On the relationships between satellite-based drought index and gross primary production in the North Korean croplands, 2000-2012

Drought is one of the main constraints on vegetation growth and crop yields, although land ecosystems differ in their sensitivity to drought. Satellite-based vegetation indices, such as the Normalized Difference Vegetation Index (NDVI), have been used in many drought studies, but they may not sufficiently represent the water content of vegetated land. Alternatively, the Normalized Difference Drought Index (NDDI) has been developed by integrating the NDVI and Normalized Difference Water Index (NDWI). In this letter, we examine how drought affects crop growth by quantifying the relationships between NDDI and the Gross Primary Production (GPP) derived from the moderate-resolution imaging spectroradiometer. In the North Korean croplands, NDDI had a strong negative correlation with GPP during 2000-2012. The relationships were more significant under relatively dry conditions (e.g., dry seasons or dry regions). The impacts of NDDI on GPP was greater in summer than in spring, which indirectly shows summer drought may be more critical to crop productivity. The NDDI-GPP relationship was slightly time-lagged in spring, which indicates that vegetation productivity may not always respond instantly to surface dryness. The NDDI can be a viable option for measuring the impacts of drought on vegetation and agriculture over a wide area.