Figure 4(a) is the spatial distribution of PCI variations at 18 meteorological stations in the UHRB. The PCI values of most stations (except for WN and YX) in the basin exhibit positive trends, but only 3 stations passed the significance test.
Annual precipitation in the UHRB displays both spatial and temporal variations.
As a result, the temporal distribution of precipitation can produce noticeably different effects on natural and social processes across the UHRB, and such variations are of particular interest for water management, flood planning, soil erosion prevention, water availability assessment in natural ecosystems, and so on.
Among the geographical features of the UHRB, longitude is the most important variable that affects the spatial distribution of precipitation.
The UHRB is characterized by an area vulnerable to climate change and exhibits obvious differences in the spatial distribution of precipitation.
(1) The model Y = X exp [-b [(100 - X).sup.c]] can adequately represent the statistical structure of precipitation rates better than the model Y = aX exp(bX) in the UHRB. The basin PCI exhibits a gradient from west to east, with higher values in the west and smaller values in the east.
The results suggest that the daily precipitation distribution did not significantly change in the UHRB during the 1959-2015 period.
Overall, the investigation of the PCI, PCD, and PCP reveals the characteristics of daily precipitation in the UHRB. These research findings are of considerable importance for local water resources management, and they provide a scientific basis for the development of policy for the mitigation of natural disasters such as floods and droughts.