Huilin Gao

• Texas A&M University

The availability of surface water in global drylands is essential for both human society and ecosystems. However, the long-term drivers of change in surface water storage, particularly those related to anthropogenic activities, remain unclear. Here we use multi-mission remote sensing data to construct monthly time series of water storage changes fr...

Extreme daily evaporation from reservoir surfaces can lead to significant short-term water losses, affecting water quality, water supply, and reservoir operation strategies. Historical trends in daily reservoir evaporation events have eluded the scientific and operational communities, largely due to a lack of long-term, consistent data record. This...

Open water evaporation, which often consumes a large fraction of annual storage (especially in arid and semi‐arid regions), is a controlling variable for modern water resource management. Developing a daily reservoir evaporation data set is necessary for reservoir operations to consider the influence of evaporation in a timely manner. However, over...

This paper provides a review and summary status of the research underway by the NASA Terra Aqua Suomi-NPP Land Discipline Team to provide continuity of global land data products from the NASA Moderate resolution Imaging Spectroradiometer (MODIS) to the Visible Infrared Imaging Radiometer Suite (VIIRS). The two MODIS instruments on the NASA Earth Ob...

Reservoirs play a crucial role in regulating water availability and enhancing water security. Here, we develop NASA’s Visible Infrared Imaging Radiometer Suite (VIIRS) based Global Water Reservoir (GWR) product, consisting of measurements of reservoir area, elevation, storage, evaporation rate, and evaporation loss for 164 large global reservoirs....

Plain Language Summary Reservoirs are the prime source of water during droughts. However, water supply from reservoirs depends on how much water reservoirs have. Reservoirs lose significant amounts of water through evaporation. Hence, understanding reservoir droughts by incorporating evaporation information—will help water managers to better regula...

Climate change and increasing water demand due to population growth pose serious threats to surface water availability. The biggest challenge in addressing these threats is the gap between climate science and water management practices. Local water planning often lacks the integration of climate change information, especially with regard to its imp...

Reservoir evaporation is a critical component of water budgeting and operations but is often overlooked or simplified due to the difficulty in obtaining consistent, accurate estimates. Historically, reservoir evaporation estimation throughout Texas has relied on pan evaporation methods that are known to have large bias and uncertainty (Friedrich et...

Enhanced reservoir evaporation has become an emerging concern regarding water loss, especially when compounded with the ever-increasing water demand. In this study, we evaluated the evaporation rates and losses for 678 major reservoirs (representing nearly 90% of total storage capacity) in the CONUS over historical baseline (1980–2019), near-term (...

The warming climate is likely to increase hurricane-associated extreme rainfall and lead to sea-level rise (SLR). Thus, how the floods induced by intense hurricanes respond to these potential changes is of great concern. This study investigates the future warmer climate impacts on hurricane-induced extreme rainfall, and—more importantly—the subsequ...

Integrated forecasting systems for precipitation, streamflow, and floodplain inundation are of critical importance in mitigating the impacts of destructive floods caused by extreme weather events. However, the skills of streamflow and floodplain inundation forecasts derived from various Quantitative Precipitation Forecast (QPF) require a greater le...

To derive shallow water bathymetry for coastal areas, a common approach is to deploy a scanning airborne bathymetric light detection and ranging (LiDAR) system or a shipborne echosounder for ground surveys. However, recent advancements in satellite remote sensing, including the Ice, Cloud and land Elevation Satellite-2 (ICESat-2) offer new tools fo...

Drought can significantly impair water availability, agricultural productivity, ecosystem health, and the economy. The advent of satellite remote sensing has meant that reservoirs can be observed from space, which offers a unique promise for monitoring hydrological drought. Thus, the overarching goal of this chapter is to review and explore how the...

As the largest renewable energy source, hydropower is essential to the sustainability of the global energy market. However, a considerable amount of water can be lost in the form of evaporation from the associated multipurpose reservoirs, and hence enlarge the blue water footprint (BWF) of hydropower in a warming climate. To facilitate the sustaina...

Global reservoir information can not only benefit local water management but can also improve our understanding of the hydrological cycle. This information includes water area, elevation, and storage; evaporation rate and volume values; and other characteristics. However, operational wall-to-wall reservoir storage and evaporation monitoring informa...

Area-Volume-Elevation (AVE) curves are critical for reservoir operation rules. However, such curves are not publicly available for most global reservoirs. Here we present a framework to derive reservoir AVE curves from TanDEM-X data, using Lake Mead (~600 km 2) as an example. First, the maximum water extent from 1984 to 2018-provided by the Global...

