According to Nature Communications July 2020:
Globally, of the 44.5 million km^2 of drylands, 6% of these areas experienced desertification (i.e., significant negative change in NDVImax), 41% showed significant greening (i.e., significant positive change), and 53% had no significant change between 1982 and 2015 (Fig. 1a). The mean (±1 SD) of the area-weighted dryland vegetation change, as represented by the change in NDVImax was 0.031 ± 0.053. We estimated the scale of desertification to be 2.70 million km^2, which is significantly below a previous estimate of ~10.5 million km^2 over the same region, but over a different time window (1982 and 2003)^1. A large part of this discrepancy can be attributed to climatic differences in the end dates of the studies (2003 vs. 2015), with increased rainfall over regions including the Sahel and India.
(NDVI means "Normalized Difference Vegetation Index")
So overall there was more area with an increase in vegetation, not a decrease.
Counting areas with decreased vegetation only, and disregarding the much greater area with increased vegetation, 270 million hectares had less vegetation 33 years later, about 8.2 million hectares per year.
Note: A commentator below seems astounded by the well know fact that there is currently negative net desertification and wants to see additional references:
According to Desertification published by the International Panel on Climate Change (IPCC):
the drylands are greening on average
Fig 3.6 from the IPCC publication shows increased vegetation areas in shades of green and decreased vegetation areas in red, 1982-2015. They grey areas are areas to which the UN definition of desertification ("land degradation in arid, semi-arid and sub-humid areas") does not apply.
See also Impact of CO2 fertilization on maximum foliage cover across the globe's warm, arid environments Geophysical Research Letters (Volume 40, June 2013, pages 3031-3035):
The increase in water use efficiency of photosynthesis with rising [atmospheric CO2 level] has long been anticipated to lead to increased foliage cover in warm, arid environments ... and both satellite and ground observations from the world's rangelands reveal widespread changes toward more densely vegetated and woodier landscapes ... Our results suggest that [atmospheric CO2 level] has played an important role in this greening trend and that, where water is the dominant limit to growth, cover has increased in direct proportion to the CO2-driven rise in [water use efficiency of photosynthesis].