Publications

Check our peer-reviewed journal papers and conference papers.

Combined Use of Crop Yield Statistics and Remotely Sensed Products for Enhanced Simulations of Evapotranspiration within an Agricultural Watershed

Agricultural Water Management

April 1, 2022

Predicting water cycling in agricultural watersheds is challenging due to factors like farming practices. This study looks at using remote sensing evapotranspiration (ET) data and crop yield information to improve the accuracy of the Soil and Water Assessment Tool (SWAT) model. By adding more constraints to the model, such as crop yield, the number of acceptable parameter sets was reduced, and the model's performance improved. The results suggest that using crop yield data as an additional constraint can help reduce uncertainty and increase the accuracy of ET predictions in agricultural watersheds.

First Attempt of Global-Scale Assimilation of Subdaily Scale Soil Moisture Estimates from CYGNSS and SMAP into a Land Surface Model

Environmental Research Letters

July 1, 2021

Soil moisture is important for understanding the global water cycle, but current satellite measurements are not continuous in time or space. This study combines data from NASA's Cyclone Global Navigation Satellite System (CYGNSS) and the Soil Moisture Active Passive (SMAP) to improve soil moisture estimates in a land surface model (LSM). The results show a 61.3% improvement in LSM soil moisture accuracy when combining the two satellite systems. However, using satellite data in areas with dense vegetation can lead to less accurate results. This research is the first to use global GNSS-based soil moisture observations in LSMs, which can help fill gaps in soil moisture measurements and improve our understanding of the water cycle.

Deep Learning Approach to Predict Peak Floods and Evaluate Socioeconomic Vulnerability to Flood Events: A Case Study in Baltimore, MD, U.S.A

2021 SIEDS

April 1, 2021

As the intensity and frequency of storm events are projected to increase due to climate change, local agencies urgently need a timely and reliable framework for flood forecasting, downscale from watershed to street level in urban areas. Integrated with property data with various hydrometeorological data, the flood prediction model can also provide further insight into environmental justice, which will aid households and government agencies’ decision-making. This study uses deep learning (DL) methods and radar-based rainfall data to predict the inundated areas and analyze the property quickly and demographic data concerning stream proximity to provide a way to quantify socioeconomic impacts. We expect that our DL-based models will improve the accuracy of forecasting floods and provide a better picture of which communities bear the worst burdens of flooding, and encourage city officials to address the underlying causes of flood risk.

Utility of Remotely Sensed Evapotranspiration Products to Assess an Improved Model Structure

Sustainability

February 1, 2021

Hydrologic models have some predictive uncertainty when used for real-world applications. This study looks at using remotely sensed evapotranspiration (RS-ET) data to evaluate improvements in the Soil and Water Assessment Tool (SWAT) model. By comparing the original SWAT model and an improved version (RSWAT), researchers found that both models performed similarly for daily streamflow and evapotranspiration at the watershed level. However, at the subwatershed level, RSWAT showed better results for daily evapotranspiration. This study shows that using RS-ET data can help increase the accuracy of model predictions and highlights the importance of remote sensing data in hydrologic modeling.

Assessment and Combination of SMAP and Sentinel-1A/B-Derived Soil Moisture Estimates With Land Surface Model Outputs in the Mid-Atlantic Coastal Plain, USA

IEEE Transactions on Geoscience and Remote Sensing

February 1, 2021

This research focuses on using satellite and modeled products to monitor soil moisture (SM) content and predict natural disasters such as droughts, floods, wildfires, landslides, and dust outbreaks. The study validates three SMAP SM products with in-situ data using conventional and triple collocation analysis (TCA) statistics and merges them with a Noah-Multiparameterization version-3.6 (NoahMP36) land surface model (LSM). An exponential filter and a cumulative density function (CDF) are used to evaluate the SM products. The study found that CDF-matched 9-, 3-, and 1-km SMAP SM data showed reliable performance with R and ubRMSD values of 0.658, 0.626, and 0.570 and 0.049, 0.053, and 0.055 m3/m3, respectively. Combining SMAP and NoahMP36 greatly improved R-values to 0.825, 0.804, and 0.795, and ubRMSDs to 0.034, 0.036, and 0.037 m3/m3, respectively. These findings suggest that SMAP/Sentinel data can improve regional-scale SM estimates and LSMs with improved accuracy.

Assessment of Drought Conditions over Vietnam using Standardized Precipitation Evapotranspiration Index, MERRA-2 re-analysis, and Dynamic Land Cover

Journal of Hydrology: Regional Studies

December 1, 2020

In recent years Vietnam has experienced historical drought events possibly affected by climate change, but the analysis is challenging due to lack of necessary observations for monitoring drought conditions. The goal of this study is to analyze the characteristics of droughts over a 30-year period, using three spatial-resolution MERRA-2 datasets in Vietnam. The Standardized Precipitation Evapotranspiration Index (SPEI) was used as an index for drought based on precipitation and temperature. We also estimated the impacts of drought on agriculture using annual land cover datasets.

