Modelling the Hydrological Sensitivity to Land
Use Change in a Tropical Mountainous
Environment
by
Mauricio Edilberto Rincón Romero
April 2001
A thesis submitted to the University of London
for the degree of Doctor of Philosophy
Department of Geography
King’s College London
Abstract
The main subject of this thesis is the production of a sensitivity analysis to land use and land cover change (LUCC) for a tropical montane cloud forest (TMCF) environment on the basis of flux responses in a hydrological model. Human pressure is one of the main causes of LUCC in the TMCF which often results in important consequences on natural resources like reduction of water quality, loss of biodiversity, micro-climatic change or ecosystem degradation (Koning et al., 1998). Deforestation of the tropical cloud forest is an activity of recent decades that is modifying the landscape significantly. The impact of this deforestation, rather than the deforestation itself, is studied here by comparing variation in fluxes of erosion and overland flow derived from different land uses within a mountainous tropical forest catchment. A physically based hydrological model of the Tambito watershed, CaucaColombia and 5 LUCC pattern scenarios are implemented for the study. A 2.5D dynamic surface hydrological model integrated with a Geographic Information System (GIS) working on an hourly time step is designed for the catchment, to assess flux variability in time and space. The hydrological model includes the following submodules: solar radiation and energy balance, evaporation, interception and effective precipitation, infiltration, soil hydrological balance, overland flow, recharge and erosion. Three hydro-meteorological stations installed on experimental plots collect basic model information for parameterisation and validation. Experimental description, methodology, field data, model implementation and analysed results are presented. Each LUCC scenario uses 15 to 22 consecutive GIS iterations, which transform forest to pasture within the catchment. Summaries of annual average hydrological flux variations are used in the sensitivity analysis. Multiple linear correlation was carried out for flux variations and hydrological sensitivity with landscape physical properties of the deforested area by iteration for each scenario, in order to determine the correlation between landscape catchment physical properties and hydrological flux sensitivities. This process also facilitated the identification of the topographic characteristics of the most sensitive areas within the catchment to LUCC. The model and statistical analysis provides a means of assessing the contribution of different landscape units to hydrological change in the face of LUCC. The impact of LUCC is assessed in terms of catchment hydrological changes and the areas within the catchment with more hydrological sensitivity to LUCC are identified.
Table of contents
Chapter I Introduction
1.1 Land use and cover change (LUCC): a global issue 1
1.2 LUCC: global impacts 3
1.3 A review of models for LUCC 5
1.3.1 Methods for identifying the impact of LUCC 7
1.3.2 Strategies for evaluating hydrological fluxes in the
assessment of LUCC impact 8
1.4 LUCC: issues and impacts in tropical montane
environments outside Colombia 9
1.5 LUCC in Colombia: History and impacts in hillside
areas 11
1.5.1 Historical review of LUCC in Colombia 11
1.5.2 The hydrological impacts of LUCC in Colombia 16
1.6 Structure of the thesis 20
Chapter II Literature review of hydrological models
applied to LUCC impacts research
2.1 Structure of this chapter 23
2.2 General concepts of hydrological models 23
2.3 A general classification of hydrological models 24
2.4 Handling spatial variability in hydrological models 26
2.5 A review of hydrological models related to LUCC impact 27
2.6 Hydrological modelling in tropical montane
environments 37
2.6.1 A review of modelling studies of the hydrological
impact of LUCC in Colombia 38
2.7 Research approaches to LUCC impacts 39
2.8 Main objective 40
2.9 Specific aims 40
2.10 Rationale 41
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Chapter III Methodology
