Assessment and Development of Remotely Sensed Evapotranspiration Modeling Approaches

Remote sensing has been a promising approach to extracting distributed evapotranspiration (ET) information at varying spatial and temporal scales. Performances of several vegetation index (VI) based and remotely sensed surface energy balance (RSEB) models were evaluated to identify simple and accurate models and apply them to study ET variations from field to regional scales. A simple VI model using a single Landsat image to estimate annual ET was evaluated and successfully captured inter-annual riparian ET variations along a section of the Colorado River, U.S. The study showed the applicability of a simple and accurate approach for annual ET estimation with fewer data and resources. A modeling framework was developed to derive daily time series of ET maps using a RSEB model, satellite imagery, and ground-based weather data. The daily and annual ET maps obtained from the modeling framework successfully captured spatial and temporal ET variations across Oklahoma, U.S. The model also identified the regions that are more susceptible to droughts. Finally, five RSEB models were evaluated for their performance in estimating daily ET of winter wheat under variable grazing and tillage practices in central Oklahoma. The surface energy balance algorithm for land (SEBAL) had the best agreement whit eddy covariance estimates. The daily ET estimates from SEBAL captured the field-scale ET variations within grazing/tillage managements. All studies conducted based on VI and RSEB models over different land covers and spatial/temporal scales identified advantages and limitations of models and developed a framework to construct time series of ET maps, which has a wide range of applications

Mapping Annual Riparian Water Use Based on the Single-Satellite-Scene Approach

The accurate estimation of water use by groundwater-dependent riparian vegetation is of great importance to sustainable water resource management in arid/semi-arid regions. Remote sensing methods can be effective in this regard, as they capture the inherent spatial variability in riparian ecosystems. The single-satellite-scene (SSS) method uses a derivation of the Normalized Difference Vegetation Index (NDVI) from a single space-borne image during the peak growing season and minimal ground-based meteorological data to estimate the annual riparian water use on a distributed basis. This method was applied to a riparian ecosystem dominated by tamarisk along a section of the lower Colorado River in southern California. The results were compared against the estimates of a previously validated remotely sensed energy balance model for the year 2008 at two different spatial scales. A pixel-wide comparison showed good correlation (R2 = 0.86), with a mean residual error of less than 104 mm·year-1 (18%). This error reduced to less than 95 mm·year-1 (15%) when larger areas were used in comparisons. In addition, the accuracy improved significantly when areas with no and low vegetation cover were excluded from the analysis. The SSS method was then applied to estimate the riparian water use for a 23-year period (1988–2010). The average annual water use over this period was 748 mm·year-1 for the entire study area, with large spatial variability depending on vegetation density. Comparisons with two independent water use estimates showed significant differences. The MODIS evapotranspiration product (MOD16) was 82% smaller, and the crop-coefficient approach employed by the US Bureau of Reclamation was 96% larger, than that from the SSS method on average

Drought and its impact on agricultural water resources in Oklahoma

The Oklahoma Cooperative Extension Service periodically issues revisions to its publications. The most current edition is made available. For access to an earlier edition, if available for this title, please contact the Oklahoma State University Library Archives by email at [email protected] or by phone at 405-744-631

Tracking drought using soil moisture information

The Oklahoma Cooperative Extension Service periodically issues revisions to its publications. The most current edition is made available. For access to an earlier edition, if available for this title, please contact the Oklahoma State University Library Archives by email at [email protected] or by phone at 405-744-631

Development and evaluation of an agricultural drought index by harnessing soil moisture and weather data

A new agricultural drought index was developed for monitoring drought impacts on agriculture in Oklahoma. This new index, called the Soil Moisture Evapotranspiration Index (SMEI), estimates the departure of aggregated root zone moisture from reference evapotranspiration. The SMEI was estimated at five locations across Oklahoma representing different climates. The results showed good agreement with existing soil moisture-based (SM) and meteorological drought indices. In addition, the SMEI had improved performance compared to other indices in capturing the effects of temporal and spatial variations in drought. The relationship with crop production is a key characteristic of any agricultural drought index. The correlations between winter wheat production and studied drought indices estimated during the growing period were investigated. The correlation coefficients were largest for SMEI (r > 0.9) during the critical crop growth stages when compared to other drought indices, and r decreased by moving from semi-arid to more humid regions across Oklahoma. Overall, the results suggest that the SMEI can be used effectively for monitoring the effects of drought on agriculture in Oklahoma.Peer reviewedBiosystems and Agricultural Engineerin

