## 4 Discussion
Examples of commonly used hydrologic models include HEC-HMS, SWMM (stormwater management model), and TR-20 [52; 53; 54]. These models consider the presence of green infrastructure, detention/retention facilities, or other stormwater management practices that affect the runoff characteristics. Since the values of rainfall intensities are defined by zone or calculated with information that is generally not available in developing countries, the use of simple methods with many assumptions is common. As an example, the delineation of urban basin boundaries is traditionally carried out with automatic digital tools. These tools are based on the use of DEMs with poor resolution and do not properly consider the effect of urbanization [55], which can distort the understanding of the surface rainfall flow pattern in the study area. In addition, the presence of the subsurface storm drainage system can greatly modify this flow pattern. The proposed methodology is simple and has advantages over other more sophisticated methodologies that require detailed basic information [6; 20; 21; 56]. This information on various occasions is limited or nonexistent, especially in terms of data corresponding to the topography of the surface of urban areas where the natural terrain conditions have been modified [9]. Obtaining accurate data, such as rainfall data, soil properties, land use, and topographic information, can be challenging and time-consuming in developed countries [25]. In our methodology, this problem is solved by generating a high-resolution digital surface model using photogrammetry, which is a cost-effective and less time-consuming option than traditional methodologies that require ground-level topographic surveys. This allows for accurate and rapid basin mapping, which facilitates the study of surface water flow on a basin basis rather than by urban development zone. Then, this methodology does include a procedure to delineate the basins under study. In this same sense, our methodology involves using a procedure to estimate rainfall intensity whose parameters are adjusted based on local information, which has yielded appropriate results in Mexico. The rational method is proposed because it continues to be an international standard due to its simplicity and wide use. It requires the determination of the runoff coefficient, which is based on land use and type. Land use can be determined based on the photographsobtained as a partial product of the UAV flights of this methodology. However, the determination of soil type will depend on previous studies in the study area. We recognize that the methodology proposed here has some disadvantages. One, perhaps the main one, which is also common to other methodologies, is the lack of model calibration. This is because it does not include field corroboration by means of a measurement network of the design flow rates. In addition, the design flow rate corresponds to the flow rate of the basin as a whole; however, our study shows that it is not only discharged through a single point of interest (in this case, the location of the sewer) but also through other points of water parting. These correspond to streets that mainly constitute the surface drainage network of the area under study. Therefore, the flow rate flowing through the sewer is lower than that calculated with the rational method. Our case study does not include the transfer of flows from the basin under study to other basins through the secondary or subway storm drainage network, except for the flow through the pipe connected to a sewer. This did not allow the influence of such transfers to be included in the methodology.