Global lake evaporation is a critical component of the terrestrial water cycle. Accurate quantification of lake evaporation dynamics is of high importance for understanding lake energy budgets, land-atmosphere interactions , as well as regional water availability. However, the accurate quantification of lake evaporation has been hindered by the com...

The increased occurrence of flood events resulting from urbanization and global climate change is a great threat to water security. To systematically evaluate the impacts of urbanization on floods, we applied a paired catchments approach to two adjacent river basins in south-central Texas — the San Antonio River Basin (SARB), with fast urbanization...

Glacier retreat and runoff increases in the last few decades characterize conditions in the Kumalak River Basin, which is a headwater basin of the Tarim River with a catchment area of 12,800 km2. To address the scientific question of whether, and to what extent, the observed runoff increase can be attributed to enhanced glacier melt and/or increase...

Nine years after the Deepwater Horizon (DwH) oil spill (April 20, 2010 to July 15, 2010), the recovery of primary productivity at the ocean surface remains to be investigated. Here, we used the normalized fluorescence line height (nFLH) from the Moderate Resolution Imaging Spectroradiometer (MODIS) as an indicator of chlorophyll a concentration (Ch...

Knowledge of reservoir bathymetry is essential for many studies on terrestrial hydrological and biogeochemical processes. However, there are currently no cost-effective approaches to derive reservoir bathymetry at the global scale. This study explores the potential of generating high-resolution global bathymetry using elevation data collected by th...

Evaporation from open surface water is a critical and continuous process in the water cycle. Globally, evaporation losses from reservoirs are estimated to be greater than the combined consumption from industrial and domestic water uses. However, this large volume of water loss is only coarsely considered in modern water resources management practic...

Accurate and reliable hydrologic simulations are important for many applications such as water resources management, future water availability projections and predictions of extreme events. However, the accuracy of water balance estimates is limited by the lack of large-scale observations, model simulation uncertainties and biases related to errors...

The potential of using Landsat for assessing long-term water surface dynamics of individual reservoirs at a global scale has been significantly hindered by contaminations from clouds, cloud shadows, and terrain shadows. A novel algorithm was developed toward the automatic correction of these contaminated image classifications. By applying this algo...

Accurate and reliable hydrologic simulations are important for many applications such as water resources management, future water availability projections and predictions of extreme events. However, the accuracy of water balance estimates is limited by the lack of observations at large scales and the uncertainties of model simulations due to errors...

Offshore gas seeps may deteriorate marine water quality, causing negative effects on the sustainability of the coastal environment. Meanwhile, the Gulf Stream is a warm and swift Atlantic ocean current that may also impact the coastal water quality. The chlorophyll-a (Chl_a) concentration is one of the key indicators of marine water quality. The ob...

The advent of remote sensing makes it possible to monitor reservoir storages from space.Information from multi-satellite data – past and future – can be leveraged to improve the accuracy and temporal coverage of reservoir storage estimations.The objective of this study is to use Lake Mead as a testbed for comparing the effects of different satellit...

In just the past 5 years, the field of Earth observation has progressed beyond the offerings of conventional space-agency-based platforms to include a plethora of sensing opportunities afforded by CubeSats, unmanned aerial vehicles (UAVs), and smartphone technologies that are being embraced by both for-profit companies and individual researchers. O...

Freshwater availability and agricultural production are key factors for sustaining the fast growing population and economy in the state of Texas, which is the third largest state in terms of agricultural production in the United States. This paper describes a long-term (1918–2011) grid-based (1/8°) surface hydrological dataset for Texas at a daily...

In just the past five years, the field of Earth observation has evolved from the relatively staid approaches of government space agencies into a plethora of sensing opportunities afforded by CubeSats, Unmanned Aerial Vehicles (UAVs), and smartphone technologies that have been embraced by both for-profit companies and individual researchers. Over th...

During the past several decades, numerous reservoirs have been built across the world for a variety of purposes such as flood control, irrigation, municipal/industrial water supplies, and hydropower generation. Consequently, the timing and magnitude of natural streamflow have been altered significantly by reservoir operations. In addition, the hydr...

Flood mitigation in developing countries has been hindered by a lack of near real-time reservoir storage information at high temporal resolution. By leveraging satellite passive microwave observations over a reservoir and its vicinity, we present a globally applicable new algorithm to estimate reservoir storage under all-weather conditions at a 4 d...

