Trends in agricultural heat and solar radiation resources in Northeast China: A multistage spatio‐temporal analysis

Climate change has changed the distribution of climate resources in crop growing season, and caused some impacts on agricultural production. Based on daily meteorological data collected at 71 meteorological stations in Northeast China, trends at multi-temporal scales (decadal, annual, monthly, and 10-day) and spatial patterns of heat resources [temperature, frost-free period (FFP)] and solar radiation resources [growing season's sunshine hour (GSS)] are estimated over the period 1961-2012. The period of 2000-2012 has been successively warmer than the previous decades with higher mean values for both temperature and FFP, and temperature had an abrupt increasing change in the 1980s. An increasing trend was identified for the daily mean temperature in the study area, with the trend value (0.30 degrees C decade(-1)) double the global warming rate (0.14 degrees C decade(-1)). As the last frost date advanced by 1.9 days decade(-1) in spring and the first frost date delayed by 1.6 days decade(-1) in fall, FFP increased by 17.9 days in recent 52 years with the average trend value of 3.5 days decade(-1). Temperature in February exhibited the highest increasing rate; furthermore, the maximum temperature trends occurred in the last 10 days of February at most stations. Daily sunshine hours decreased in June, July, and August, but GSS showed small changes at decadal and annual scales because of the prolonged FFP. In summary, climate change has prolonged FFP, increased the heat resource, and slightly changed solar radiation resource during crop growing season, which is beneficial for agriculture in Northeast China.