Processing MOD16A2 Product (PET/ET) in the Ganges-Brahmaputra-Meghna River Basin for Hydrological Modeling in GH2MF2 Non-Profit Project
In the Non-Profit GH2MF2 association we have processed the MODIS product (Moderate Resolution Imaging Spectroradiometer) MOD16A2: MODIS / Terra Net Evapotranspiration 8-Day L4 Global 500 m SIN Grid V006 in the basin of the Ganges-Brahmaputra-Meghna rivers. The objective is to help the calibration and validation of the hydrological models in the project, initially in the Koshi river basin that will be extended to the other basins of the Ganges-Brahmaputra-Meghna System.
However, and following the founding principles of the association Non-Profit GH2MF2, we make available to the scientific community and government entities related to hydrology, water resources, agriculture of the states of Nepal, China, Bhutan, India, Bangladesh and Myanmar the processed and unified dataset in ESRI ASCII Grid format. Due to the size of the Dataset we make available for download the period between 01/01/2017 until 06/17/2018 in the following link. If you are interested in the complete Dataset please contact the secretariat of the Association GH2MF2 firstname.lastname@example.org
Global climate change will affect precipitation and ET, and hence influence the renewable freshwater resources ET is the second largest component (after precipitation) of the terrestrial water cycle at the global scale, since ET returns more than 60% of precipitation on land back to the atmosphere (Korzoun et al., 1978, L’vovich and White, 1990 ) and thus conveys an important constraint on water availability at the land surface. In addition, ET is an important energy flux since land ET uses up more than half of the total solar energy absorbed by land surfaces (Trenberth et al., 2009). Accurate estimation of ET not only meets the growing competition for the limited water supplies and the need to reduce the cost of the irrigation projects, but also it is essential to projecting potential changes in the global hydrological cycle under different climate change scenarios (Teuling et al 2009).
MODIS instrument is operating on both the Terra and Aqua spacecraft. It has a viewing width of 2,330 km and views the entire surface of the Earth every one to two days. Its detectors measure 36 spectral bands and it acquires data at three spatial resolutions: 250-m, 500-m, and 1,000-m.
We have created a Dataset from the MOD16A2 data of potential evapotranspiration (PET) and real evapotraspiration (ET) at a daily time scale with spatial resolution of 0.0083º (about 1 Km at the equator) with geoDatum WGS84, 446 rows and 3133 columns with center of the first cell in the upper left corner: Longitude = 73.0041º, Latitude 32.9977º. For this, we have processed 9 tiles (download Excel sheet with the files) in the Sinusoidal grid tiling system used in many Land MODIS products from January 01, 2001 to June 17, 2018, the tiles are:
MODIS filenames (i.e., the local granule ID) follow a naming convention which gives useful information regarding the specific product. For example, the filename MOD09A1.A2006001.h08v05.006.2015113045801.hdf indicates:
MOD09A1 – Product Short Name
.A2006001 – Julian Date of Acquisition (A-YYYYDDD)
.h08v05 – Tile Identifier (horizontalXXverticalYY)
.006 – Collection Version
.2015113045801 – Julian Date of Production (YYYYDDDHHMMSS)
.hdf – Data Format (HDF-EOS)
The MOD16A2 Version 6 Evapotranspiration / Latent Heat Flux product is an 8-day composite product produced at 500 meter pixel resolution. The algorithm used for the MOD16 data product is based on the logic of the Penman-Monteith equation, which includes inputs of daily meteorological reanalysis data along with MODIS remotely sensed data such as vegetation property dynamics, albedo, and land cover.
Provided in the MOD16A2 product are layers for composited Evapotranspiration (ET), Latent Heat Flux (LE), Potential ET (PET) and Potential LE (PLE) along with a quality control layer. Two low resolution browse images are also available for each MOD16A2 granule, (1) ET and (2) LE. The pixel values for the two Evapotranspiration layers (ET and PET) are the sum of the eight days within the composite period and the pixel values for the two Latent Heat layers (LE and PLE) are the average of the eight days within the composite period . Note that the last 8-day period of each year is a 5 or 6-day composite period, depending on the year.
Flowchart of the improved MOD16 ET algorithm. LAI: leaf area index; FPAR: Fraction of Photosynthetically Active Radiation.
Running, S., Mu, Q., Zhao, M. (2017). MOD16A2 MODIS / Terra Net Evapotranspiration 8-Day L4 Global 500m SIN Grid V006 [Data set]. NASA EOSDIS Land Processes DAAC. doi: 10.5067 / MODIS / MOD16A2.006
Special thanks to Salvatore Falanga Bolognesi, PhD collaborator of the “GH2MF2 – Association for a Participated Global Hydrological Monitoring and Flood Forecasting System” for processing and post-processing this dataset.