Browsing by Author "Ochoa Sánchez, Ana Elizabeth"

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Atmosphere-surface fluxes modeling for the high Andes: the case of páramo catchments of Ecuador
(2020) Carrillo Rojas, Galo José; Schulz, Hans Martin; Orellana Alvear, Johanna Marlene; Ochoa Sánchez, Ana Elizabeth; Trachte, Katja; Célleri Alvear, Rolando Enrique; Bendix, Jorg
© 2019 Elsevier B.V. Interest in atmosphere-surface flux modeling over the mountainous regions of the globe has increased recently, with a major focus on the prediction of water, carbon and other functional indicators in natural and disturbed conditions. However, less research has been centered on exploring energy fluxes (net radiation; sensible, latent and soil heat) and actual evapotranspiration (ETa) over the Neotropical Andean biome of the páramo. The present study assesses the implementation and parameterization of a state-of-art Land-Surface Model (LSM) for simulation of these fluxes over two representative páramo catchments of southern Ecuador. We evaluated the outputs of the LSM Community Land Model (CLM ver. 4.0) with (i) ground-level flux observations from the first (and highest) Eddy Covariance (EC) tower of the Northern Andean páramos; (ii) spatial ETa estimates from the energy balance-based model METRIC (based on Landsat imagery); and (iii) derived ETa from the closure of the water balance (WB). CLM's energy predictions revealed a significant underestimation on net radiation, which impacts the sensible and soil heat fluxes (underestimation), and delivers a slight overestimation on latent heat flux. Modeled CLM ETa showed acceptable goodness-of-fit (Pearson R = 0.82) comparable to ETa from METRIC (R = 0.83). Contrarily, a poor performance of ETa WB was observed (R = 0.46). These findings provide solid evidence on the CLM's accuracy for the ETa modeling, and give insights in the selection of other ETa methods. The study contributes to a better understanding of ecosystem functioning in terms of water loss through evaporative processes, and might help in the development of future LSMs’ implementations focused on climate / land use change scenarios for the páramo.
Evaluation of downscaled estimates of monthly temperature and precipitation for a Southern Ecuador case study
(2016) Ochoa Sánchez, Ana Elizabeth; Campozano Parra, Lenin Vladimir; Sánchez Cordero, Esteban Remigio; Gualan Saavedra, Ronald Marcelo; Samaniego Alvarado, Esteban Patricio
The downscaling of global climate models (GCMs) aims at incorporating finer scale information to their horizontal resolution in order to represent regional and local processes better. There are two main approaches to downscaling: statistical (based on data relationships between synoptic atmospheric variables and observations of local variables) and dynamical (based on the modelling of regional atmospheric processes and land-surface interactions). In this study, some predictive capabilities regarding the generation of station-scale mean monthly temperature and rainfall of both a statistical artificial neural network (ANN-based) and a dynamical weather research and forecasting (WRF-based) downscaling approach are assessed. We have devised two versions of the statistical downscaling approach. One of them includes regional orographic variables as predictors to allow for spatial extrapolation; the other is purely local. Historical observational data, from the period 1990 to 1999, of two major watersheds in the Ecuadorian Southern Andes, the Jubones and Paute river basins, were used. Since, to a certain extent, the value added by downscaling techniques can be attributed to terrain information, it is worth noting that some characteristics of the selected catchments (as notorious altitude differences and the presence of qualitatively different precipitation regimes) provide a scientifically interesting location for exploring how finer scale effects are captured. For this reason, we concentrate on the ability of downscaling techniques to reproduce seasonality. A decade of evaluation proved that both approaches were able to qualitatively describe precipitation and temperature seasonal variations for different regimes at representative weather stations. Furthermore, the seasonality of precipitation represented by both downscaling approaches surpassed the seasonality representation of reanalysis data. However, shortcomings on the estimates were found. Specifically, dynamical downscaled precipitation estimates were prone to overestimation. Despite the fact that the considered downscaling approaches are different in nature, their ability to represent the high spatio-temporal variability in this region highlights the importance of evaluating their strengths and limitations. © 2016 Royal Meteorological Society.
