Tesis Doctoral/PHD

Permanent URI for this collectionhttps://dspace-test.ucuenca.edu.ec/handle/123456789/24267

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Bridging the gap between hydrological and biogeochemical processes in a high Andean catchment: a comprehensive tracer-aided model framework
(Universidad de Cuenca, 2023-09-29) Pesántez Vallejo, Juan Patricio; Crespo Sánchez, Patricio Javier; Birkel, Christian; Célleri Alvear, Rolando Enrique
The Andean mountains satisfy the vital needs of the Andean population and its lowlands. However, they are projected to experience significant impacts attributed to land-use change and climate change. Despite our understanding of the hydrology in these areas, to date, there has been no modeling framework that incorporates direct data acquisition, simple models, and extends to a distributed modeling framework. Such a framework should be able to elucidate hydrological and biogeochemical processes in a manner comprehensible to decision-makers. Therefore, the primary objective of this thesis is to spatially and temporally assess the production and distribution of water and dissolved organic carbon (DOC) in a páramo catchment using tracer-aided models. To achieve this, we have monitored hydrometeorological and biogeochemical parameters, as well as water stable isotopes. In combination with field observations and perceptual knowledge of these catchments, we evaluated them within a comprehensive hydrological modeling framework. We found that DOC and other solutes can be estimated through in-situ spectrometry. Using these solutes as tracers made it possible to compare different hydrological pathways and was the only way to identify that streamflow response consisted of near-surface rapid flow, more mixed flow through the two main soil types, as well as flow from shallow fractured rock, especially under base flow conditions. Based on the hydrological processes found, a new module was developed to simulate DOC production and incorporate it into a spatially distributed hydrological model at a high spatial (10 x 10 meters) and temporal (1 hour) resolution. This model allowed us to identify DOC hots pots and hot moments. The results showed increased hydrological connectivity between hillslopes and valleys with increasing precipitation. Wetter conditions also favored DOC production, especially in valleys (Histosols), and DOC transport to the river. Our findings suggest that minor changes in meteorological conditions directly affect water dynamics in páramo soils and its biogeochemistry. These conclusions will enable informed decisions to be made regarding water security, taking into account the effect of carbon loss from the soils to the rivers in the páramo.
Dynamics of Precipitation Anomalies in Tropical South America: A Multiscale Approach
(Universidad de Cuenca, 2023-05-08) Córdova Mora, Mario Andrés; Célleri Alvear, Rolando Enrique
This PhD thesis aims to study the dynamics of precipitation anomalies and extreme precipitation events in tropical South America (TrSA). Precipitation anomalies in TrSA are influenced by a complex climate variability resulting from the superposition of various phenomena acting on different temporal and spatial scales, as well as several geographical features. The study uses interpolated gridded global datasets and climate reanalysis to understand dynamics of precipitation anomalies, while weather radar data and last-generation reanalysis datasets were employed to investigate extreme precipitation events. The study applied data analysis techniques and machine learning algorithms and incorporated process knowledge to select the input data and interpret the results. Three objectives were executed to understand precipitation anomalies and extreme precipitation events in TrSA using a multiscale perspective: 1) understanding the dynamics of precipitation anomalies in tropical South America in annual to monthly scales, 2) understanding the dynamics of precipitation anomalies in the tropical Andes in seasonal scale, and 3) understanding the dynamics of extreme precipitation at event scale in the southern Ecuadorian Andes. The study found that precipitation anomalies are mainly influenced by the intensity and position of the South Atlantic Convergence Zone (SACZ), El Niño Southern Oscillation (ENSO), the meridional position of the Intertropical Convergence Zone (ITCZ), and the strength of the South American Monsoon System. Moreover, Convective Available Potential Energy (CAPE), the vertical integral of divergence of moisture flux, and SSTbased oceanic indices were found to be important variables that influence precipitation anomalies in different regions of the tropical Andes. Finally, the study found distinct patterns of circulation anomalies for extreme events in the southern Ecuadorian Andes.
Fog in the Andean Páramo: measurements, dynamics, and its influence on soil hydrology and evapotranspiration processes