A thorough understanding of the peak flows under urbanization and climate change-with the associated uncertainties-is indispensable for mitigating the negative social, economic, and environmental impacts from flooding. In this paper, a case study was conducted by applying the Distributed Hydrology Soil Vegetation Model (DHSVM) to the San Antonio Ri...

With its headwaters in the water towers of the western Cordillera of North America, the Fraser River is one of the continent’s mightiest rivers by annual flows, supplies vital freshwater resources to populous downstream locations, and sustains the world’s largest stocks of sockeye salmon along with four other salmon species. Here we show the Variab...

Land surface temperatures (LSTs) within tropical forests contribute to climate variations. However, observational data are very limited in such regions. This study used passive microwave remote sensing data from the Special Sensor Microwave/Imager (SSM/I) and the Special Sensor Microwave Imager Sounder (SSMIS), providing observations under all weat...

Freshwater availability and agricultural production are key factors for sustaining fast growing regions such as Mexico and Texas. Although future climate trends in temperature and radiative budget have been well investigated by the science community, our knowledge about the potential alterations of agroclimate and surface hydrology is strikingly li...

Man-made reservoirs play a key role in the terrestrial water system. They alter water fluxes at the land surface and impact surface water storage through water management regulations for diverse purposes such as irrigation, municipal water supply, hydropower generation, and flood control. Although most developed countries have established sophistic...

A source-oriented Community Multiscale Air Quality (CMAQ) model driven by the meteorological fields generated by the Weather Research and Forecasting (WRF) model was used to study the dry and wet deposition of nitrate (NO3(-)), sulfate (SO4(2-)), and ammonium (NH4(+)) ions in the Jiuzhaigou National Nature Reserve (JNNR), China from June to August...

The majority of liquid surface freshwater globally is stored in large lakes and reservoirs. However, consistent observations of lakes and reservoirs are very limited, which makes it challenging to assess the surface water effect on global weather forecasting, earth system modeling, water management planning, and ecosystem sustainability. The advanc...

Reservoir storage information is essential for accurate flood monitoring and prediction. South Asia, however, is dominated by international river basins where communications among neighboring countries about reservoir storage and management are extremely limited. A suite of satellite observations were combined to achieve high‐quality estimation of...

This paper presents an application of the Variable Infiltration Capacity (VIC) model to the Fraser River basin (FRB) of British Columbia (BC), Canada, over the latter half of the twentieth century. The Fraser River is the longest waterway in BC and supports the world's most abundant Pacific Ocean salmon populations. Previous modeling and observatio...

The implementation of a multimodel drought monitoring system is described, which provides near-real-time estimates of surface moisture storage for the global land areas between 50 degrees S and 50 degrees N with a time lag of about 1 day. Near-real-time forcings are derived from satellite-based precipitation estimates and modeled air temperatures....

Human alteration of the land surface hydrologic cycle is substantial. Recent studies suggest that local water management practices including groundwater pumping and irrigation could significantly alter the quantity and distribution of water in the terrestrial system, with potential impacts on weather and climate through land atmosphere feedbacks. I...

Water is essential to life, and it is central to society's welfare and sustainable economic growth. Consistent documentation of the water cycle and its changes over time is needed by the users of water cycle data - water managers, and those involved in related socio-economic sectors. However, observation-based records are often insufficient (especi...

Reservoir management is a key human activity that affects water resources over land. Some studies suggest that filling of reservoirs may have reduced sea level rise as much as 30 millimeters since the era of large dam construction began about 80 years ago. However, observations of reservoir storage are limited mostly to developed countries, and eve...

Over the last 40 years, Lake Chad, once the sixth largest lake in the world, has decreased by more than 90% in area. In this study, we use a hydrological model coupled with a lake/wetland algorithm to simulate the effects of lake bathymetry, human water use, and decadal climate variability on the lake's level, surface area, and water storage. In ad...

The potential utility of the real-time Tropical Rainfall Measuring Mission (TRMM) Multisatellite Precipitation Analysis real-time product 3B42RT (TMPA-RT) data for streamflow prediction, both through direct comparisons of TMPA-RT estimates with a gridded gauge product and through evaluation of streamflow simulations over four tributaries of La Plat...

Aims In the mid- and high-latitude regions, three quarters of the land surface is covered by boreal conifer forests, and snow lasts for 6–8 months of the year. Correctly modeling surface energy balance and snowmelt at mid- and high-latitudes has a significant influence on climate and hydrological processes. However, the heterogeneous and clumped fo...

