Observed daily temperature and precipitation from 121 meteorological stations and satellite-based 8-day average gross primary productivity (GPP) from MOD17A2 are utilized to develop the linear correlation models between 8-day accumulated average temperature, maximum temperature, minimum temperature, precipitation and accumulated GPP in the monsoon zone in Northern China during 2000–2013. Based on the derived thresholds and coefficients of these models, variability in the starting date of GPP accumulation, length of GPP accumulating period, ending date of GPP accumulation as well as GPP accumulation rate on forest, grassland and cropland ecosystems are investigated under two Representative Concentration Pathways (RCP4.5 and RCP8.5) of the Regional Spectral Model (RSM). Finally, the substantial impacts of climate changes including maximum, average, minimum temperature and precipitation on ecosystem productivity are evaluated. Results suggest that average and minimum temperature can predict GPP more accurately than maximum temperature and precipitation. Besides, the starting and ending dates of GPP accumulation are sensitive to the variability in four climatic factors whereas the GPP accumulation period and rate are more sensitive to the variability in average and maximum temperature. Additionally, future climate changes tend to prolong the GPP accumulation period and increase the GPP accumulation rate, thus increasing GPP.
Utilizing land cover change (LCC) information together with MODIS land surface temperature in Jing-Jin-Ji area in 2000, 2005 and 2010, spatiotemporal difference of urban heat island (UHI) effects and the factors influenced UHI is explored. Results reveal that the seasonal fluctuations of daytime UHI is bigger than that of nighttime UHI. More than 92.8% of the urban have UHI in the nighttime every season. The strongest daytime UHI happens in summer, but more than 85% of the cities have urban cooling effect in winter. The nighttime UHI in different seasons appear to be similar. The water in urban has different influence to UHI in daytime and nighttime which is to weaken the UHI and to enhance the UHI. The grass in urban enhance the UHI in the daytime of spring and summer and in the nighttime of all seasons but weaken the UHI in the daytime of winter. The forest and the crop land in the urban have the same effect which are weaken the UHI in the daytime of spring, summer and autumn and in the nighttime of all seasons but enhance the UHI in the daytime of winter.
Based on the observed temperature, precipitation, wind speed, soil moisture and other basic meteorological data in the north part of Northern China Plain from China Meteorological Administration, three major variables of water cycle: precipitation, soil moisture and water requirement on cropland are calculated. Besides, the water cycle model of cropland in the study area is built together with designed water shortage index to analyze the temporal and spatial variability in water shortage of cropland in the study area by ten-day intervals. Results suggest that the water shortage of cropland in the study area is serious through all growth period. The study area witnesses droughts in most months with sufficient moisture only in the mid July. Spring is the most serious period of droughts on cropland, and the droughts are more severe in central and southern of Hebei Province than that in other areas. Furthermore, the stress of water shortage on cropland in autumn is much relieved compared with that in spring. However, droughts in the northwest part of study area are extremely serious in autumn. Meanwhile, droughts in Hengshui area and western Beijing are the most serious through the whole crop growth stage. Relevant conclusions can provide references to regional water management and irrigation of cropland.
