The observed relationships between wheat and climate in China

Recent changes in climate have had a measurable impact on crop yield in China. The objective of this study is to investigate how climate variability affects wheat yield in China at different spatial scales. First the response of wheat yield to the climate at the provincial level from 1978 to 1995 for China was analysed. Wheat yield variability was only correlated with climate variability in some regions of China. At the provincial level, the variability of precipitation had a negative impact on wheat yield in parts of southeast China, but the seasonal mean temperature had a negative impact on wheat yield in only a few provinces, where significant variability in precipitation explained about 23-60% of yield variability, and temperature variability accounted for 37-41% of yield variability from 1978 to 1995. The correlation between wheat yield and climate for the whole of China from 1985 to 2000 was investigated at five spatial scales using climate data. The Climate Research Unit (CRU) and National Centers for Environmental Prediction (NCEP) proportions of the grid cells with a significant yield-precipitation correlation declined progressively from 14.6% at 0.5 degrees to 0% at 5 degrees scale. In contrast, the proportion of grid cells significant for the yield-temperature correlation increased progressively from 1.9% at 0.5 degrees scale to 16% at 5 degrees scale. This indicates that the variability of precipitation has a higher association with wheat yield at small scales (0.5 degrees, 2 degrees/2.5 degrees) than at larger scales (4 degrees/5.0 degrees): but wheat yield has a good association with temperature at all levels of aggregation. The precipitation variable at the smaller scales (0.5 degrees, 2 degrees/2.5 degrees) is a dominant factor in determining inter-annual wheat yield variability more so than at the larger scales (4 degrees/5 degrees). We conclude that in the current climate the relationship between wheat yield and each of precipitation and temperature becomes weaker and stronger, respectively, with an increase in spatial scale. (C) 2010 Elsevier B.V. All rights reserved.