Temporal-spatial analysis of cloud structure in Khuzestan province using ERA5 database reanalysis data

Cloudiness is one of the most important climate elements that plays a major role in the rainfall and water balance of any region. In addition, the radiation budget of each region is largely controlled by the cloudiness and cloud characteristics of each region. Knowledge of the temporal and spatial structure of clouds in each region plays an essential role in planning and checking programs based on water and energy resources. The main goal of this research is to analyze the temporal-spatial structure of cloudiness in Khuzestan province using gridded data of ECMWF cloud database version ERA5 in Khuzestan province during the statistical period of 1990-2020. The cloud data for Khuzestan province in NC format was obtained monthly from the Copernicus integrated climate database, which included the height of the base or cloud floor, the percentage of sky cloud cover by the upper, middle and lower clouds of each pixel was 0.25 degrees of arc. . By calling the mentioned data in the ARC-GIS environment and spatial averaging by separating the cold and warm periods of the year, 30-year average maps of the warm and cold periods of the year were produced for the two factors of total cloudiness and cloud base height. On the other hand, the sky cloud percentage values were also calculated through spatial averaging in Khuzestan province for each year (1990-2020). The results showed that, firstly, in both hot and cold periods of the year, the northeastern and mountainous parts of the province had higher cloud cover than the plains and lowlands of the province. In the cold period of the year, the percentage of cloudiness of the sky varied between 25 and 60%, while in the warm period of the year, the percentage of sky cloudiness reached less than 5%. In addition, it was observed that in the province of Khuzestan, the highest share of cloudiness in the cold period of the year is related to the upper clouds (cirrus family including cirrus, cirrustratus and cirrocumulus with a height of more than 4 thousand meters). These clouds have a share of 25% in the cloud coverage of Khuzestan province during the cold period of the year. Meanwhile, middle clouds (alto family clouds including altocumulus and altostratus) have a 16% share in the cloud cover of the sky of Khuzestan province. In terms of the cloudiness time series trend during the period of 1990-2020, despite significant annual changes in the amount of cloudiness of the province's sky, no significant trend was observed in the changes of cloudiness in Khuzestan province during the last three decades.