青藏高原东侧“雅安天漏”旱涝年降水特征

利用四川省雅安市1951~2008年逐日降水资料和1969~2000年逐小时降水资料,统计分析了青藏高原东侧雅安地区4个典型旱年和4个典型涝年的降水量、降水频率的多时间尺度变化特征。结果表明,雅安旱年的平均年降水量为1242.9mm,涝年的平均年降水量比旱年多1010mm。旱年汛期降水量占旱年降水总量的70.4%,涝年汛期降水量超出旱年一倍,且占涝年降水总量的81.1%。旱、涝年降水量的季节变化明显,且涝年的季节差异更加显著;雨强与降水量的季节变化相似,夏季达到最大,且旱、涝年年雨强和汛期雨强的差异很明显;旱、涝年之间的雨日差异要小的多,季节差异也不突出。旱、涝年降水量和雨日的最大值、最小值出现月份不同,旱年降水量7月最多、1月最少,而涝年降水量8月最多、12月最少。另外,旱、涝年白天、夜间的月降水量和月雨日最大值出现时间不同,并且不同降水强度,旱、涝年降水量和雨日的逐月变化也有较大差异;旱、涝年降水日变化与夜雨特征都突出,但夜间降水量和频次远远大于白天。旱、涝年降水量和频次的最大值、最小值出现时间有差异,旱年最大小时降水量在01时,最小在14时。涝年夜间小时降水量为双峰结构,最大小时降水量在23时,另一最大值在03时,最小在16时。旱年和涝年最大小时降水频次均出现在00时,最小分别出现在14时和15时。并且,降水量和频次从谷值到峰值的增加速率超过了从峰值到谷值的衰减速率;进一步分析发现,随着降水强度的增加,其夜间降水量越容易出现多峰值的波动,且旱、涝年夜间降水量和频次的差值也越明显。其中,旱年中雨和大雨降水量和频次高于涝年,但涝年暴雨降水量和频次远高于旱年。 

Precipitation Characteristics of Yaan in Drought and Flood Years

Multiple-time-scale variations of precipitation amount and precipitation frequency in Yaan region in four typical drought years and four typical flood years are investigated by using the daily precipitation data from 1951 to 2008 and the hourly precipitation data from 1969 to 2000.The result showed that the average annual precipitation in drought years was 1242.9mm Precipitation of flood season in drought years accounted for 70.4% of the total precipitation in drought years.The precipitation of flood season in flood years is twice of it in drought years,and it accounted for 81.1% of the total.Seasonal characteristic of precipitation distribution in drought and flood is obvious,especially in flood years.Rainfall intensity is similar to the seasonal changes in precipitation,reaches its maximum in summer,and the difference between annual rainfall intensity and rainfall intensity of flood season was obvious both in drought and flood years.The difference of wet days between drought and flood was much smaller,either was the seasonal differences.The maximum and minimum value of precipitation occurred in different months.In drought years,precipitation reached the maximum value in July,and the minimum value appeared in January.While,in flood years,the maximum value appeared in August,and the minimum value appeared in December.In addition,the maximum value the precipitation and wet days in the day and night appeared in different time,so was the rainfall intensity.The monthly change of precipitation and wet days was also quite different in drought and flood years.Characteristics of diurnal variations of precipitation and mid-night rainfall were prominent.Both the amount and frequency of mid-night rainfall is much larger than that of in the day.But the appearance time of peak and valley value were different in drought years and in flood years.In drought years,the peak of precipitation usually appeared at 1 a.m.,and there was a valley at 2 p.m..In drought years,mid-night precipitation showed a bimodal structure,maximum value appeared at 11 p.m.and at 3 a.m.,and the valley was at 4 p.m..The maximum frequency in drought years and in flood years both occurred at 0 a.m.and the minimum occurred at 2p.m.and 3 p.m.respectively.The increase rate from valley to peak is much faster than the decrease rate from peak to valley.Further analysis revealed that with the rainfall intensity increasing,the mid-night precipitation was more prone to form multi peaks,and the difference of amount and frequency of mid-night rainfall between drought years and flood years was more obvious.The amount and frequency of moderate and heavy rain in drought years are more than that of in flood years,but the amount and frequency of rainstorm in drought years is far less than that of in flood years.