Since late 1970s, climate warming has been widely recognized. In the Midwest, farmers cannot rely on the normal calendar anymore, and it has become critically necessary to evaluate the most recent climate trends relative to growing season in order to conduct adaptation efforts for agriculture. Based on the homogenized historical monthly temperature and precipitation records during the period of 1980–2013 from 302 observing stations in the 12 Midwestern US states, we investigate the climate trends on four timescales: monthly, early growing season, late growing season, and the entire growing season. The climate metrics include maximum temperature, minimum temperature, average temperature, diurnal temperature range, and precipitation. Nonparametric Sen's Slope together with the nonparametric Mann–Kendall test is used to estimate the decadal trend and to detect the statistical significance. The results show that growing season average temperature has increased at a rate of 0.15 °C decade−1 over the Midwest United States. Within the growing season, minimum temperature is increasing faster in the early growing season, especially in June, while maximum temperature is increasing faster in the late growing season, especially in September. Spatially, statistically significant (p ≤ 0.05) growing season warming is more focused in the southern part of the region in the early growing season but in the northern part of the region in the late growing season. Over the Midwest, dominant trends in diurnal temperature range are decreasing during most months, with the exception of September. The majority of the locations show increasing trends in growing season precipitation, yet few are statistically significant. Furthermore, precipitation has been increasing in the early growing season but decreasing in the late growing season. This within‐season reversing trend in precipitation is found in 8 of 12 Corn Belt states: Illinois, Iowa, Michigan, Minnesota, Missouri, Nebraska, North Dakota, and Wisconsin.

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a b s t r a c tRice is one of the main crops grown in southern China. Global climate change has significantly altered the local water availability and temperature regime for rice production. In this study, we explored the influence of climate change on suitable rice cropping areas, rice cropping systems and crop water requirements (CWRs) during the growing season for historical (from 1951 to 2010) and future (from 2011 to 2100) time periods. The results indicated that the land areas suitable for rice cropping systems shifted northward and westward from 1951 to 2100 but with different amplitudes. The land areas suitable for single ricecropping systems (SRCS) and early double rice-cropping systems (EDRCS) decreased, whereas the land areas suitable for middle double rice-cropping systems (MDRCS) and late double rice-cropping systems (LDRCS) expanded significantly. Among the rice-cropping systems, the planting area suitable for SRCS was the largest during the historical period , whereas the suitable planting area for LDRCS was the largest during the future period (2070-2100). Spatially, the water requirement of rice during the growing season exhibited a decreasing trend from southeast to northwest from 1951 to 2010. Temporally, the regional water requirement of rice during the growing season decreased from 720 mm to 700 mm (1981-2010) as a result of solar radiation and evapotranspiration. However, the water requirement was predicted to increase from 1027 mm to 1150 mm (2071-2100). During the past six decades, the planting area suitable for double rice-cropping systems increased by 2.7 × 10 4 km 2 and, consequently, the CWR and irrigation water requirement (IWR) increased by 1.1 × 10 10 and 8.8 × 10 9 m 3 , respectively. In addition, under A1B scenarios, the CWR and IWR of double rice-cropping systems are expected to increase by 1.6 × 10 11 and 1.2 × 10 11 m 3 , respectively, from 2071-2100 compared with the historical period of 1951-1980. The regional CWR and IWR were predicted to increase respectively by 8% and 6% from 2011 to 2040, by 17% and 19% from 2041 to 2070, and by 20% and 24% from 2071 to 2100 compared with 1951-1980. These increases can be attributed to climate warming, which expands the suitable planting area for multiple-cropping systems and extends the growing season for late-maturing rice varieties. Our study aims to provide a scientific guide for planning future cropping systems and optimizing water management in the southern rice cropping region of China.

No abstract

A signifi cant trend of decreasing solar radiation has been observed in Northeast China over the past six decades. Such a decline in solar radiation could negatively impact maize (Zea mays L.) production. Th e improved cultivated hybrids may have adapted to these changes in solar radiation. In this study, four commonly cultivated maize hybrids in Northeast China were selected for a 2-yr fi eld study. Two hybrids were released in the 1970s and the other two were released in the 1990s. In comparison with the maize hybrids released in the 1970s, the maize hybrids released in the 1990s exhibited signifi cant increases in both dry matter at maturity (P < 0.05) and grain yields (P < 0.05), although the harvest index (HI) showed no signifi cant diff erence. Th e greater dry matter accumulation was primarily responsible for the yield increase observed in the 1990s' hybrids. Th e greater dry matter accumulation occurred primarily during the tasseling-to-maturity stage. Our results indicated signifi cant improvements (P < 0.05) in crop growth rate and radiation use effi ciency (RUE) in 1990s' hybrids, particularly during the tasseling-to-maturity stage. Additionally, the net photosynthetic rate (NPR) of the ear-leaf before 1200 h was also signifi cantly improved in the 1990s' hybrids. Th e fraction of photosynthetically active radiation (PAR) interception on the third leaf above the ear-leaf was increased during the tasseling-to-maturity stage and signifi cantly correlated with maize grain yields (P < 0.01), indicating that the increase in the fraction of PAR interception at this layer contributed to the higher grain yield in the 1990s hybrids.