A global analysis of the impact of drought on net primary productivity

We investigated the impact of drought on interannual variability of NPP from 1997 to 2009 using the standardized precipitation evapotranspiration index (SPEI) drought index and satellite-derived vegetation greenness converted net primary productivity (NPP). We found that SPEI and NPP were coupled and in phase on a global scale. We then used the K ppen climate classification to study the SPEI-NPP relations regionally and found that while NPP and SPEI were positively related in arid and in seasonal dry regions, the opposite occurs in most boreal regions. However, high intensity drought events, such as the 2003 drought in Europe, will lead to a reduction of NPP despite NPP being usually limited by temperature and radiation here. Our findings suggest that the strong positive relation between global average moisture availability and NPP is a composite of the positive relation across dry regions and the coherent NPP decline during and after intensive drought event in humid regions. The spatial patterns of drought impact on NPP could thus be categorized by climate classification, which implies that the predication of climate zone evaluation will contribute to the quantification of the future terrestrial carbon cycle.