Wang, RN; Liu, YB (2020). Recent declines in global water vapor from MODIS products: Artifact or real trend?. REMOTE SENSING OF ENVIRONMENT, 247, 111896.

Atmospheric water vapor plays a key role in the global water and energy cycles. Accurate estimation of water vapor and consistent representation of its spatial-temporal variation are critical to climate analysis and model validation. This study used ground observational data from global radiosonde and sunphotometer networks to evaluate MODIS (MODerate-resolution Imaging Spectroradiometer) precipitable water vapor (PWV) products for 2000-2017. The products included the thermal-infrared (TIR) (Collection 6, C006) and its updated version (Collection 061, C061), and near-infrared (NIR) products (C061). Our results demonstrated that compared to its earlier version subject to sensor crosstalk problem, the C061_TIR data showed improved accuracy in terms of bias, standard deviation, mean absolute error, root mean square error, and coefficient of determination, regression slope and intercept. Among the PWV products, C061_NIR data achieved the best overall performance in accuracy evaluation. The C061_NIR revealed the PWV had a multi-year average of 2.50 +/- 0.08 cm for the globe, 2.03 +/- 0.06 cm for continents, and 2.70 +/- 0.09 cm for oceans in 2000-2017. The PWV values yielded an increasing rate of 0.015 cm/year for the globe, 0.010 cm/year for continents, and 0.017 cm/year for oceans. Nearly 98.95% of the globe showed an increasing trend, 80.74% of statistical significance, mainly distributed within and around the tropical zones. The findings should be valuable for understanding of global water and energy cycles.