Abstract:The methods for measuring vegetation cover in Mexican forest surveys are subjective and imprecise. The objectives of this research were to compare the sampling designs used to measure the vegetation cover and estimate the over and understory cover in different land uses, using digital photography. The study was carried out in 754 circular sampling sites in central Mexico. Four spatial sampling designs were evaluated in three spatial distribution patterns of the trees. The sampling designs with photographic captures in diagonal form had lower values of mean absolute error (MAE < 0.12) and less variation in random and grouped patterns. The Carbon and Biomass Sampling Plot (CBSP) design was chosen due to its smaller error in the different spatial tree patterns. The image processing was performed using threshold segmentation techniques and was automated through an application developed in the Python language. The two proposed methods to estimate vegetation cover through digital photographs were robust and replicable in all sampling plots with different land uses and different illumination conditions. The automation of the process avoided human estimation errors and ensured the reproducibility of the results. This method is working for regional surveys and could be used in national surveys due to its functionality.

The objective of this research was to determine the relationship between the inefficiency of furrow irrigation, the geometric characteristics of agricultural plots and the depletion of the aquifer conditions of the Laguna Bustillos basin (Chihuahua, Mexico) in recent decades (1991-2012). The main results were: a) the analysis of geometric characteristics showed that the Mennonite properties have the least favorable conditions for the use of furrow irrigation; b) the index of inefficiency of furrow irrigation demonstrated the existence of agricultural plots that exceed 2.5 to 13 times the maximum allowed 2019, Instituto Mexicano de Tecnología del Agua.

La cuantificación de la biomasa aérea y carbono total es importante en el contexto de los mercados del carbono y la productividad forestal, por lo que es necesario el desarrollo de métodos cuantitativos costo-efectivos que reduzcan la incertidumbre en sus estimaciones. El uso de ecuaciones alométricas entre la biomasa aérea total y volumen del fuste o total y entre el diámetro normal y la altura total es práctica común en la evaluación de recursos forestales, donde se usan modelos específicos y generalizados, con diferentes niveles de incertidumbre. En la literatura se han propuesto diversas metodologías para simplificar el uso de tales relaciones alométricas, sugiriendo algunas con bases correctas, pero sin explorar sus implicaciones y matemáticas asociadas. En este trabajo se presenta un marco teórico general de las relaciones entre constantes y exponentes, así como entre exponentes, de ciertas ecuaciones alométricas, usando bases matemáticas relativamente simples. Seguido del desarrollo del marco teórico, se usa una base de parámetros de relaciones alométricas y un conjunto de bases de datos de mediciones de campo. Con lo anterior se obtiene, como resultado las estimaciones que son comparables a las ecuaciones alométricas clásicas, pero con el uso de solo la relación altura total-diámetro normal. Se exploran las consecuencias de la propuesta teórica y se generan recomendaciones para cambiar el paradigma en los desarrollos alométricos tradicionales para plantas leñosas.

Abstract:One of the challenges faced by subwatershed hydrology is the discovery of patterns associated with climate and landscape variability with the available data. This study has three objectives: (1) to evaluate the annual recession curves; (2) to relate the recession parameter (RP) with physiographic characteristics of 21 Mexican subwatersheds in different climate regions; and (3) to formulate a Baseflow (BF) model based on a top-down approach. The RP was calibrated utilizing the largest magnitude curves. The RP was related to topographical, climate and soil variables. A non-linear model was employed to separate the baseflow which considers RP as a recharge rate. Our results show that RP increases with longitude and decreases with latitude. RP displayed a sustained non-linear behavior determined by precipitation rate and evapotranspiration ( P E ) over years and subwatersheds. The model was fit to a parameter concurrent with invariance and space-time symmetry conditions. The dispersion of our model was associated with the product of ( P E ) by the aquifer's transmissivity. We put forward a generalized baseflow model, which made the discrimination of baseflow from direct flow in subwatersheds possible. The proposed model involves the recharge-storage-discharge relation and could be implemented in basins where there are no suitable ground-based data.

Abstract:The identification of the moment when direct flow ends and baseflow begins is one of the biggest challenges of hydrological cycle modeling. The objectives of this research were: to characterize the recession curves (RC) and to separate the components of the hydrograph in a compact model. The RC were extracted from time series in three subwatersheds in Mexico. An expo-linear model was adapted and fitted to the master recession curves to find the transition point of the hydrograph and separate the baseflow. The model discriminated the RC in two decreasing ratios: one linear associated to the direct flow, and one exponential linked to the baseflow. The transition point between these two flows was obtained analytically by equaling both ratios. The derivation of a model parameter allowed to find the maximum points in the hydrometric time series, which were the criterion to separate the baseflow. The application of this model is recommended in the analysis of RC with different magnitudes from the flexibility and attachment to the fundaments of exhaustion of a reservoir.