Tesis Doctorado

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Assessment of the impacts of climate change on the spatio-temporal patterns of freshwater sources to the coastal system of western Patagonia.
(Universidad de Concepción, 2023) Aguayo Gutierrez, Rodrigo Andres; Aguayo Arias, Mauricio
The western region of Patagonia is characterized by an almost pristine environment, with aquatic ecosystems composed of a great diversity of lakes, rivers and glaciers. The influence of westerly winds from the Southern Hemisphere results in high precipitation in the region, which determines large freshwater inputs to the coastal-marine system. In this vast (~400,000 km2), narrow (~200-300 km) and transboundary (Chile and Argentina) area, freshwater ecosystems interact with one of the most complex and extensive fjord systems in the world. In these systems, freshwater produces a pronounced vertical stratification of two or three layers, which is a key regulator of circulation patterns and primary production, and limits the depth of turbulent mixing. Turbulent mixing determines the exchange of nutrients between the different layers of the water column, a process that can trigger pulses of primary productivity and thus an increase in autotrophic biomass in the western Patagonian inland seas. Climate projections for most of Western Patagonia indicate a prolongation of the dry and warm conditions that have affected it in recent decades. Overall, the climate impacts recorded in Western Patagonia have been attributed to the Southern Annular Mode (SAM), which has shown a significant trend towards its positive phase. Given the heterogeneous and incomplete monitoring network of hydro-meteorological stations, most studies performed in this region have used only a very small subset of meteorological stations, satellite imagery or climate proxies to study environmental changes. Despite the low use of ground-based information, the region has shown evidence of a decrease in snow cover extent, an increase in forest fires, unusual tree growth patterns, a decrease in water availability and significant trends in major lakes, rivers and glaciers. Considering the threads posed by climate change scenarios, the main objective of the present doctoral thesis is to assess the impacts of anthropogenic climate change on the spatio-temporal patterns of freshwater inputs to the coastal system of western Patagonia. To this end, four specific objectives have been proposed, each associated with a different phase of the present thesis. The first objective explored the main trends, challenges and gaps in hydrological drought projections, using northern Patagonia (40-45ºS) as a study case. For this purpose, historical severe droughts and their climatic drivers in northern Patagonia were evaluated. In addition, a hydrological model was calibrated using a combination of satellite, reanalysis and groundbased data. To assess the impact of climate change on future severe droughts, 90 scenarios were used to account for multiple sources of uncertainty in the climate impact modeling chain. The projections obtained with the Coupled Model Intercomparison Project (CMIP) 6 and CMIP5 models showed significant climatic (greater trends in summer and autumn) and hydrological (longer droughts) differences, and therefore it is recommended that future climate impact assessments adapt the new simulations as more CMIP6 models become available. Based on the detected hydrological gaps, the second objective was to develop PatagoniaMet (PMET) to analyze the hydrological consistency between atmospheric reanalysis models, ground-based meteorological observations and stream gauges. PMET is a compilation of ground-based hydrometeorological data (PMET-obs), and a daily gridded product of precipitation and maximum and minimum temperature (PMET-sim). PMET-obs was developed considering a 4-step quality control process applied to 523 hydrometeorological time series obtained from eight institutions in Chile and Argentina, while PMET-sim used statistical bias correction procedures, spatial regression models and hydrological methods. PMET-sim was compared against other bias-corrected alternatives using hydrological modelling, and achieved Kling-Gupta efficiencies greater than 0.7 in 72% of the catchments, while other alternatives exceeded this threshold in only 50% of the catchments. Considering the hydrological importance of glaciers in the region and their uncertain evolution, the third objective used the Open Global Glacier Model (OGGM) to estimate the evolution of each glacier (area > 1 km2) in the Patagonian Andes (40-56°S) over the period 1980-2099. To generate these projections, different glacier inventories (n = 2), ice thickness datasets (n = 2), reference climates (n = 4), general circulation models (n = 10), emission scenarios (n = 4), and bias correction methods (n = 3) were used to disentangle the importance of different sources of uncertainty from a hydrological perspective. Overall, the projections suggest that the northern area is expected to experience a steady decline, while the Patagonian Icefields should increase or maintain their glacier runoff in the coming decades. Considering the melt on glacier signatures, the future sources of uncertainty (GCMs, SSPs and BCMs) were the main source in only 18% ± 21% of the total catchment area. In contrast, the reference climate was the most important source in 78% ± 21% of the catchment area, highlighting the importance of the second objective. Based on recent advances in regional and global datasets (second objective), and the potential trajectory of evolution of each glacier in the Patagonian Andes (third objective), the fourth objective generated state-of-the-art projections of freshwater inputs to the coastal system. Specifically, Long Short-Term Memory (LSTM) neural networks in combination with the Open Global Glacier Model (OGGM) were used to estimate the runoff evolution from non-glacier and glacier areas, respectively. The total runoff of the study area was 23,533 ± 1,399 m3 s-1 in the historical period (1985-2019). From this total, the glacier runoff contributed 5,185 ± 471 m3 s-1. While the northern area is expected to experience the greatest relative reductions with values close to -22%, the central and southern areas are expected to show slight increases with relative changes of 6% and 13% (Figure 6.1), respectively. Finally, the results showed in this thesis provides: i) a basis for an open collaborative dataset that outperforms all current alternatives, ii) the first large-scale evaluation of the impact of various sources of uncertainty (historical and future) beyond future glacier mass loss, and iii) state-of-the-art projections of freshwater inputs to the coastal system that will contribute to future climate change adaptation plans for Western Patagonia.
