Fog and haze are disaster weathers which endanger human health and affect social and economic development. Accurate and detailed monitoring data can play an important role in the prevention and control of fog and haze. The accuracy of China Meteorological Administration Land Data Assimilation System (CLDAS) visibility and relative humidity fusion products in identifying fog, light fog and haze is analyzed by using the observation data of national stations in Tianjin and its surrounding areas from December 1, 2017 to November 30, 2020, Himawari-8 L1 full-disk data and L3 aerosol optical depth product. The results show that compared with the station observation data, the average detection rates of CLDAS products in identifying light fog, fog and haze are 90.4%, 84.2% and 78.8%, respectively. The detection rates of light fog in different months are 81.1%-96.4%. In the months with more fog and haze, the detection rates are about 80.0%. The cases analysis shows that the fog, light fog and haze identified by CLDAS products are basically consistent with the results of Himawari-8 satellite and observations. The failure of CLDAS products to correctly identify fog, light fog and haze mainly shows that fog is misjudged as light fog (3.8%-21.4% at different stations) and haze is missed (8.6%-25.0% at different stations). When the horizontal visibility of the station is between 0 and 0.75 km, the error of CLDAS visibility mainly causes fog to be mistakenly identified as light fog. When the horizontal visibility of the station is between 0.75 and 7.5 km，the error of CLDAS visibility mainly leads to haze being missed. When the station visibility is between 7.5 and 15 km, the error of CLDAS visibility mainly leads to light fog and haze being reported empty. When the relative humidity of the station is greater than 40% and less than or equal to 60%, the error of CLDAS relative humidity mainly leads to haze being misjudged as light fog. In general, the accuracy of CLDAS products in identifying fog, light fog and haze in Tianjin area is good, which can provide reference for fine monitoring of fog, light fog and haze, and improve the status quo of scarce visibility observation stations and insufficient space coverage in fog and haze monitoring.

Based on observation data of temperature and precipitation in Tianjin region during 1921-2016, the precipitation from the Global Precipitation Climatology Centre (GPCC-P) and the temperature from the Climate Research Unit (CRU-T) were evaluated and it was found that they performed well. On the basis of these results, the standardized precipitation evapotranspiration index (SPEI) was further used to analyze the temporal-spatial evolution characteristics of drought for almost a century in Tianjin region and its change trend in the future was estimated. The results are as follows: (1) Drought mainly occurred in the early 1940s, late 1990s and early 2000s, and it was dominated by mild drought and moderate drought in four seasons, and its high frequency season evolved from autumn, winter to spring and summer. (2) During six periods, climate tendency of SPEI showed “increasing and decreasing” in other seasons, but it showed “increasing, decreasing and increasing” in autumn, moreover the decreasing tendency in summer was most significant with a climate tendency of -0.3 per decade at Ninghe station during 1961-2010. (3) During 1921-1970, 1931-1980, 1941-1990, it was found that precipitation was dominating factor for the wet tendency in spring and winter, while temperature and precipitation were factors in summer and autumn; during 1951-2000, 1961-2010, 1971-2016, drought tendency in spring was affected mainly by temperature, in summer and winter it was synergistically affected by temperature and precipitation. (4) There was a negative correlation between SPEI and PDO in four seasons during 1921-2016 in Tianjin region, the correlation in spring and summer decreased from northwest to southeast, while that decreased from southeast to northwest in autumn and winter. (5) In the future, it will present drought trendency in summer in the whole region and in winter in the southwestern region, while drought trendency in spring and wet trendency in autumn will not significant.