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Title:From groundwater to the atmosphere: using RELAMPAGO observations and modeling to understand changes in the hydrologic cycle of southeastern South America
Author(s):Pal, Sujan
Director of Research:Dominguez, Francina
Doctoral Committee Chair(s):Dominguez, Francina
Doctoral Committee Member(s):Nesbitt, Stephen W.; Kumar, Praveen; Gochis, David
Department / Program:Atmospheric Sciences
Discipline:Atmospheric Sciences
Degree Granting Institution:University of Illinois at Urbana-Champaign
Hydrologic modeling
Land surface modeling
Mesoscale convective systems
Abstract:Land-atmosphere interactions play an important role in modulating the hydroclimate of Southeastern South America (SESA). While climate variability and extreme events impact surface hydrology, the land surface of the region influences evapotranspiration, groundwater table depth, near-surface soil moisture and surface runoff. These surface conditions in turn affect the overlying atmosphere and precipitation. Understanding the hydrologic cycle, and its drivers at a regional scale are of particular interest as they are the key in assessing hydrometeorological consequences associated with climate and land surface variability. Past satellite studies have revealed thunderstorms that develop near the Andes Cordillera, and close to a smaller mountain range to the east (Sierras de Co ́rdoba), are some of the world’s deepest and most intense. This region of SESA features repeated days of deep convective events that have been linked to large hail, severe weather and flash flooding. The Remote sensing of Electrification, Lightning, And Mesoscale/microscale Processes with Adaptive Ground Observations (RELAMPAGO) campaign was aimed at understanding the processes of convective initiation, intensification, upscale growth, and storm propagation as well as the interaction between the subsurface, land and atmosphere in this region. The first part of this dissertation aims to characterize extreme hydrometeorological events and develop a modeling framework for streamflow hindcast and forecast, leveraging RELAMPAGO observations. Hydrological streamflow and meteorological observations in the previously ungauged mountainous basins of the Sierras de Co ́rdoba were performed to construct the stage-discharge curves in three basins and assess the suitability of satellite-based rainfall products. The critical findings from the observations were following: 1) flood response time in the river locations were found to be 5-6 hours, 2) satellite observed rainfall estimate Integrated Multi-satellite Retrievals for Global Precipitation Measurement-Final (IMERG-Final) performed better than other near-real-time products IMERG-Early and IMERG-Late, when compared with rain gauge estimates. The modeling component used the Weather Research and Forecasting (WRF) atmospheric model and its hydrologic component WRF-Hydro to create realistic hindcasts, deterministic forecasts, and a 60-member ensemble forecasts at sub-daily scale. The results of the modeling component demonstrated that streamflow simulations with regional-scale atmospheric data assimilation improved the accuracy of the forecasts. Findings from this part are being used by water managers in the region. The second part of this dissertation examines the connections between land use and surface-subsurface hydrology in the flat agricultural regions of SESA. Since the 1970s, there has been a dramatic expansion of annual crops in SESA as natural grasses and alfalfa pastures have been converted to soy, corn and other annual crops. RELAMPAGO observations over a soy site and an experimental alfalfa site in Marcos Juarez, Argentina reveal that soy has lower evapotranspiration and specific humidity, higher sensible heat, higher outgoing shortwave radiation and soil temperature compared to alfalfa. Additionally, the water table is shallower below soy. The Noah-MP land surface model was calibrated for the soy and alfalfa sites in Marcos Juarez. Long-term point-scale idealized Noah-MP simulations over soy and alfalfa revealed that evapotranspiration is the dominant component of the water budget (95% of precipitation) in alfalfa. In contrast, soy has a significant amount of recharge (28%) and runoff (4%) with reduced evapotranspiration (68%). This indicates the potential contribution of land use change in the observed increasing trend in streamflow and decreasing trend in water table depth. Results from this part of the study have implications for increased tendency of inland flooding and increasing streamflow due to agricultural expansion in SESA. The third part investigates the impacts of the above described land use change on the atmosphere. Regional simulations with the Noah-MP land surface model, both uncoupled and coupled to the atmospheric model WRF, were performed with idealized soy (representing current) and idealized alfalfa (representing historic) conditions (SOY and ALFALFA, respectively) in SESA. The uncoupled simulations suggested that a significant part of SESA has warmer (higher sensible heat) and drier (less latent heat) springs in the SOY scenario. Additionally, a domain-wide increase in soil moisture was found in the SOY scenario due to shallower water table. Coupled simulations indicate higher near-surface temperature, lower humidity, and reduced net radiation under SOY condition. Additional high-resolution ensemble WRF simulations were performed to simulate three extreme hydrometeorological events during the Spring of 2018. The storms were significantly larger and produced heavier precipitation under SOY conditions, highlighting the potential of land use changes to modify organized deep convective storms and extreme precipitation in SESA. The results from this part have implications for understanding the potential role of land use changes in the observed increasing trends of extreme rainfall over SESA.
Issue Date:2021-04-19
Rights Information:Copyright 2021 Sujan Pal
Date Available in IDEALS:2021-09-17
Date Deposited:2021-05

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