3.1 Structure of this chapter 42
3.2 Description of the study area 43
3.3 Experimental strategy 49
3.4 Land use change scenario generation for this thesis 50
3.4.1 Estimating initial vegetation cover for LUCC
Scenarios 51
3.4.2 Scenario descriptions 54
3.5 Field methodology 64
3.5.1 Plot scale 64
3.5.1.1 The hydrological weather stations 67
3.5.1.2 Data collected from the weather stations 70
3.5.2 Catchment scale 71
3.5.2.1 Soil data 71
3.5.2.2 vegetation data 74
3.5.2.2.1 Leaf area index 75
3.5.2.2.2 Vegetation cover 76
3.5.2.2.3 Canopy water storage capacity 76
3.5.3 Other spatial data 78
3.6 Hydrological Modelling methodology 83
3.6.1 Introduction 83
3.6.2 Strategy 83
3.6.3 Consideration for modelling process 87
Climate
3.6.4 Solar Radiation sub-model 90
3.6.4.1 Hourly extraterrestrial solar radiation
Model 91
3.6.4.2 Hourly cloud-cover attenuation model 92
3.6.4.3 Net solar radiation function 98
Hydrology
3.6.5 Evaporation sub-model 100
3.6.6 Canopy storage, interception and throughfall 108
3.6.6.1 The Rutter model 111
3.6.7 Sub-surface water sub-model 115
3.6.7.1 Modelling flow of water in porous media 116
3.6.7.2 Soil water retention and matric potential 117
3.6.7.3 Pedotransfer functions 119
3.6.8 Infiltration sub-model 124
3.6.9 Overland flow sub-model 131
3.6.9.1 Sub-model description 131
3.6.9.2 Surface component of overland flow at the
catchment scale 134
3.6.10 Erosion sub-model 134
vii
3.7 Integrating the sub-models in the 1D and 2,5D model 139
3.7.1 Module sequence 139
3.7.2 Data used in the model 140
3.7.3 Parameters used in the model 145
Chapter IV Model results, sensitivity analysis and
validation
4.1 Structure of this chapter 147
4.2 Model results 148
4.2.1 Model results at the plot scale 148
4.2.2 Model results at the catchment scale 156
4.3 Sensitivity analysis of the hydrological model at the
plot scale (1D model) 160
4.3.1 Sensitivity to parameter A of net radiation 162
4.3.2 Sensitivity to parameter B of net radiation
equation 165
4.3.3 Sensitivity to parameter light extinction K 166
4.3.4 Sensitivity to parameter leaf area index (LAI) 168
4.3.5 Sensitivity to parameter maximum canopy water
storage capacity 170
4.3.6 Sensitivity to parameter vegetation cover 172
4.3.7 Percent of variation due to soil texture 176
4.3.8 Sensitivity to parameter soil porosity 178
4.3.9 Sensitivity to parameter soil depth 180
4.3.10 Sensitivity to parameter erodability factor, K1 183
4.3.11 Sensitivity to parameter m factor of erosion
equation 184
4.3.12 Sensitivity to parameter n factor of erosion
equation 185
4.4 Summary of 1D sensitivity analysis 186
4.5 2.5D model sensitivity analysis 187
4.5.1 Definition of topographic characteristics 188
4.5.2 Sensitivity analysis at the catchment scale 189
4.5.2.1 Sensitivity analysis of overland flow to
LUCC at the catchment scale 192
4.5.2.2 Sensitivity analysis of erosion to
LUCC at the catchment scale 207
4.6 Summary of 2.5D sensitivity analysis 220
4.7 Model validation 222
4.7.1 Organisation of this section 222
4.7.2 Field data set for validation 223
4.7.3 Parameters used in validation 223
4.7.4 Validation of net solar radiation 225
4.7.5 Validation of soil moisture 228
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Chapter V Summary, conclusions and further work
5.1 Summary of key finding in this thesis 232
5.2 Conclusions and their implications 232
5.3 Further research and model development 245
Bibliography 248
Appendix I LUCC scenarios 286
Appendix II Collected data from the pasture plot 294
Appendix III Summary of soil analysis samples 298
Appendix IV Summary of vegetation samples for:
canopy water storage capacity, vegetation
cover, and LAI for grassland 300
Appendix V Tambito daily rainfall data 304
Appendix VI Example of input data file for the model 310
Appendix VII Extraterrestrial solar radiation model 315
Appendix VIII Mean value of cloud cover 326
Appendix IX Hydrological of PCRaster program Code 328
Appendix X Summary of physical variables and model
variables response for all scenario 336
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