Estimating Impacts of Subsurface Drainage on Evapotranspiration Using Remote Sensing

Subsurface (tile) drainage is a common management practice on naturally poorly drained agricultural soils to provide for more timely field operations and improved productivity. Installation of artificial subsurface drainage systems may alter the soil water budget by changing timing and rate of subsurface water flow, potentially linking with altered hydrology response from the field to watershed scale. Therefore, the main objective of this study was to examine the impact of subsurface tile drainage on evapotranspiration (ET) at the field scale, which is the largest component of soil water budget after precipitation. The study was conducted for four growing seasons at three different sites from southeast North Dakota (Site 1, near Fairmount), southwest Minnesota (Site 2, near Tracy), and southeast South Dakota (Site 3, near Lennox). The growing seasons of 2009 and 2010 was planted to corn and soybean for Site 1, 2008 with soybean at Site 2, and 2013 with corn at Site 3. The METRIC (Mapping Evapotranspiration at high Resolution with Internalized Calibration) procedure was applied to estimate high resolution (30 m) ET from the field with and without subsurface tile drainage systems. Comparison of estimated ET is based on areas of interest (AOI) created within the satellite image delineating subfields with and without tile drainage. Each AOI for representing different drainage conditions had equal numbers of pixels. Areas represented by AOI for Site 1,Site 2, and Site 3 were 11.9 ha (132 pixels), 6.3 ha (70 pixels), and 7.6 ha (84 pixels), respectively.Greater ET rates were obtained from fields without tile drainage than those from tile drained fields during the early growing season. During the later growing season, ET rates were greater from tile drained fields. The total growing season ET was greater from fields without tile drainage for all study years except 2009 (corn) of study Site 1. The total ET was greater from the undrained field by 6% (33mm), 25% (107 mm), less than 0.5% (1 mm) for study period of 2010 (soybean) at Site 1, 2008 (soybean) at Site 2, and 2013 (corn) at Site 3, respectively. Greater ET from the tile drained field occurred for only 2009 (corn) at Site 1, which was less than 1% (3 mm). For the mid-June to mid- August period, the total ET was greater by 3% (8mm) from the drained field for 2009 at Site 1, 2% (7 mm) higher from the undrained field for 2010 at Site 1, 24% (59 mm) higher from the undrained field for 2008 at Site 2, and 2% higher from the undrained field for 2013 at Site 3

Evaluation of streamflow predictions from LSTM models in water- and energy-limited regions in the United States

The application of Long Short-Term Memory (LSTM) models for streamflow predictions has been an area of rapid development, supported by advancements in computing technology, increasing availability of spatiotemporal data, and availability of historical data that allows for training data-driven LSTM models. Several studies have focused on improving the performance of LSTM models; however, few studies have assessed the applicability of these LSTM models across different hydroclimate regions. This study investigated the single-basin trained local (one model for each basin), multi-basin trained regional (one model for one region), and grand (one model for several regions) models for predicting daily streamflow in water-limited Great Basin (18 basins) and energy-limited New England (27 basins) regions in the United States using the CAMELS (Catchment Attributes and Meteorology for Large-sample Studies) data set. The results show a general pattern of higher accuracy in daily streamflow predictions from the regional model when compared to local or grand models for most basins in the New England region. For the Great Basin region, local models provided smaller errors for most basins and substantially lower for those basins with relatively larger errors from the regional and grand models. The evaluation of one-layer and three-layer LSTM network architectures trained with 1-day lag information indicates that the addition of model complexity by increasing the number of layers may not necessarily increase the model skill for improving streamflow predictions. Findings from our study highlight the strengths and limitations of LSTM models across contrasting hydroclimate regions in the United States, which could be useful for local and regional scale decisions using standalone or potential integration of data-driven LSTM models with physics-based hydrological models

A Modeling Framework for Deriving Daily Time Series of Evapotranspiration Maps Using a Surface Energy Balance Model

