Background The change of dry-wet conditions has great influence on industrial development, agricultural production and layout, as well as ecological environment, etc. The Huaihe River Basin is an overlapping area of climate, high and low latitude, sea and land facies in the north and south of China, and the study of its dry-wet pattern has also become a hot topic in recent years. Therefore, we carried out this study in order to provide case support for scientifically understanding the response difference law of the dry-wet pattern of Huaihe River Basin and regional system under the background of global change, to make a new attempt to explore the evolution process and quantitative means of surface dry-wet process, and also to provide background environmental data for soil and water conservation under the transition climate belt.

Methods The Huaihe River Basin was taken as the research area, and the monthly meteorological data from 27 stations in the basin from 1959 to 2018 were selected. Based on FAO-PM56 and climate trend slope analysis, this paper introduced cloud model to carry out a quantitative description of the dry-wet pattern of the study area, the missing data were interpolated by the average data of neighboring months, and the seasonal division was carried out according to the meteorological standard and the principle of facilitating the study of the inter-annual variation.

Results 1) The average dry-wet index in the study area was 0.882, showing a rising trend of "5 peaks and 5 valleys", with a rising rate of 0.000 4/a. The cloud characteristics of the dry-wet index indicated that the overall dispersion of dry-wet index K was low, and the randomness and fuzziness were small in the past 60 years. 2) The inter-annual variation of dry-wet index K in different seasons presented the characteristics of summer > autumn > spring >winter, showing the pattern of decline in spring and autumn, of rise in summer and winter. The distribution entropy value of the four seasons had high unevenness and instability. The amplitude of change was the most stable in spring, followed by summer and winter, and the biggest decline was in autumn. 3) On the spatial scale, the distribution of dry-wet patterns in the Huaihe River Basin was similar to that of precipitation. The variation rate increased from north to south, and other stations except the northeast tended to become wetter, the dry-wet index K was more discrete and uneven in spatial distribution compared with the time distribution of the dry-wet index.

Conculsions The dry-wet pattern of Huaihe River Basin is characterized by large spatio-temporal difference, and the quantitative description of dry-wet index K based on cloud model can be used as an important assisted means to describe the dry-wet pattern. However, due to the complexity and diversity of potential evapotranspiration factors, the mechanism of its influence on the overall dry-wet condition remains to be further studied.