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The North China Plain (NCP) is the most important agricultural production area in China. Crop production in the NCP is sensitive to changes in both climate and management practices. While previous studies showed a negative impact of climatic change on crop yield since 1980s, the confounding effects of climatic and agronomic factors have not been separately investigated. This paper used 25 years of crop data from three locations (Nanyang, Zhengzhou and Luancheng) across the NCP, together with daily weather data and crop modeling, to analyse the contribution of changes in climatic and agronomic factors to changes in grain yields of wheat and maize. The results showed that the changes in climate were not uniform across the NCP and during different crop growth stages. Warming mainly occurred during the vegetative (preflowering) growth stage of wheat and maize, while there was a cooling trend or no significant change in temperatures during the postflowering stage of wheat (spring) or maize (autumn). If varietal effects were excluded, warming during vegetative stages would lead to a reduction in the length of the growing period for both crops, generally leading to a negative impact on crop production. However, autonomous adoption of new crop varieties in the NCP was able to compensate the negative impact of climatic change. For both wheat and maize, the varietal changes helped stabilize the length of preflowering period against the shortening effect of warming and, together with the slightly reduced temperature in the postflowering period, extend the length of the grain-filling period. The combined effect led to increased wheat yield at Zhengzhou and Luancheng; increased maize yield at Nanyang and Luancheng; stabilized wheat yield at Nanyang, and a slight reduction in maize yield at Zhengzhou, compared with the yield change caused entirely by climatic change. [ABSTRACT FROM AUTHOR]

Growing demand on groundwater resources and the semi-arid climate in the North China Plain (NCP) highlight the need for improved understanding of connections between regional climate change and groundwater recharge. Hydrologic time series of precipitation and groundwater levels were analyzed in three representative geographical zones throughout the NCP for the period of 1960-2008 using trend analysis and spectral analysis methods. A significant change point around 1975 is followed by a long-term decline trend in precipitation time series, which coincides with the Pacific Decadal Oscillation positive phase. However, the magnitudes of groundwater level variability due to heavy pumping overwhelm the low-frequency signal of groundwater levels. Nonlinear trends that related to long-term climatic variability and anthropogenic activities are removed by using the Singular Spectrum Analysis method. Spectral analyses of the detrended residuals demonstrate significant short-term oscillations at the frequencies of 2-7 years, which have strong correlations with the El Niño-Southern Oscillation modes. This study contributes to improved understanding of dynamic relationship between groundwater and climate variability modes in the NCP and demonstrates the importance of reliable detrending methods for groundwater levels that are affected greatly by pumping. Copyright © 2015 John Wiley & Sons, Ltd. [ABSTRACT FROM AUTHOR]