Integrated assessment of climate change and land-use/land-cover change on floods: insighs from landscape configuration in a tropical basin.
(Universidad de Concepción., 2023) Hurtado Pidal, Jorge René; Aguayo Arias, Mauricio; Link Lazo, Oscar
Climate change and land-use/land-cover change (LUCC) are among the main anthropogenic factors affecting flood risk, as they change the frequency and magnitude of floods. Specifically, native forest deforestation in tropical humid basins reduces the forest capacity for flood regulation during small and medium-size storms events. Also, while climate change affects at regional scales, the LUCC influences occur at a smaller, local scale. Consequently, forest protection and reforestation are considered a nature-based solutions (NbS) for flood regulation, especially on small basins (<100 Km2). However, there are few studies that analyze the combined effects of both forcings (i.e., climate change and LUCC) on floods, and generally they focus on the discharge at the basin outlet only. Thus, the continuous variation of interactions in the stream network has not been identified yet. On the other hand, little is known about the effects of different deforestation spatial patterns over floods. Together, these knowledge gaps limit the understanding of the ecosystem services provided by the forest for flood regulation within the context of NbS and climate change adaptation. Therefore, this research evaluates the effects of LUCC on floods distinguishing forest location and forest fragmentation in a humid tropical basin within the Ecuadorian Amazon. Additionally, it analyzes the individual and combined effects of climate change and LUCC on floods across the basin’s altitudinal gradient. In the first stage (Chapter III), this study applied the use of storm event sampling and flood-survey data to validate a modeling framework for flood hazard assessment in data-scarce watersheds. Specifically, the hydrologic modeling system (HEC-HMS) was coupled with the Nays2Dflood hydrodynamic solver to simulate the system response to several storm events including one, that flooded urban areas located within the basin. In the second stage (Chapter IV), the spatially-distributed hydrological model TETIS was calibrated and validated using nine storm samples in order to evaluate the effects of forest location and forest fragmentation on floods. The TETIS model was applied to simulate the influence of five LUCC scenarios, including forest location and forest fragmentation. The Kruskal-Wallis and the post-hoc Dunn tests were used to analyze the differences between scenarios. In the third stage (Chapter V), LUCC scenarios were prepared with two homogeneous land cover types, forest and agriculture, while precipitation scenarios were obtained through the Global Climate Model (GCM) IPSL SSP5-8.5 (CMIP6). The hydrological response of the scenarios was evaluated at 42 points across the stream network using the TETIS model previously calibrated. The individual and combined effects of climate change and LUCC were analyzed using absolute differences and the aforementioned statistical tests, including the Sheirer-Ray-Hare test. Results from the coupled approach, showed satisfactory model performance in simulating streamflow and water depths. In almost all events, the Nash-Sutcliffe coefficient (NSE) was within the range 0.40 ≤ NSE ≤ 0.95, while the range of Percent Bias (PBIAS) was −3.67% ≤ PBIAS ≤ 23.4%. Forest location and forest fragmentation had greater influence on overland flow than on stormflows at the basin outlet. However, forest location had more influence than forest fragmentation over both, overland flow and storm flows. Deforestation of the upper basin represented the worst scenario for flood regulation. In addition, the climate change effect on floods was more homogeneous than the LUCC effect, across the altitudinal gradient of the basin. Moreover, the relative influence of deforestation on stormflows was greater than that of climate change in the upper part of the basin, while in the lower part of the basin, the climate change was more important than LUCC for flood changes. For small floods the altitudinal range from 590 to 906 meters above sea level (m.a.s.l) was identified as a transitional area in terms of influence of deforestation on stormflows. However, a relatively stable threshold of absolute differences in peak flows and stormflow volume was obtained at 590 m.a.s.l. Finally, a slightly and statistically non-significant interaction between climate change and LUCC was identified, with an antagonistic effect in the lower part. In conclusion, native forest protection and/or reforestation, in the upper part of the basin are crucial for flood risk mitigation during small and moderate events, while maintaining several ecosystems services through implementation of NbS. The flood magnitude changes in the lower part of the basin are closely related to the scale effect and the sensitivity of the ecosystem in the upper part. Moreover, the importance of forest for flood regulation will be even greater in the future due to the climate change-induced precipitation projections. However, as storm intensity and catchment area increases, the capacity of forest to regulate floods decreases in the downstream direction and in a non-linear manner. Thus, the NbS needs to be integrated to other strategies within a broader context in order to achieve an effective flood management. The applied methodology can be used by modelers and decision-makers for flood impact assessment under climate change and LUCC scenarios in data-scarce watersheds. Moreover, the results improve our understanding of ecosystem services of Andean foothills forests and provide guidelines to implement NbS for flood regulation and climate change adaptation.

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