STREAMFLOW RESPONSE TO LAND-COVER CHANGE IN SOUTHERN MEXICO: PROJECTIONS OF WATER BALANCE IN THE TULIJÁ RIVER WATERSHED

Abstract

  Vegetation plays a crucial part in the water distribution within watersheds, as the type and extension of land cover influences the interaction of complex spatio-temporal hydrologic processes. Hydrologic simulations have been previously used to quantify the hydrologic response of a watershed to different land cover scenarios. In this study the SWAT model has been applied to expand the understanding of the net effect of land cover change in the northern portion of the state of Chiapas in southeastern Mexico. As a first step a statistical analysis was performed for climatologic and streamflow records of the watershed. Then the SWAT model was calibrated and validated for watershed streamflow records. Later the model was applied to changing land-cover under future climate data generated over the next 60 years. The model performance was verified using standard metrics such as Nash-Sutcliffe efficiency coefficient, bR², and percent bias.  The impact of land cover change on the monthly and annual water balance was consistently proven by the model. The decrease of forested land significantly decreased monthly streamflow for dry months, and increased the maximum streamflow during wet months. The results from this study do not account for local climate and geomorphology feedback; however, it highlights the importance of the incorporation of land management practices in local development plans.  

Table of Contents

List of Figures …………………………………………………………………………………………………………………….. v List of Tables ………………………………………………………………………………………………………………………. vi Acknowledgements ……………………………………………………………………………………………………………. vii CHAPTER 1:     Introduction………………………………………………………………………………………………….. 1 CHAPTER 2:    Background …………………………………………………………………………………………………… 3 The Tulijá River Watershed ……………………………………………………………………………………. 4 CHAPTER 3:     Methods ………………………………………………………………………………………………………. 6 Statistical Analysis of Time Series …………………………………………………………………………… 6 Hydrologic Modeling …………………………………………………………………………………………….. 8 Adaptation to perennial vegetation in the tropics ……………………………………………… 9 Parameterization, Calibration, and Validation …………………………………………………. 11 Land-Cover Change …………………………………………………………………………………………….. 12 MarkSim model ………………………………………………………………………………………………….. 14 Analyzing the Impact …………………………………………………………………………………………… 14 CHAPTER 4:    Datasets ……………………………………………………………………………………………………… 15 CHAPTER 5:     Results and Discussion …………………………………………………………………………………. 19 Statistical Analysis ………………………………………………………………………………………………. 19 Hydrologic Modeling …………………………………………………………………………………………… 24 Land-Cover Change …………………………………………………………………………………………….. 27 Water balance changes between 1970s and 2016 …………………………………………… 27 Modeling Future Streamflow ………………………………………………………………………… 30 CHAPTER 6:     Conclusions…………………………………………………………………………………………………. 34 Apendix:  SWAT Input Data ………………………………………………………………………………………………… 36 Bibliography …………………………………………………………………………………………………………………….. 38

CHAPTER 1:  Introduction

  Of the challenges facing the Earth over the next century, land-use and land-cover change are likely to be the most significant (Mustard et al. 2004). It has been recognized that land-use change has multiple and substantial effects on key parameters that affect biogeophysical processes of the hydrologic cycle, including evapotranspiration, precipitation, surface runoff, streamflow, infiltration, groundwater recharge, and heat fluxes  (Feddema et al. 2005; DeFries & Eshleman 2004; Matheussen et al. 2000). It is a major issue, to the point that some suggest that the consequences may outweigh those from climate change (Sala 2000). To date, research investigating the consequences of land-use has focused on three main issues: (1) the effects of land-use change on climate (Sagan et al. 1979), (2) the effects of habitat loss on biodiversity (Sala 2000), and (3) the linkage between vegetative cover and hydrologic processes (DeFries & Eshleman 2004). Although, isolating the impacts of land-cover change on water resources is challenging (Stonestrom et al. 2009) due to the complex interaction of processes at different scales. The southeastern region of Mexico is notable because of its high biodiversity and environmental heterogeneity (Echeverria et al. 2006); however, forest degradation has been occurring in this area for centuries as a result of traditional slash-and-burn agricultural activities (Lee 1994). Moreover, population has grown in a way that has led to intensification of agriculture through the expansion of areas for cultivation at the expense of forested lands (Ochoa-Gaona & González-Espinosa 2000). The current main cause of human driven degradation and deforestation in the southern state of Chiapas is due to land-cover change for agricultural and livestock production (Gonzalez-Espinosa et al. 2009; PACCC 2012). In this context, the objective of the current project is to contribute to the understanding of the net hydrological effect of land-cover change through deforestation, fragmentation, and degradation of the tropical forest of the Tulijá River basin in northern Chiapas, Mexico. In particular the study aims at: (1) providing an initial statistical analysis of hydroclimatic time series used throughout the study;  (2) calibrating and validating the SWAT model with streamflow records for the period 1968-1978; and (3) projecting to the year 2075 the possible effects of progressive forest removal in the watershed. STREAMFLOW RESPONSE TO LAND-COVER CHANGE IN SOUTHERN MEXICO: PROJECTIONS OF WATER BALANCE IN THE TULIJÁ RIVER WATERSHED