(Universidad de Cuenca, 2022-09-15) Berrones Guapulema, Gina Marcela; Célleri Alvear, Rolando Enrique
The páramo ecosystem is characterized by a very moist climate and the continuous presence of fog and low-intensity rainfall. The most important páramo feature is the high water regulation capacity which in part might be related to the high frequency of fog and low-intensity rainfall (drizzle). Therefore, it is essential to understand the hydrological processes that are linked to the ecology of the páramo. This study aimed the following three objectives: (1) to assess fog water estimates derived from three different types of fog gauges, and from them to understand its temporal dynamics and the importance of fog to annual rainfall; (2) to quantify the contribution of fog water deposition to soil moisture; and (3) to analyze the impact of fog on evapotranspiration rates, under different weather conditions (clear, foggy and rainy). Findings of this study show that fog occurs at very low intensities (0.2 mm h-1) reporting events of short term (<3 hours) at wind velocities below 4 m s-1. Most of the time fog appears combined with other type of precipitation (i.e. drizzle, light rain or rain) with fog tending to be more intense in the early morning, and at night. On average, daily fog amounts 1.37 mm. Overall, fog and drizzle are the major water sources to páramo vegetation, especially during late night-time and early mornings, when evaporation is low. The fog water deposition shows that only 4.5% of fog reaches the soil, contributing to soil moisture changes rather low (0.1-0.2 mm), whilst the combination of fog with low-intensity rainfall generate a higher contribution on soil moisture (as high as 4.3 mm). These events are potentially important for both soil moisture and stream flow, because of their long duration and high total amount per-event. Daily evapotranspiration rates are reduced by 43% due to the presence of mixed conditions (fog + lowintensity rainfall) compared with clear conditions (no fog and no rainfall). The net radiation is reduced by 9.2% during foggy conditions (only fog) mainly because its early morning hours occurrence is higher, and when solar radiation peaks fog occurrence is lower. While, during mixed conditions the net radiation is reduced by 33%. At the same time as less humid periods were reported, evapotranspiration was also low; suggesting that fog and drizzle presence can inhibit transpiration, limit water loss by evaporation and also could alleviate water stress.
Towards the improvement of machine learning peak runoff forecasting by exploiting ground- and satellite-based precipitation data: A feature engineering approach
(Universidad de Cuenca, 2023-05-10) Muñoz Pauta, Paul Andrés; Célleri Alvear, Rolando Enrique; Orellana Alvear, Johanna Marlene
Peak runoff forecasting in complex mountain systems poses significant challenges in hydrology due to limitations in traditional physically-based models and data scarcity. However, the integration of machine learning (ML) techniques offers a promising solution by balancing computational efficiency and enabling the incorporation of satellite precipitation products (SPPs). However, debates have emerged regarding the effectiveness of ML in hydrology, as its black-box nature lacks explicit representation of hydrological processes, hindering performance improvement and result reproducibility. To address these concerns, recent studies emphasize the inclusion of FE strategies to incorporate physical knowledge into ML models, enabling a better understanding of the system and improved forecasting accuracy. This doctoral research aims to enhance the effectiveness of ML in peak runoff forecasting by integrating hydrological concepts through FE techniques, utilizing both ground-based and satellite-based precipitation data. For this, we explore ML techniques and strategies to enhance accuracy in complex macro- and mesoscale hydrological systems. Additionally, we propose a FE strategy for a proper utilization of SPP information which is crucial for overcoming spatial and temporal data scarcity. The integration of advanced ML techniques and FE represents a significant advancement in hydrology, particularly for complex mountain systems with limited or inexistent monitoring networks. The findings of this study will provide valuable insights for decision-makers and hydrologists, facilitating effective mitigation of the impacts of peak runoffs. Moreover, the developed methodologies can be adapted to other macro- and meso-scale systems, with necessary adjustments based on available data and system-specific characteristics, thus benefiting the broader scientific community.
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.

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Browsing Tesis Doctoral/PHD by Author "Célleri Alvear, Rolando Enrique"