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

Abstract

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.