How does dewfall affect drought assessment in different climate regions in China

Dewfall is an important source of additional precipitation, but it is frequently ignored in water balance calcu-lations. In this study, the dewfall of 523 weather stations in China was calculated. An improved drought index SPI-cor was proposed by substituting the precipitation with the summation of dewfall and precipitation by the SPI calculation method, where dewfall was calculated by the Penman-Monteith equation with the GLDAS-2 data. The temporal and spatial distributions characteristics of dewfall were discussed, and the spatial applicability of SPI and SPI-cor was determined. The results indicated that the dewfall formation is periodic, with more than 60% of the dewfall occurring between April and August. The amount of dewfall is lower than that of precipitation. The dewfall in China has a distribution pattern of high dewfall in the northeast and northwest but low dewfall in the center and south. The proportion of dewfall in precipitation increases from south to north with the exception of northwestern China. Comparing of SPI to SPI-cor, the influence of dewfall in arid, semi-arid, sub-humid and humid areas declines in turn in accordance with the proportion of dewfall in precipitation of the four regions and is opposite to the correlation coefficients of SPI and SPI-cor. Dewfall has an average impact of one drought grade on the assessment of drought as long as it works. With the performance of SPI and SPI-cor at different weather stations, historical drought events, and vegetation response to drought, SPI is better in northeastern China and eastern Inner Mongolia, while SPI-cor is more applicable in central and northwestern China; the difference between SPI and SPI-cor drought grades are not noticeable in southern China. Therefore, adopting SPI and SPI-cor to evaluate drought in different regions can help to make more accurate drought assessment.