Aims Vegetation has strong temporal response to climate variables in some regions. The normalized differential vegetation index (NDVI) is generally recognized as a good indicator of terrestrial vegetation, so it can be used to analyze temporal responses of vegetation to climate variables. This study addresses two key questions: a) How quickly and over what time period does NDVI respond to different patterns of climate variables? b) How does NDVI respond to weather variation for different temperate steppe types of northern China?

Methods We calculated 1) linear correlations between monthly climate variables and NDVI for 1983-1997, 2) NDVI-precipitation correlation coefficients, with precipitation in four different time periods (1-4 months) and four different time lags (0-3 month lags) to evaluate the time period over which precipitation most strongly influences on NDVI and 3) NDVI-temperature correlation coefficients for the current and previous month.

Important findings The correlation coefficients between NDVI and concurrent climate variables were all significant in three temperate steppe types. There is a strong relationship between precipitation and NDVI in temperate steppe of northern China. Correlation coefficients between NDVI and precipitation are high for specific combinations of time duration and lag. In terms of time lag, NDVI was most strongly related to the previous month, although differences existed among different steppe types. In terms of time duration, NDVI was most strongly related to the sum of precipitation over three months than one, two or four month periods. Precipitation from February back to November of the previous year was positively correlated with NDVI early in the growing season in meadow steppe, and there was a strong correlation between NDVI and precipitation for the preceding 1-2 months in the mid and late growing season in desert steppe and typical steppe. Temperature was moderately correlated with NDVI during the growing season, but differences existed among steppe types. For typical steppe and meadow steppe, temperature was positively correlated with NDVI early in the growing season. For desert steppe, NDVI was moderately related with temperature early in the growing season and negatively correlated with temperature in the mid growing season.