surface exchange processes in large urban areas under wet conditions.