It is unclear whether slash and burn
and related land cover changes affect water storage on a scale
visible in GRACE. Anyway, since the maps are not deseasoned, what we
see here is predominantly the seasonal cycle in total water storage
which has a wide span between wet and dry season, which was already shown to be large in some papers (e.g. Wahr et al. 2004; Crowley et al. 2008). Thus the change in the gravity field can likely be explained by the seasonal cycle.
The figures show drought indicators
derived from total water storage deficits. For analysing trends
one would need to look at trend maps which are available in the
literature. For attributing observed trends or changes to individual drivers like snow melt, permafrost change or land surface change (fires) one would need to conform the observed data with model simulations. There are plenty of studies in the literature.
The map shows loss of total water storage (surface, groundwater, etc) over 15 years which is a short timespan. Using model simulations, several published studies have attributed these changes to unsustainable use of groundwater over India, and this has been confirmed from groundwater well observations, so there is a high confidence. For other regions of the world, trends have been observed with GRACE but it is often difficult to attribute them so causes – this could be changes in agricultural practice like irrigation but also be natural climate variability.
Cheers,