Evaporation dynamics and partitioning in Andean tussock grasslands
(Ed, 2022) Célleri Alvear, Rolando Enrique; Ochoa Sánchez, Ana Elizabeth; Crespo Sánchez, Patricio Javier; Carrillo Rojas, Galo José; Sucozhañay Calle, Adrián Esteban; Marín Molina, Franklin Geovanny; Ochoa Sánchez, Ana Elizabeth
The paramo biome, located above 3300 m a.s.l. and covered mainly by tussock grasslands, provides ecosystem services for Andean cities, especially water resources used for drinking water, agriculture, hydropower generation and sustaining aquatic ecosystems. Even though research about the main components of the water cycle has increased substantially in the last decade, evaporation has remained unknown. In this study, we quantified for the first time daily, monthly and annual evaporation, its components (i.e. interception and transpiration) at event scale and its climatic drivers at a representative páramo catchment in Southern Ecuador (Figure 1). We used the eddy-covariance method to quantify evaporation. We additionally compared those measurements with lysimeters, water balance, energy balance, hydrological models (HBV-light and PDM) and the calibration of the Penman-Monteith equation in order to find easier and cheaper alternatives for estimating evaporation at the páramo
Impact of tussock grass removal on the soil water dynamics of a tropical mountain hillslope
(2018-03-12) Montenegro Díaz, Paola Fernanda; Célleri Alvear, Rolando Enrique; Ochoa Sánchez, Ana Elizabeth
Soil water content (SWC) is related to the ecohydrological processes and environmental services of ecosystems. However, SWC studies are scarce in mountain humid ecosystems, such as the Andean páramos, where human activities can alter their SWC dynamics and perhaps their water regulation capacity. Our objective was to analyze the influence of extensive grazing in the SWC of an Andean páramo hillslope with native tussock grass vegetation. The SWC of a hillslope was monitored through paired water content reflectometers (WCRs) placed at different soil depths (10 – 75 cm) in eight soils profiles along two parallel transects. After 5 years the vegetation was cut out from one transect – as an emulation of extensive grazing – and both transects were monitored for 10 months. Changes in SWC were explored through differences in SWC between the paired WCRs during three subperiods after the experiment, selected according to the precipitation characteristics (amount, intensity and distribution). Immediately after the vegetation cut out (2 months) and during the dry subperiod (2 months) we noticed that in the superficial soil layer (10 cm depth) at the top and middle-top of the hillslope the SWC increased and decreased respectively, while their SWC spatio-temporal variability decreased. No impact was detected during the rainy subperiod, 8 months after the experiment. Nevertheless, these few changes were attributed to changes in interception and to grassroots death-regrowth. Results suggest that the impact of extensive grazing is low as long as the soils are not destroyed, especially during rainy periods.
Impact of tussock grasses removal on soil water content dynamics of a tropical mountain hillslope
(2019) Montenegro Díaz, Paola Fernanda; Ochoa Sánchez, Ana Elizabeth; Célleri Alvear, Rolando Enrique
© 2019 John Wiley & Sons, Ltd. Land use impacts on soil water content (SWC) are scarcely studied in mountain humid ecosystems, such as the Andean páramos, despite its influence on ecohydrological processes. Our objective was to analyze the impacts of extensive grazing on SWC of an Andean páramo hillslope with native tussock grasses. Along two parallel transects in a hillslope, we monitored SWC through pairs of SWC sensors placed at different soil depths (Ah horizon= 10 –35 cm; C horizon= 65 – 75 cm). The tussock grasses were cutout from one transect (Experimental) as an emulation of extensive grazing (without soil destruction), whereas the second transect (Control) remained intact. Both transects were hourly monitored for 10 months (post-intervention period). Post-intervention period was compared with a pre-intervention period of similar precipitation characteristics to minimize the influence of precipitation in the interpretation of the results. We analyzed both periods through differences in SWC between the pairs of sensors (Experimental minus Control) and differences in SWC dynamic of the pairs of sensors through linear regressions (slope and intercept values). Results suggest that the emulation did not change the mean SWC, but caused a reduction of SWC dynamic. Causes of SWC attenuation were a lower interception and transpiration, a higher amount of effective rainfall infiltrated, and similar evaporation from the soil than under unchanged conditions. These observations were done at all the soil depths. Probably, extensive grazing does not negatively affect the hydrological functioning of páramo ecosystems, particularly its water yield, as long as the soil remains undisturbed.
Importance of Fog and Cloud Water Contributions to Soil Moisture in the Andean Paramo
(2022) Berrones Guapulema, Gina Marcela; Célleri Alvear, Rolando Enrique; Wilcox, Bradford P.; Ochoa Sánchez, Ana Elizabeth; Crespo Sánchez, Patricio Javier
Páramos are particular ecosystems of the Tropical Andes, where fog and low-intensity rainfall such as drizzle are commonly frequent—but the contribution of these water sources to soil water replenishment and discharge is not yet clear, mainly because the development of techniques for separating fog from drizzle and wind-driven rainfall has been challenging. Fog was measured with a cylindrical Juvik gauge and types of precipitation other than fog with a high-resolution disdrometer. Soil moisture was measured at 100 mm depth by means of Water Content Reflectometers, then Effective precipitation (EP) was calculated. We categorized events as two types: fog only (FO) and cloud water (CW). We found that in the case of FO events, only small amounts reached the soil (EP ranged between 0.1 and 0.2 mm); in contrast, greater amounts of EP originated from CW events (maximum value of 4.3 mm). Although we found that FO events are negligible for stream water contribution; they are ecologically important for maintaining high relative humidity, low net radiation, and consequently low evapotranspiration rates. Our research provides new insights into the hydrological role of fog, enabling us to better understand to what extent its input influences the water resources of the Andean páramo.
