Dry-wet evolution characteristics and response to ENSO events in the Minjiang River basin from 1962 to 2021
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Abstract:
The global average temperature has risen by 1.09 ℃ over the past century. The increase in temperature leads to an increase in evapotranspiration and atmospheric water vapor content, which causes the rate of the water cycle to accelerate, changing the global pattern of the spatial and temporal distribution of water and heat, thus causing the frequent occurrence of droughts, floods, and other extreme events. The Minjiang River basin is an important water conservation area in the southeast of China, with an average annual precipitation between 1 400 mm and 2 000 mm. But the inter-annual unevenness, inter-seasonal variability, and impulsive intra-seasonal distribution of precipitation, as well as the complexity of geographic distribution, make the basin regional, seasonal dry and wet problems occur frequently. Therefore, it is of great significance to study the characteristics of regional dry and wet evolution for economic and social development and ecological environment construction.Based on the daily precipitation data of 29 meteorological stations in the Minjiang River basin from 1962 to 2021, the standardized precipitation index (SPI), combined with the Mann-Kendall test and Morlet wavelet analysis, were used to analyze the characteristics of spatial and temporal changes of dryness and wetness of the Minjiang River basin under different time scales, and combined with the sea surface temperature anomaly index (SSTA), to investigate the effects of ENSO events on the evolution of dryness and wetness in the Minjiang River.The results showed that the Minjiang River basin showed a non-significant wetting trend at different spatial and temporal scales, with a weak wetting trend in spring, and the basin showed a wet-dry-wet-dry distribution from east to west. The summer SPI changed abruptly after the 1990s, showing a significant wetting trend, with a significant wetting trend in the southeastern part of the basin. In autumn, the drought trend began to intensify after 1995, with a tendency toward aridification in the southern part of the basin. Winter is more prone to extreme wet and dry events than other seasons. Extreme wet and dry events at all levels throughout the basin tended to increase on an annual scale. On the seasonal scale, the four types of wet events were on an increasing trend in summer, while extreme drought, severe drought, and mild drought events were all on an increasing trend in fall and mainly occurred after the 1990s. The SPI of the Minjiang River basin has a short-cycle change pattern of 3-8 a and 11-16 a and a long-cycle change pattern of 20-30 a. During the occurrence of ENSO cold and warm events, the mean value of SPI is ?0.124 and 0.193 respectively, and the correlation coefficients between SPI and the intensity of ENSO cold and warm events are ?0.158 and 0.242 respectively, which indicate that there is a greater possibility of wetness when warm events occur, and a greater possibility of drought when cold events occur. The occurrence of ENSO warm events has a significant effect on the wet and dry of the Minjiang River basin during the same period up to the 4-month lag months of dryness and wetness, and the occurrence of ENSO cold events has a significant effect on the dryness and wetness in the lag of 3-5 months.The Minjiang River basin as a whole shows an insignificant wetting trend, with significant wetting in the summer after the 1990s, a tendency to drought in the fall after 1995, and a greater tendency to extreme wet and dry events in the winter than in other seasons. Spatially, a more significant wetting trend exists in the southeastern portion of the basin. There is an increasing trend of wetting and drying events at all levels throughout the basin, with wetting events occurring more often in the summer and drying events occurring more often in the fall and winter. There is a cycle shift of dry-wet-dry alternation in the Minjiang River basin in the 20-30 a scale range. The dry-wet and ENSO warm and cold events in the Minjiang River basin are most significant at a lag of 1-4 months and 3-5 months, respectively.
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