Geology topics

Prasanna H. Gowda

Publications and source records attributed to Prasanna H. Gowda.

3 recordsLinked to original sources

USGS2015

Accuracy assessment of NOAA gridded daily reference evapotranspiration for the Texas High Plains

The National Oceanic and Atmospheric Administration (NOAA) provides daily reference evapotranspiration (ET ref ) maps for the contiguous United States using climatic data from North American Land Data Assimilation System (NLDAS). This data provides large-scale spatial representation of ET ref , which is essential for regional scale water resources management. Data used in the development of NOAA daily ET ref maps are derived from observations over surfaces that are different from short (grass — ET os ) or tall (alfalfa — ET rs ) reference crops, often in nonagricultural settings, which carries an unknown discrepancy between assumed and actual conditions. In this study, NOAA daily ET os and ET rs maps were evaluated for accuracy, using observed data from the Texas High Plains Evapotranspiration (TXHPET) network. Daily ET os , ET rs and the climatic data (air temperature, wind speed, and solar radiation) used for calculating ET ref were extracted from the NOAA maps for TXHPET locations and compared against ground measurements on reference grass surfaces. NOAA ET ref maps generally overestimated the TXHPET observations (1.4 and 2.2 mm/day ET os and ET rs , respectively), which may be attributed to errors in the NLDAS modeled air temperature and wind speed, to which reference ET ref is most sensitive. Therefore, a bias correction to NLDAS modeled air temperature and wind speed data, or adjustment to the resulting NOAA ET ref , may be needed to improve the accuracy of NOAA ET ref maps.

Texas↗

USGS2013

Operational evapotranspiration mapping using remote sensing and weather datasets: A new parameterization for the SSEB approach

The increasing availability of multi-scale remotely sensed data and global weather datasets is allowing the estimation of evapotranspiration (ET) at multiple scales. We present a simple but robust method that uses remotely sensed thermal data and model-assimilated weather fields to produce ET for the contiguous United States (CONUS) at monthly and seasonal time scales. The method is based on the Simplified Surface Energy Balance (SSEB) model, which is now parameterized for operational applications, renamed as SSEBop. The innovative aspect of the SSEBop is that it uses predefined boundary conditions that are unique to each pixel for the "hot" and "cold" reference conditions. The SSEBop model was used for computing ET for 12 years (2000-2011) using the MODIS and Global Data Assimilation System (GDAS) data streams. SSEBop ET results compared reasonably well with monthly eddy covariance ET data explaining 64% of the observed variability across diverse ecosystems in the CONUS during 2005. Twelve annual ET anomalies (2000-2011) depicted the spatial extent and severity of the commonly known drought years in the CONUS. More research is required to improve the representation of the predefined boundary conditions in complex terrain at small spatial scales. SSEBop model was found to be a promising approach to conduct water use studies in the CONUS, with a similar opportunity in other parts of the world. The approach can also be applied with other thermal sensors such as Landsat.

Journal of the American Water Resources Associatio↗

USGS2008

Simplified Surface Energy Balance (SSEB) approach for estimating actual ET: An evaluation with lysimeter data

Evapotranspiration (ET) is an essential component of the water balance and a major consumptive use of irrigation water and precipitation on cropland. Numerous energy balance (EB) algorithms have been developed to make use of remote sensing data to estimate ET regionally. However, a review of different ET mapping algorithms shows that most EB models are complex to use and may not be suitable for operational ET remote sensing. Efforts are being made to simplify procedures to estimate regional ET mainly through the scaling of reference ET. The Simplified Surface Energy Balance (SSEB) is one such method. In this study, the SSEB approach was applied to six Landsat TM images covering a major portion of the Southern High Plains (parts of the Texas Panhandle and northeastern New Mexico) that were acquired during the 2007 cropping season. Performance of the SSEB was evaluated by comparing estimated ET with measured daily ET from four large monolithic lysimeters, with each lysimeter located in the center of a 210 by 225 m field at the USDA_ARS Conservation and Production Research Laboratory, Bushland, Tex. [350 11' N, 1020 06' W; 1,170 m elevation MSL]. Results indicated that the SSEB can provide ET estimates with reasonable accuracy for the Bushland location. However, more evaluation is needed for different agroclimatological conditions in the region.

Conference Paper↗