During the last 40 years, Lake Chad, once the fourth largest lake in Africa, has lost more than 90% of its surface area. Various studies have suggested that the shrinking is due to either or both persistent droughts and a substantial increase in (unsustainable) irrigation. However, it remains unexplained why Lake Chad is more vulnerable than most o...

Nine satellite-based products, each of which provides information about land surface water budget terms, are used to estimate seasonal and annual variations in the water budget of the major river basins of the conterminous USA from 2003 to 2006. The remotely sensed terms are compared with gridded gauge precipitation, and estimates of evapotranspira...

We calculate evapotranspiration (E) from remote sensing (RS) data using the Penman–Monteith model over continental USA for four years (2003–2006) and explore, through an ensemble generation framework, the impact of input dataset (meteorological, radiation and vegetation) selection on performance (uncertainty) at the monthly time-scale. The impact o...

Terrestrial water storage (TWS) is a fundamental component of the water cycle. On a regional scale, measurements of terrestrial water storage change (TWSC) are extremely scarce at any time scale. This study investigates the feasibility of estimating monthly-to-seasonal variations of regional TWSC from modeling and a combination of satellite and in...

This document describes the algorithms within the latest version of the variable infiltration capacity (VIC) model. As a semi-distributed macroscale hydrological model, VIC balances both the water and surface energy within the grid cell; and its sub-grid variations are captured statistically. Distinguishing characteristics of the VIC model include:...

Consistent, long-term Earth System Data Records (ESDRs) for the terrestrial water cycle are needed to provide a basis for estimating the mean state and variability of the land surface water cycle for the major global river basins and the global terrestrial hydrosphere. For consistency, the ESDRs for each component must be done within a framework th...

Although lakes and reservoirs play a major role in the hydrology of the land surface over substantial areas of the globe, coherent information about their dynamics is largely lacking. The quality and completeness of information from in situ sources varies tremendously for different countries and regions. Recently, satellite data has provided some i...

Satellite remote sensing is a viable source of observations of land surface hydrologic fluxes and state variables, particularly in regions where in situ networks are sparse. Over the last 10 years, the study of land surface hydrology using remote sensing techniques has advanced greatly with the launch of NASA's Earth Observing System (EOS) and othe...

The extent of evapotranspiration (ET) over the Brazilian Amazon rainforest remains uncertain because in situ measurement sites do not cover the entire domain, and the fetch of these sites is only of the order of 10 m. In this investigation we developed an empirical method to estimate ET over the Brazilian Legal Amazon (BLA). The work was based on a...

The magnitude of the key terms in the terrestrial water balance at global and continental scales is surprisingly poorly known. Neither in situ observations nor land surface modeling is of sufficient accuracy to close the water balance through independent estimates of the terms. Remote sensing provides a basis for near-independent estimation of some...

A multi-sensor/multi-platform approach to water and energy cycle prediction is demonstrated in an effort to understand the variability and feedback of land surface and atmospheric processes over large space and time scales. Remote sensing-based variables including soil moisture (from AMSR-E), surface heat fluxes (from MODIS) and precipitation rates...

Remote sensing of land surface temperature (LST) using infrared (IR) sensors, such as the Moderate Resolution Imaging Spectroradiometer (MODIS), is only capable of retrieval under clear-sky conditions. Such LST observations over tropical forests are very limited due to clouds and rainfall, particularly during the wet season and high atmospheric wat...

We aim to develop consistent, long-term Earth System Data Records (ESDRs) for the major components (storages and fluxes) of the terrestrial water cycle at a spatial resolution of 0.5 degrees (latitude-longitude) and for the period 1950 to near-present. The resulting ESDRs are intended to provide a consistent basis for estimating the mean state and...

Assimilating soil moisture from satellite remote sensing into land surface models (LSMs) has potential for improving model predictions by providing real-time information at large scales. However, the majority of the research demonstrating this potential has been limited to datasets based on either airborne data or synthetic observations. The limite...

The estimation of regional evapotranspiration (ET) over Amazonia remains uncertain since there are very few in situ observational with a limited footprint (~1km). The present work uses an empirical method to estimate ET over the Brazilian Legal Amazon (BLA) based on satellite measurements. Satellite data include the Enhanced Vegetation Index (EVI)...

