Multi-scale monitoring and modelling for the analysis of the hydrologic response of southern Ecuadorian Andean páramos

The present research is focused on an “alpine” Neotropical grassland ecosystem, situated between ca. 3500 and 4500 m a.s.l. –locally known as “páramo”– which covers the Andean mountains. Below the páramo, the study area hosts other types of high-altitude Andean ecosystems, such as: tropical montane cloud forest and grasslands. The study area is located in the south-west highlands of the Paute River basin that drains to the Amazon River. These highlands form part of the western Cordillera in the Ecuadorian Andes with a maximum altitude of 4420 m a.s.l. The study area comprises a mountain range from 2647 to 3882 m a.s.l. Two neighbouring basins have been selected from this region: Portete (24.4 km2) and Cumbe (44.0 km2). In addition, a small headwater catchment located in the highlands of the Rircary River basin, a neighbour catchment to Portete (Jordanita, 2.70 km2), is also part of the research area. The overall objective of the research is to show how a multi-scale monitoring set-up for experimental research catchments can be implemented and used to establish the foundations of a hydrological observatory in the southern Ecuadorian Andean region. In addition, the research presents a thoughtful approach to catchment modelling and the interaction between modelling and experimental hydrology. A detailed characterization of the weather of three high-altitude Andean ecosystems (i.e. páramo, tropical montane cloud forest and grasslands) was carried out. As a result, the air temperature patterns recorded in both ecosystems –forest and páramo– were the same. Therefore, it is possible to conclude that the land cover has no influence over the lapse rate air temperature as compared with the effect of the altitude. The altitudinal range analysed was of ca. 1000 m. In addition, the water balance at catchment scale allowed to conclude that the land cover has no significant effect on the Ea as compared with the amount of rainfall that actually receives each ecosystem (páramo or tropical montane cloud forest). Hydrological modelling with TOPMODEL By comparing the results of the implementation of TOPMODEL (a TOPography based hydrological MODEL) for the páramo catchments, it was found that the effective parameters, which reflect the characteristics of the catchments, increase in magnitude as a function of the size of the catchment (which increased from 0.21 km2 up to 4.39 km2). Reliable predictions of TOPMODEL were confirmed by field measurements but, the implicit assumption used to calculate the topographic index (i.e. the upslope contributing area “” should be constant for any point) is not fully valid. This has to be reviewed in future applications of TOPMODEL for páramo, which is suffering more frequent drought events. In this context, the drought analysis allowed to conclude that at the plot scale, the differences between the recovery of the soils were relatively large. The measured water content in páramo soils showed a quicker recovery compared to the mineral soils located below the páramo. At the catchment scale, though, the differences in the speed of recovery derived from the soil water storage simulated by the Probability Distributed Moisture model and the drought analysis was not as pronounced. Only for the prolonged drought event of 2009-2010 were the differences larger. The difference between the precipitation and the potential evapotranspiration has been shown to have more impact on the regional difference in hydrologic behaviour than the difference between the water storage capacities of the soils. Policy makers and researchers will be able to compare these baseline results with future hydrological and soil monitoring data, to track changes in the páramo ecosystem.Contents Acknowledgements 7 Abstract 11 List of abbreviations and acronyms 31 List of symbols 33 1 Introduction 37 1.1 The páramo ecosystem 38 1.1.1 The páramo soils 38 1.2 Hydrological monitoring of Andean ecosystems 39 1.3 Overall and specific objectives of the study 41 2 Hydrological monitoring in tropical Andean mountainous catchments 47 2.1 Introduction 47 2.2 Materials and methods 47 2.2.1 The study area 47 2.2.2 The multi-scale monitoring set-up 79 2.3 Results 93 2.4 Conclusions 94 3 Hydrological regime and water balance in tropical Andean mountainous catchments 95 3.1 Introduction 95 3.2 Materials and methods 95 3.2.1 Weather data processing 95 3.2.2 The potential evapotranspiration 96 3.2.3 The rainfall analysis 98 3.2.4 The flow-duration curves 99 3.2.5 The water balance at catchment scale 99 3.2.6 The analysis of the rainfall-runoff relationship 100 3.2.7 The water balance at plot scale 101 3.3 Results and discussion 103 3.3.1 The weather in the different ecosystems 103 3.3.2 The potential evapotranspiration 118 3.3.3 The rainfall 121 3.3.4 The flow duration curves 125 3.3.5 The water balance at catchment scale 128 3.3.6 The rainfall-runoff relationships 129 3.3.7 The water balance at plot scale 134 3.4 Conclusions 144 4 TOPMODEL in high Andean Ecosystems 149 4.1 Introduction 149 4.2 Materials and methods 152 4.2.1 Data 153 4.2.2 TOPMODEL 156 4.3 Assessing parameter sensitivity 166 4.3.1 Monte Carlo Simulation 166 4.3.2 Generalized Sensitivity Analysis (GSA) 168 4.3.3 Parameter response surfaces 169 4.4 Model calibration 170 4.5 Model evaluation 170 4.6 Results and discussion 172 4.6.1 Digital terrain analysis 172 4.6.2 Variable and parameter ranges 175 4.6.3 Implementation of TOPMODEL 184 4.6.4 Assessment of the performance of TOPMODEL at small catchment scale in páramo 190 4.7 Conclusions 194 5 Analysis of the drought recovery of Andosols on southern Ecuadorian Andean páramos 197 5.1 Introduction 197 5.2 Materials 201 5.2.1 The study area 201 5.3 Monitoring of hydro-meteorological data 204 5.4 The measurement of the soil water content 205 5.5 Methods 206 5.5.1 The catchment modelling 206 5.5.2 The potential evapotranspiration 208 5.5.3 The actual evapotranspiration 208 5.5.4 Calibration and validation of the PDM model 209 5.5.5 The drought analysis 211 5.5.6 Drought propagation and drought recovery analysis 212 5.5.7 Vegetation stress and recovery 214 5.5.8 The soil water balance of the root zone 215 5.6 Results and discussion 217 5.6.1 Potential evapotranspiration 217 5.6.2 Modelling the discharge and the actual evapotranspiration 218 5.6.3 The drought severity 222 5.6.4 The drought propagation 224 5.6.5 Soil water drought recovery 226 5.6.6 The vegetation stress and recovery 228 5.6.7 Drought characteristics 231 5.6.8 The kv and ks coefficients and the critical soil water content 232 5.6.9 The Ea derived from soil water observations 234 5.7 Conclusions 235 6 Conclusions 239 6.1 Experimental hydrology in two undisturbed headwater Andean catchments 239 6.1.1 Multi-scale monitoring of the páramo ecosystem 240 6.1.2 Monitoring of the Andean tropical montane cloud forest of Portete 244 6.2 Experimental hydrology in a disturbed headwater Andean catchment 245 6.3 Water balance at the catchment scale 247 6.4 Application of the TOPMODEL concept in headwater Andean catchments 247 6.5 Analysis of the drought recovery of the Andosols on southern Ecuadorian Andean páramos 249 6.6 Perspectives of research 251 6.6.1 Experimental hydrology in Páramo and in TMCF 251 6.6.2 Hydrological modelling in Páramo and in TMCF 253 6.6.3 Catchment hydrology in disturbed headwater Andean catchments 254 References 255 Appendices 275 A: PHOTOS 275 B: Moisture retention data 281 C: Meteorological and hydrological data 283 D: The mathematical expressions of the FAO-Penman-Monteith approach 303 E: Scatter plots for the application of TOPMODEL 307 F: Photos of the páramo vegetation affected during the drought in 2009 311 List of publications 313nrpages: 316status: publishe