The aim of this paper is to describe the drought events in the Zhanghe upstream comprehensively. Firstly, monthly precipitation data were selected to calculate standardized precipitation index. And then, both drought duration and drought severity were identified according to runoff theory. Finally, Copula function was adopted to establish joint distribution between drought duration and drought severity to explore the spatial and temporal distribution of drought characteristics. The results show that the highest frequent drought events in the Zhanghe upstream from 2001 to 2020 is 3 months drought, and the drought severity ranges from 2.24 to 4.92; There is a strong positive correlation between drought duration and drought severity, and Frank Copula function is the most optimal joint distribution function of them; The joint return period of drought characteristics ranges from 18.56-23.94 years, and the northwest and southeast parts of the Zhanghe upstream basin are the two key drought risk areas; The co-occurrence return period of drought characteristics ranges from 22.25-31.94 years, and the northwest, northeast and southeast parts of the Zhanghe upstream basin are the three key drought risk areas. Consequently, it can be obtained that the joint distribution can analyze drought events comprehensively, and thus provide scientific guidance for thorough evaluation of drought.
| 科 Family | 属数 Number of genus | 种数 Number of species | 占总种数比例 Percentage of total species (%) | 属 Genus | 种数 Number of species | 占总种数比例 Percentage of total species (%) |
|---|---|---|---|---|---|---|
| 鹅膏菌科Amanitaceae | 2 | 11 | 5.26 | 鹅膏菌属 Amanita | 10 | 4.78 |
| 小菇科 Mycenaceae | 2 | 12 | 5.74 | 丝盖伞属 Inocybe | 5 | 2.39 |
| 多孔菌科 Polyporaceae | 8 | 14 | 6.70 | 蜡蘑属 Laccaria | 5 | 2.39 |
| 红菇科 Russulaceae | 3 | 23 | 11.00 | 小皮伞属 Marasmius | 6 | 2.87 |
| 小菇属 Mycena | 11 | 5.26 | ||||
| 光柄菇属 Pluteus | 5 | 2.39 | ||||
| 红菇属 Russula | 17 | 8.13 | ||||
| 栓菌属 Trametes | 5 | 2.39 |