Passive microwave remote sensing has been recognized as a potential method for measuring soil moisture. Combined with field observations and hydrological modeling brightness temperatures can be used to infer soil moisture states and fluxes in real time at large scales. However, operationally acquiring reliable soil moisture products from satellite...

A Land Surface Microwave Emission Model (LSMEM) is used to derive soil moisture estimates over Iowa during the Soil Moisture Experiment 2002 (SMEX02) field campaign, using brightness temperature data from the Advanced Microwave Sounding Radiometer (AMSR)-E satellite. Spatial distributions of the near-surface soil moisture are produced using the LSM...

Each soil moisture data set is characterized by its specific mean value, variability, and dynamical range. For the assimilation of soil moisture observations into numerical models observation operators have to be developed, which reduce systematic differences. In this study, cumulative distribution function (CDF) matching is used to derive observat...

Coupled with information from the North American Land Data Assimilation System (NLDAS), standard soil datasets and vegetation and land surface parameters, a land surface microwave emission model (LSMEM) is employed using AMSR-E brightness temperatures at X-band (10.7 GHz) to determine soil moisture over Iowa for June and July 2002. Comparisons of c...

Assimilation of remote sensing data into hydrological modeling has the potential to improve forecasting accuracy; with space-borne, low frequency microwave observations being especially interesting because of its sensitivity to surface soil moisture and its change. However, in conveying the soil moisture information to land surface models, both the...

Soil moisture images for the Southern Great Plains Hydrology Experiment (SGP99) were derived from airborne passive microwave measurements obtained from the electronically scanned thinned array radiometer (ESTAR) and the polarimetric scanning radiometer (PSR) at L-band and C-band, respectively. In order to mimic operational products, a robust retrie...

The 1999 Southern Great Plains Hydrology Experiment (SGP99) provides comprehensive datasets for evaluating microwave remote sensing of soil moisture algorithms that involve complex physical properties of soils and vegetation. The Land Surface Microwave Emission Model (LSMEM) is presented and used to retrieve soil moisture from brightness temperatur...

The southern Great Plains region of the US has been a focus area for experimental remote sensing of surface soil moisture since the 1970's. Intercomparison of soil moisture retrieval using both experimental data and operational data is carried out during the SGP99 remote sensing campaign in July 1999. Passive microwave measurements obtained from th...

The lack of continuous soil moisture fields at large spatial scales, based on observations, has hampered hydrologists from understanding its role in weather and climate. The most readily available observations from which a surface wetness state could be derived is the Tropical Rainfall Measuring Mission (TRMM) Microwave Imager (TMI) observations at...

Operational soil moisture products from passive microwave satellite remote sensing are expected to improve our understanding of land-atmospheric interactions. The Tropical Rainfall Measuring Mission (TRMM) satellite launched in November, 1997, carries a microwave imager, offering one of two spaceborne sensors sensitive to soil moisture changes. The...

The estimation of state variables such as the soil moisture and surface temperature has been a key research area for many years. The importance of this information for land surface studies has motivated the development of different estimation techniques for these variables. Increasingly, there exists the capacity to independently determine componen...

Soil moisture, is an important factor in land-atmosphere interactions, and is crucial for understanding both the redistribution of radiant energy and the runoff generation/percolation of water in soil. To study climate change by using global models, calls for accurate input of soil moisture at large scales. Passive microwave remote sensing at C-ban...

The water cycle analysis is the most important part of the GEWEX project. In the water cycle analysis, the land surface wetness information plays an important role. TRMM/TMI is a new kind of microwave image unit, and has great potential application in land characteristics analysis, especially in remote sensing of land surface wetness information an...

An integrated modeling system that simulates the land surface water and energy states and resulting low-frequency microwave emissions is presented. The modeling system, combined with an explicit simulation of the orbital and scanning characteristics of a satellite sensor-antenna allows for carrying out Observing System Simulation Experiments (OSSEs...

The ability of the Tropical Rainfall Measuring Mission Microwave Imager (TRMM/TMI) for rainfall and flooding detection has been demonstrated in this study. A dynamic cluster K-mean method was presented to classify surface types and rain areas. Based on the TMI measurements and surface observations during the Huaihe River Basin Energy and Water Cycl...

This study investigates passive microwave remote sensing of surface soil moisture from three aspects: methods, results, and applications. A land surface microwave emission model (LSMEM) has been implemented to retrieve soil moistures from various remote sensing data. Chapter 2 introduces the physics and parameterization of the LSMEM algorithm. Base...