Abstract
Understanding the temporal inequality in precipitation is of great importance for water resource management, environmental risk management, and ecological conservation. This study investigated the spatial patterns and trends of the daily precipitation concentration over the Yarlung Tsangpo River Basin using the concentration index (CI) and the Lorentz asymmetric coefficient (LAC). A Mann–Kendall test and Hurst’s rescaled range analysis were used to detect the change in CI trends. The CI ranged from 0.58 to 0.65, suggesting that a quarter of the rainiest days contributed approximately 69–78% of the total precipitation. The LAC analysis indicated that the nonuniform distribution of precipitation was mainly attributed to a large proportion of days with light rainfall. Compared with that of the central region, the daily precipitation in the western and eastern regions was more irregular. At a seasonal scale, the dry season had a less homogeneous spatial distribution of CI compared to that of the wet season. Most areas exhibited no significant trends in CI from 1970 to 2017. A quarter of the stations presented a significant downward trend in CI, which were primarily found in the central and northern regions. In addition, the future trends of CI in most areas mostly agree with those of the current state; however, the majority of stations exhibited an uneven precipitation distribution in the dry season.
Highlights
Precipitation is a fundamental process of the water cycle [1, 2] and shows high temporal and spatial variability [3, 4]
Spatial Pattern of the Daily Precipitation Concentration. e annual concentration index (CI) and Lorentz asymmetric coefficient (LAC) were calculated for 16 meteorological stations in the Yarlung Tsangpo River Basin (YTRB) for the period 1970–2017. e values of the regression coefficients and the CI and LAC are presented in Table 2. e annual CI value ranged between 0.58 and 0.65, suggesting that the lowest values observed are related to regions where 25% of the rainiest days accounted for 69% of the total precipitation, while the highest values are associated with places where 25% of the rainiest days contribute to 78% of the total precipitation (Table 2)
According to the proposed classifications for the CI [11], the averaged value of the CI (0.60) over the YTRB is within high concentration categories, which implied that 25% of the rainiest days could concentrate more than 70% of the total precipitation. e annual LAC value ranged between 0.86 and 0.95, with a median value of 0.89, which illustrates a high precipitation concentration attributed to a large number of light rainfall events
Summary
Precipitation is a fundamental process of the water cycle [1, 2] and shows high temporal and spatial variability [3, 4]. E precipitation concentration refers to the temporal heterogeneity of precipitation, which is applicable in research of water-related environmental risks [13, 14]. High precipitation concentrations, meaning a small number of rainy days with a large amount of total precipitation, could trigger floods and droughts [15, 16]. To quantify precipitation heterogeneity on a monthly scale, Oliver [17] developed the precipitation concentration index (PCI) using the monthly precipitation data within a given year. To evaluate daily precipitation irregularity in a given year, Martin Vide [19] proposed the concentration index (CI) to determine the percentage of precipitation contributed by the days falling in each rainfall class. To evaluate daily precipitation irregularity in a given year, Martin Vide [19] proposed the concentration index (CI) to determine the percentage of precipitation contributed by the days falling in each rainfall class. e CI has been widely applied to study rainfall on both global [12]
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