**2.3. MOD16 data**

The MOD16 algorithm [12, 13] was developed in the context of the Earth Observing System/ NASA (EOS/NASA) program, aiming to estimate global evapotranspiration using data from Moderate Resolution Imaging Spectroradiometer (MODIS) sensor (Terra and Aqua) and meteorological data from Global Modeling and Assimilation Office (GMAO). In general terms, MOD16 is a revision of the algorithm proposed by [20], who adapted the Penman‐Monteith equation (Eq. (1)) to be used with remote sensing data:

$$
\lambda E = \frac{sA + \rho C\_p \left(e\_{\rm sat} - e\right) / r\_a}{s + \chi \left(1 + r\_s / r\_a\right)} \tag{1}
$$

where *λE* is the latent heat flux (W m−2) and *λ* represents the latent heat of evaporation (J kg−1), *s* = *d*(*e*sat)/*dT* is the slope of the curve which relates saturated pressure of water (*e*sat) and temperature (Pa K−1), *A* is the energy available at surface (W m−2), *ρ* represents air density (kg m −3), *Cp* is the specific heat of air (J kg−1 K−1), *e* is the real pressure of water vapor (Pa), *rs* is the surface resistance, *ra* is the aerodynamic resistance (s m−1), and *γ* represents the psychrometric constant (66 Pa K−1).

MODIS input data required for MOD16 algorithm have spatial resolution between 500 m and 1 km, and include global products of land use and land cover (MOD12Q1), leaf area index (LAI) and photosynthetically active radiation (PAR‐MOD15A2), and albedo (MCD43B2). Regarding the meteorological parameters required for the algorithm, daily reanalysis data of GMAO referring to incident solar radiation, air temperature, and water vapor pressure, with spatial resolution of 1.00° × 1.25°, are used [13, 21]. In summary, MOD16 data have a spatial resolution of 1 km and covers ~109 million km2 of vegetated global areas. Among the products generated, we highlight the potential and actual evapotranspiration and potential and actual latent heat flux products, in intervals of eight (MOD16A2) and 30 days (MOD16A3) [22].

MOD16 data were acquired from the Numerical Terradynamic Simulation Group/The University of Montana repository (http://www.ntsg.umt.edu/project/mod16). Tiles H13V10 and H13V11, corresponding to the monthly real evapotranspiration product, in mm month−1, were selected for the period between January 2000 and December 2010. As MOD16 data are available in sinusoidal projection, images were initially reprojected to geographic coordinates with datum WGS 84 and converted to GeoTIFF format using the MODIS Reprojection Tool (MRT). Then, a number of steps were undertaken using ENVI 4.5. These steps included clipping of the study area, multiplication by scale factors, and application of the land‐water and urban areas mask over the datasets.