Unraveling evapotranspiration dynamics and processes in tropical Andean tussock grasslands
(2019-10-15) Ochoa Sánchez, Ana Elizabeth; Célleri Alvear, Rolando Enrique
The páramo biome provides water resources for many cities in the Andes. These resources are used for drinking water, irrigation, hydropower generation and for sustaining aquatic ecosystems. Notwithstanding mountainous terrains place difficulties for their study, due to its remoteness and data scarcity, knowledge about the functioning of this biome has improved lately. Precipitation (P) and runoff monitoring has increased dramatically, but this was not the case for evapotranspiration (ETa). In order to understand the components of the hydrological cycle, this study aimed at understanding the evapotranspiration process of this important biome by pursuing the following three objectives: (1) to quantify interception, transpiration and their contribution to evapotranspiration, (2) to find suitable methods for measuring and estimating evapotranspiration, and (3) to investigate the controls on evapotranspiration. Results show the high contribution of interception to the evapotranspiration process. The maximum capacity of tussock grasslands to intercept water was 2 mm. During small events (P < 2 mm), between 100 and 80 % of precipitation was intercepted and released back to the atmosphere as vapour; while during large events (P > 2 mm), interception loss decreased from 80 to 10 %. Interception was mainly driven by precipitation amount and secondary by relative humidity. During dry periods, transpiration rates were on average 1.7 mm/day (ranging between 0.7 and 2.7 mm/day) and on top, the fog and dew harvested by the vegetation contributed to the evapotranspiration in around 30 %. For measuring evapotranspiration, the eddy-covariance method is considered the most accurate and with the highest resolution. However, given the high cost of the method, complex installation, operation and maintenance, two hydrological models (HBV-light and PDM) and the calibrated Penman-Monteith equation were found robust alternative methods for the daily estimation of evapotranspiration. These alternative methods are accurate (Pearson’s correlation coefficient > 0.7 and bias percentage < 20 %), freely available and easy to implement. This study also showed that the commonly used water balance method was not suitable for estimating evapotranspiration at daily or monthly scale. Finally, it was found that the páramo biome has a relatively low evapotranspiration rate (annual ETa/P = 0.5) and is an energy-limited site, where net radiation is the primer control on evapotranspiration (annual ETa/Rn = 0.47). The secondary controls were wind speed, surface and aerodynamic conductance, especially important during dry periods.
Unravelling evapotranspiration controls and components in tropical Andean tussock grasslands
(2020) Ochoa Sánchez, Ana Elizabeth; Crespo Sánchez, Patricio Javier; Carrillo Rojas, Galo José; Marín Molina, Franklin Geovanny; Célleri Alvear, Rolando Enrique
The study of the environmental factors that control evapotranspiration and the components of evapotranspiration leads to a better understanding of the actual evapotranspiration (ET) process that links the functioning of the soil, water and atmosphere. It also improves local, regional and global ET modelling. Globally, few studies so far focussed on the controls and components of ET in alpine grasslands, especially in mountainous sites such as the tussock grasslands located in the páramo biome (above 3300 m a.s.l.). The páramo occupies 35 000 km2 and provides water resources for many cities in the Andes. In this article, we unveiled the controls on ET and provided the first insights on the contribution of transpiration to ET. We found that the wet páramo is an energy-limited region and net radiation (Rn) is primarily controlling ET. ET was on average 1.7 mm/day. The monthly average evaporative fraction (ET/Rn) was 0.47 and it remained similar for wet and dry periods. The secondary controls on ET were wind speed, aerodynamic resistance and surface resistance that appeared more important for dry periods, where significantly higher ET rates were found (20% increase). During dry events, transpiration was on average 1.5 mm/day (range 0.7–2.7 mm/day), similar to other tussock grasslands in New Zealand (range 0.6–3.3 mm/day). Evidence showed interception contributes more to ET than transpiration. This study sets a precedent towards a better understanding of the evapotranspiration process and will ultimately lead to a better land-atmosphere fluxes modelling in the tropics. © 2020 John Wiley & Sons Ltd
Variabilidad espacio temporal de la calidad de agua a escala de microcuenca en zonas de páramo
(2009) Ochoa Sánchez, Ana Elizabeth; Rodas Ochoa, María Verónica; Pauta Calle, Gladys Guillermina