Spatio-temporal land-use changes in the Colima-Villa de Álvarez metropolitan area, and their relationship to floodings
During last decade, Colima town suffered from an increase in flooding and inundation. These episodes occurred during extreme rainfall events, such as hurricanes Jova in2011and Manuelin2013 both with averages rainfall intensities of 200 mm per day, but also during high intensity and short duration rainfall through the rain season.
Natural soils in the region are derived from the volcaniclastic deposits originated from the activity of the Volcán de Colima. Land use analyses were performed based on field work on a target area(TA) that was then used to perform a supervised classification using SPOT images taken in 2005, 2009 and 2015 in the studied area that corresponds with the hydrological basin that drains into the urban area of Colima and Villa de Ávarez. The three main land use classifications were defined: Native, Cultivated and Urban surfaces (each of them with their own subdivisions). 33 soil samples were collected and analyzed to determine their physical proprieties such as: particle size distribution, bulk and particle densities, water weight and soil porosity, organic matter content, pH and electrical conductivity. The in situ hydraulic conductivity test was done using a Drip-Infiltrometer device to obtain the Ks value.
Soils correspond to Andosols with more than 88% sand, up to 8% silt and 3% clay. They came out positive in the allophane test in more than 80% of the samples. The average water contents were of 14%, 21% and 13% for natural, cultivated and urban soils respectively. Bulk density average values were below 1.30 gr/cm3 and particle average densities below 2.30 gr/cm3. Porosity varies from 29 to 55%. The organic matter vary from almost cero to 11%. pH data pointed to the existence of phosphorus, iron, copper, zinc, and manganese and the electric conductivity classified them as sodic soils. in the in situ infiltration experiments yielded Ks values of 32.16 to 0.50 mm/h for native soils, Ks of 25 mm/h for cultivated and Ks from 10 to 0.8 mm/h for urban soils.
Land use time-space analysis in the TA showed that from 2005 to 2015 the urban land use growth was of 13%,cultivated lands decreased an 11%, while natural areas decreased only 1%.For the complete study zone, urban land use increased by2% from 2005 to 2009 and remained in the same amount for 2015. From2009 to 2015 cultivated area decreases by8%and change to native lands due to field abandoning.Based on this research results, the increase in flooding and inundation in the Colima-Villa de Álvarez area could be related to the land use change, especially the increase in urban land that largely reduce the infiltration rate as the decrease in cultivated area which resulted to be the type of soil in the area with the highest infiltration rate. These anthropic land use evolution promotes inundation not only during extreme hydrometeorological event but also during the common rainfalls events causing several damages on infrastructures and death.