* = mentored by Dr. Kim

Intercomparison and Combination of Inland Water Observations from CYGNSS, MODIS, Landsat, and High-Resolution Commercial Satellite Imagery

G. Pavur, H. Kim*, B. Fang, V. Lakshmi
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Major Revision

Streamflow Estimation in Ungauged Regions using Machine Learning: Quantifying Uncertainties in Geographic Extrapolation

M.H. Le, H. Kim*, S. Adam, H. X. Do, P.A. Beling, V. Lakshmi
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Major Revision

Temporal Gap-filling of 12-hourly SMAP Soil Moisture over the CONUS using Water Balance Budgeting

R. Zhang, S. Kim, H. Kim, A. Sharma, B. Fang, V. Lakshmi
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Major Revision

Systematic modelling errors undermine the application of land data assimilation systems for hydrological and weather forecasting

Wade T. Crow, Hyunglok Kim, and Sujay Kumar
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Under Review

Interpreting effective hydrologic depth estimates derived from soil moisture remote sensing: A Bayesian non-linear modelling approach

Hyunglok Kim and Wade T. Crow
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Under Review

Changes in the speed of the global terrestrial water cycle due to human interventions

Hyunglok Kim, Wade T. Crow, and Venkataraman Lakshmi
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Under Preperation

A Global Scale Analysis of Subsurface Scattering Signals Impacting ASCAT Soil Moisture Retrievals

Wolfgang Wagner, Roland Lindorfer, Sebastian Hahn, Hyunglok Kim, Mariette Vreugdenhil, Alexander Gruber, Milan Fischer, and Miroslav Trnka
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Under Review

Systematic Modeling Errors Strongly Undermine The Value Of Land Data Assimilation Systems And Microwave Remote Sensing For Water Flux Estimation

W. T. Crow, H. Kim , S. Kumar
IEEE International Geoscience and Remote Sensing Symposium
July 21, 2023

Utilizing Bayesian Machine Learning for Analyzing Error Patterns in Global-Scale Soil Moisture Data

H. Kim , W. T. Crow, W. Wagner, X. Li, V. Lakshmi
Hydrology Machine Learning (HydroML) Symposium, Phase 2 at Berkeley Lab
May 1, 2023

Uncertainty Analysis Framework in the Water Balance Equation Using Bayesian Statistical Modeling Approach

H. Kim, W. Crow
American Geophysical Union, Fall Meeting
December 1, 2022

Retrieving Runoff in Ungauged Basins using Satellite Observations of Rainfall and Soil Moisture

H. Kim, W. Crow
American Geophysical Union, Fall Meeting
December 1, 2022

Changes in Extreme Precipitation Patterns in the Meuse River Basin as a Driver of the July 2021 Flooding

B. Goffin, P. Kansara, H. Kim, V. Lakshmi
American Geophysical Union, Fall Meeting
December 1, 2022

Reconstruction of the SMAP-based 12-hourly soil moisture product over the CONUS through water balance budgeting

R. Zhang, S. Kim, H. Kim, B. Fang, A. Sharma, V. Lakshmi
American Geophysical Union, Fall Meeting
December 1, 2022

Hydrological flash drought forecasting using meteorological flash drought indices and machine learning approaches – A case study in the Mississippi River Basin

S. Bakar, D. Quintero, M. Le, H. Kim, S. S. Adams, P. Beling, V. Lakshmi
American Geophysical Union, Fall Meeting
December 1, 2022

Global downscaling and assimilation of soil moisture

V. Lakshmi, B. Fang, H Kim
IAHS2022
March 1, 2022

Impact of Land Use Land Cover Changes on Carbon and Water Cycle Interactions: Using Data Driven Modeling and Satellite Products

M. Umair, S. Khan, H. Kim, M. Azmat, S. Atif
American Geophysical Union, Fall Meeting
December 1, 2021

Water Cycle in Different Time Scales: Analyzing the Impact of Human-driven Changes in Land Cover using Bayesian Inferences and Data Assimilation Methods

H. Kim, V. Lakshmi
American Geophysical Union, Fall Meeting
December 1, 2021

Contact me

If you have a keen interest in the intersection of climate change and its impact on hydrological research fields, I encourage you to consider pursuing a Master's, PhD, or postdoctoral position. By delving deeper into this critical area of study, you can play an essential role in addressing the world's most pressing environmental challenges and help safeguard our water resources, ecosystems, and communities. Your dedication and expertise can significantly contribute to the development of sustainable solutions and innovative approaches to hydrological research. Embark on this exciting journey and become part of the passionate community of scientists working towards a more resilient and environmentally responsible future.