Abstract: Based on soil moisture (VSM), land surface temperature (LST) data of FY-3C/MWRI (microwave imager) and precipitation data of TRMM3B43 in the growing season (April-October) during 2015-2017, three indices of Precipitation Condition Index (PCI), Temperature Condition Index (TCI) and Soil Moisture Condition Index (SMCI) were obtained through downscaling and normalization. The three indices were merged to establish a Microwave Integrated Drought Index (MIDI), which was used to assess drought status in the arid regions of northwest China. The results showed that: (1) Temporally, drought occurred in the arid regions of Northwest China every year from 2015 to 2017, with the dominance of extreme drought and heavy drought. Spatially, drought events had obvious regional differentiation. The degree of drought increased from east to west, and the trend of change was slightly aggravated and then alleviated. (2) From the perspective of spatiotemporal evolution, 10.57% of area in the arid northwest China became wetter during 2015-2017, and 12.87% of the area became drier. Drought within a single year was continuously reduced from April to August, and continued to increase from August to October. (3) The MIDI index had a better detection effect than the single drought index on short-term drought in the study area. The correlation of MIDI index with Humidity Index was optimal, with a high actual agreement rate in space. Our results provide a basis for drought monitoring and related research using other microwave remote sensing data.

Key words: subtropical region, relative humidity of air, plant number., negative air ion, phytotron, air temperature