Land improvement, or bright spots, is identified by combination of: 1) a positive trend in sum NDVI for those areas where
NDVI does not depend on rainfall; 2) for areas where NDVI is correlated with rainfall, a positive trend in rain-use efficiency;
and 3) a positive trend in energy-use efficiency, i.e., climate-adjusted NDVI.
Energy-use efficiency(EUE) is represented by the ratio of annual sum NDVI to annual accumulated temperature (day degrees
above 0oC), calculated from CRU 2.1 monthly data. CRU TS 2.1 comprises monthly values of station-observed meteorological
data from the beginning of the 20th century, gridded at 0.5 degree resolution (Mitchell and Jones 2005). Monthly temperature
values since January 1981 are used to calculate energy-use efficiency.