Surface energy balance models have been one of the most widely used approaches to estimate spatially distributed evapotranspiration (ET) at varying landscape scales. However, more research is required to develop and test an operational framework that can address all challenges related to processing and gap filling of non-continuous satellite data to generate time series of ET at regional scale. In this study, an automated modeling framework was developed to construct daily time series of ET maps using MODIS imagery and the Surface Energy Balance System model. The ET estimates generated from this modeling framework were validated against observations of three eddy-covariance towers in Oklahoma, United States during a two-year period at each site. The modeling framework overestimated ET but captured its spatial and temporal variability. The overall performance was good with mean bias errors less than 30 W m−2 and root mean square errors less than 50 W m−2. The model was then applied for a 14-year period (2001–2014) to study ET variations across Oklahoma. The statewide annual ET varied from 841 to 1100 mm yr−1, with an average of 994 mm yr−1. The results were also analyzed to estimate the ratio of estimated ET to reference ET, which is an indicator of water scarcity. The potential applications and challenges of the ET modeling framework are discussed and the future direction for the improvement and development of similar automated approaches are highlighted

Estimating Impacts of Agricultural Subsurface Drainage on Evapotranspiration Using the Landsat Imagery-Based METRIC Model

Agricultural subsurface drainage changes the field hydrology and potentially the amount of water available to the crop by altering the flow path and the rate and timing of water removal. Evapotranspiration (ET) is normally among the largest components of the field water budget, and the changes in ET from the introduction of subsurface drainage are likely to have a greater influence on the overall water yield (surface runoff plus subsurface drainage) from subsurface drained (TD) fields compared to fields without subsurface drainage (UD). To test this hypothesis, we examined the impact of subsurface drainage on ET at two sites located in the Upper Midwest (North Dakota-Site 1 and South Dakota-Site 2) using the Landsat imagery-based METRIC (Mapping Evapotranspiration at high Resolution with Internalized Calibration) model. Site 1 was planted with corn (Zea mays L.) and soybean (Glycine max L.) during the 2009 and 2010 growing seasons, respectively. Site 2 was planted with corn for the 2013 growing season. During the corn growing seasons (2009 and 2013), differences between the total ET from TD and UD fields were less than 5 mm. For the soybean year (2010), ET from the UD field was 10% (53 mm) greater than that from the TD field. During the peak ET period from June to September for all study years, ET differences from TD and UD fields were within 15 mm (<3%). Overall, differences between daily ET from TD and UD fields were not statistically significant (p > 0.05) and showed no consistent relationship

Dry Season Evapotranspiration Dynamics over Human-Impacted Landscapes in the Southern Amazon Using the Landsat-Based METRIC Model

Although seasonal and temporal variations in evapotranspiration (ET) in Amazonia have been studied based upon flux-tower data and coarse resolution satellite-based models, ET dynamics over human-impacted landscapes are highly uncertain in this region. In this study, we estimate ET rates from critical land cover types over highly fragmented landscapes in the southern Amazon and characterize the ET dynamics during the dry season using the METRIC (Mapping Evapotranspiration at high Resolution with Internalized Calibration) model. METRIC, a Landsat-based ET model, that generates spatially continuous ET estimates at a 30 m spatial resolution widely used for agricultural applications, was adapted to the southern Amazon by using the NDVI indexed reference ET fraction (ETrF) approach. Compared to flux tower-based ET rates, this approach showed an improved performance on the forest ET estimation over the standard METRIC approach, with R2 = 0.73 from R2 = 0.70 and RMSE reduced from 0.77 mm/day to 0.35 mm/day. We used this approach integrated into the METRIC procedure to estimate ET rates from primary, regenerated, and degraded forests and pasture in Acre, Rondônia, and Mato Grosso, all located in the southern Amazon, during the dry season in 2009. The lowest ET rates occurred in Mato Grosso, the driest region. Acre and Rondônia, both located in the southwestern Amazon, had similar ET rates for all land cover types. Dry season ET rates between primary forest and regenerated forest were similar (p > 0.05) in all sites, ranging between 2.5 and 3.4 mm/day for both forest cover types in the three sites. ET rates from degraded forest in Mato Grosso were significantly lower (p < 0.05) compared to the other forest cover types, with a value of 2.03 mm/day on average. Pasture showed the lowest ET rates during the dry season at all study sites, with the dry season average ET varying from 1.7 mm/day in Mato Grosso to 2.8 mm/day in Acre